const API_URL = '/api';
let allDrugs = []; // level-1 summaries: no packs, no batches
let loadedDrugDetails = new Map(); // drugId → full drug with variant packs (level-2)
let loadedVariantBatches = new Map(); // variantId → Batch[] (level-3)
let currentDrug = null;
let showLowStockOnly = false;
let selectedLocationFilter = '';
let searchTerm = '';
let expandedDrugs = new Set();
let expandedVariants = new Set();
let currentUser = null;
let accessToken = null;
let deliveryDrugId = null;
let deliveryLineCounter = 0;
let deliveryLocations = [];
let currentDispenseBatches = [];
let currentDispenseLegacyQuantity = 0;
let _gtinMappingPendingRefresh = false;
let _gtinMappingPendingVariantId = null;
let _gtinMappingPendingRestore = null;  // { drugId, variantId, packId } — auto-select after reload
let _gtinMappingWaitingForNewDrug = null; // Set of drug IDs before add-drug; resolved on first loadDrugs
let _highlightedBatchLot = null;   // lot number to highlight after a main-screen scan
let _highlightedVariantId = null;  // variant the highlighted batch belongs to
let _highlightClearTimer = null;   // timer to auto-remove the highlight

/** Build a human-readable pack label from pack fields, e.g. "Box of 28" */
function packLabel(packOrUnitName, packSize) {
    // Accept either (pack object) or (unit_name string, size number)
    let unitName, size;
    if (typeof packOrUnitName === 'object' && packOrUnitName !== null) {
        unitName = packOrUnitName.pack_unit_name;
        size = packOrUnitName.pack_size_in_base_units;
    } else {
        unitName = packOrUnitName;
        size = packSize;
    }
    const displaySize = size === Math.floor(size) ? Math.floor(size) : size;
    const unit = String(unitName || 'pack');
    return `${unit.charAt(0).toUpperCase()}${unit.slice(1)} of ${displaySize}`;
}

function resetDisposeBatchModal() {
    const form = document.getElementById('disposeBatchForm');
    if (form) {
        form.reset();
    }
    const batchIdInput = document.getElementById('disposeBatchId');
    const batchNameInput = document.getElementById('disposeBatchName');
    if (batchIdInput) batchIdInput.value = '';
    if (batchNameInput) batchNameInput.value = '';
}

function closeDisposeBatchModal() {
    resetDisposeBatchModal();
    const modal = document.getElementById('disposeBatchModal');
    if (modal) {
        closeModal(modal);
    }
}

// Toast notification system
function showToast(message, type = 'info', duration = 3000) {
    const container = document.getElementById('toastContainer');
    if (!container) return;
    
    const toast = document.createElement('div');
    toast.className = `toast ${type}`;
    
    const icons = {
        success: '✓',
        error: '✕',
        warning: '⚠',
        info: 'ℹ'
    };
    
    toast.innerHTML = `
        <span class="toast-icon">${icons[type] || icons.info}</span>
        <span class="toast-message">${message}</span>
    `;
    
    container.appendChild(toast);
    
    // Auto remove after duration
    setTimeout(() => {
        toast.classList.add('fade-out');
        setTimeout(() => {
            container.removeChild(toast);
        }, 300);
    }, duration);
}

// Initialize on page load
document.addEventListener('DOMContentLoaded', () => {
    checkAuth();
});

// Check if user is already logged in
function checkAuth() {
    const token = localStorage.getItem('accessToken');
    const user = localStorage.getItem('currentUser');
    
    if (token && user) {
        accessToken = token;
        currentUser = JSON.parse(user);
        showMainApp();
    } else {
        showLoginPage();
    }
}

// Show login page
function showLoginPage() {
    document.getElementById('loginPage').style.display = 'flex';
    document.getElementById('mainApp').style.display = 'none';
    
    const loginForm = document.getElementById('loginForm');
    if (loginForm) loginForm.addEventListener('submit', handleLogin);
}

// Show main app
function showMainApp() {
    document.getElementById('loginPage').style.display = 'none';
    document.getElementById('mainApp').style.display = 'block';
    
    // Handle backward compatibility: convert old is_admin format to role
    if (!currentUser.role && currentUser.is_admin !== undefined) {
        currentUser.role = currentUser.is_admin ? 'admin' : 'user';
    }
    // Default to 'user' if role is still undefined
    if (!currentUser.role) {
        currentUser.role = 'user';
    }
    
    const userDisplay = document.getElementById('currentUser');
    if (userDisplay) {
        const roleLabel = currentUser.role.charAt(0).toUpperCase() + currentUser.role.slice(1);
        userDisplay.textContent = `👤 ${currentUser.username} [${roleLabel}]`;
    }
    
    const adminBtn = document.getElementById('adminBtn');
    if (adminBtn) {
        adminBtn.style.display = currentUser.role === 'admin' ? 'block' : 'none';
    }
    
    const locationsBtn = document.getElementById('locationsBtn');
    if (locationsBtn) {
        locationsBtn.style.display = currentUser.role === 'admin' ? 'block' : 'none';
    }

    const reportsBtn = document.getElementById('reportsBtn');
    if (reportsBtn) {
        reportsBtn.style.display = currentUser.role === 'admin' ? 'block' : 'none';
    }
    
    // Hide action buttons for read-only users
    const isReadOnly = currentUser.role === 'readonly';
    const addDrugBtn = document.getElementById('addDrugBtn');
    const dispenseBtn = document.getElementById('dispenseBtn');
    const printNotesBtn = document.getElementById('printNotesBtn');
    const receiveDeliveryBtn = document.getElementById('receiveDeliveryBtn');
    
    if (addDrugBtn) addDrugBtn.style.display = isReadOnly ? 'none' : 'block';
    if (dispenseBtn) dispenseBtn.style.display = isReadOnly ? 'none' : 'block';
    if (printNotesBtn) printNotesBtn.style.display = isReadOnly ? 'none' : 'block';
    if (receiveDeliveryBtn) receiveDeliveryBtn.style.display = isReadOnly ? 'none' : 'block';
    
    setupEventListeners();
    loadDrugs();
}

// Handle login
async function handleLogin(e) {
    e.preventDefault();
    const username = document.getElementById('loginUsername').value;
    const password = document.getElementById('loginPassword').value;
    
    try {
        const response = await fetch(`${API_URL}/auth/login`, {
            method: 'POST',
            headers: { 'Content-Type': 'application/json' },
            body: JSON.stringify({ username, password })
        });
        
        if (!response.ok) {
            throw new Error('Invalid credentials');
        }
        
        const data = await response.json();
        accessToken = data.access_token;
        currentUser = data.user;
        
        localStorage.setItem('accessToken', accessToken);
        localStorage.setItem('currentUser', JSON.stringify(currentUser));
        
        document.getElementById('loginForm').reset();
        const errorDiv = document.getElementById('loginError');
        if (errorDiv) errorDiv.style.display = 'none';
        showMainApp();
    } catch (error) {
        const errorDiv = document.getElementById('loginError');
        if (errorDiv) {
            errorDiv.textContent = error.message;
            errorDiv.style.display = 'block';
        }
    }
}

// Handle register
// Logout
function handleLogout() {
    localStorage.removeItem('accessToken');
    localStorage.removeItem('currentUser');
    accessToken = null;
    currentUser = null;
    const loginForm = document.getElementById('loginForm');
    if (loginForm) loginForm.reset();
    const registerForm = document.getElementById('registerForm');
    if (registerForm) {
        registerForm.style.display = 'none';
    }
    const form = document.getElementById('loginForm');
    if (form) form.style.display = 'block';
    showLoginPage();
}

// API helper with authentication
async function apiCall(endpoint, options = {}) {
    const headers = {
        'Content-Type': 'application/json',
        ...options.headers
    };
    
    if (accessToken) {
        headers['Authorization'] = `Bearer ${accessToken}`;
    }
    
    const response = await fetch(`${API_URL}${endpoint}`, {
        ...options,
        headers
    });
    
    if (response.status === 401) {
        handleLogout();
        throw new Error('Authentication expired');
    }
    
    return response;
}

// Setup event listeners
function setupEventListeners() {
    const drugForm = document.getElementById('drugForm');
    const variantForm = document.getElementById('variantForm');
    const editVariantForm = document.getElementById('editVariantForm');
    const dispenseForm = document.getElementById('dispenseForm');
    const editForm = document.getElementById('editForm');
    const printNotesForm = document.getElementById('printNotesForm');
    const disposeBatchForm = document.getElementById('disposeBatchForm');
    const addModal = document.getElementById('addModal');
    const addVariantModal = document.getElementById('addVariantModal');
    const editVariantModal = document.getElementById('editVariantModal');
    const dispenseModal = document.getElementById('dispenseModal');
    const editModal = document.getElementById('editModal');
    const printNotesModal = document.getElementById('printNotesModal');
    const disposeBatchModal = document.getElementById('disposeBatchModal');
    const batchReceiveModal = document.getElementById('batchReceiveModal');
    const receiveDeliveryModal = document.getElementById('receiveDeliveryModal');
    const addDrugBtn = document.getElementById('addDrugBtn');
    const dispenseBtn = document.getElementById('dispenseBtn');
    const printNotesBtn = document.getElementById('printNotesBtn');
    const cancelAddBtn = document.getElementById('cancelAddBtn');
    const cancelVariantBtn = document.getElementById('cancelVariantBtn');
    const cancelEditVariantBtn = document.getElementById('cancelEditVariantBtn');
    const cancelDispenseBtn = document.getElementById('cancelDispenseBtn');
    const cancelEditBtn = document.getElementById('cancelEditBtn');
    const cancelDisposeBatchBtn = document.getElementById('cancelDisposeBatchBtn');
    const cancelBatchReceiveBtn = document.getElementById('cancelBatchReceiveBtn');
    const cancelReceiveDeliveryBtn = document.getElementById('cancelReceiveDeliveryBtn');
    const addDeliveryLineBtn = document.getElementById('addDeliveryLineBtn');
    const addVariantFromDeliveryBtn = document.getElementById('addVariantFromDeliveryBtn');
    const addPackSizeFromDeliveryBtn = document.getElementById('addPackSizeFromDeliveryBtn');
    const addVariantPackRowBtn = document.getElementById('addVariantPackRowBtn');
    const addEditVariantPackRowBtn = document.getElementById('addEditVariantPackRowBtn');
    const variantUnitSelect = document.getElementById('variantUnit');
    const variantStrengthInput = document.getElementById('variantStrength');
    const editVariantUnitSelect = document.getElementById('editVariantUnit');
    const dispenseModeInputs = document.querySelectorAll('input[name="dispenseMode"]');
    const dispenseSourceInputs = document.querySelectorAll('input[name="dispenseSource"]');
    const dispensePrintEnabled = document.getElementById('dispensePrintEnabled');
    const showAllBtn = document.getElementById('showAllBtn');
    const showLowStockBtn = document.getElementById('showLowStockBtn');
    const locationFilterSelect = document.getElementById('locationFilterSelect');
    const userMenuBtn = document.getElementById('userMenuBtn');
    const adminBtn = document.getElementById('adminBtn');
    const locationsBtn = document.getElementById('locationsBtn');
    const reportsBtn = document.getElementById('reportsBtn');
    const logoutBtn = document.getElementById('logoutBtn');
    const changePasswordBtn = document.getElementById('changePasswordBtn');

    // Modal close buttons
    const closeButtons = document.querySelectorAll('.close');

    if (drugForm) drugForm.addEventListener('submit', handleAddDrug);

    // Auto-capitalise the first letter typed in each Add Drug text field
    ['drugName', 'drugDescription'].forEach(id => {
        const el = document.getElementById(id);
        if (el) el.addEventListener('input', () => {
            if (el.value.length === 1) el.value = el.value.toUpperCase();
        });
    });

    // Auto-capitalise the first letter typed in each Dispense text field
    ['dispenseAnimal', 'dispenseDosage', 'dispenseNotes'].forEach(id => {
        const el = document.getElementById(id);
        if (el) el.addEventListener('input', () => {
            if (el.value.length === 1) el.value = el.value.toUpperCase();
        });
    });

    const vetInput = document.getElementById('dispenseVet');
    if (vetInput) {
        vetInput.addEventListener('input', () => {
            const pos = vetInput.selectionStart;
            vetInput.value = toTitleCase(vetInput.value);
            vetInput.setSelectionRange(pos, pos);
        });
    }

    if (variantForm) variantForm.addEventListener('submit', handleAddVariant);
    if (editVariantForm) editVariantForm.addEventListener('submit', handleEditVariant);
    if (dispenseForm) dispenseForm.addEventListener('submit', handleDispenseDrug);
    if (editForm) editForm.addEventListener('submit', handleEditDrug);
    if (printNotesForm) printNotesForm.addEventListener('submit', handlePrintNotes);
    if (disposeBatchForm) disposeBatchForm.addEventListener('submit', handleDisposeBatch);
    
    const batchReceiveForm = document.getElementById('batchReceiveForm');
    if (batchReceiveForm) batchReceiveForm.addEventListener('submit', handleBatchReceive);
    if (cancelBatchReceiveBtn) cancelBatchReceiveBtn.addEventListener('click', () => closeModal(batchReceiveModal));

    const receiveDeliveryForm = document.getElementById('receiveDeliveryForm');
    if (receiveDeliveryForm) receiveDeliveryForm.addEventListener('submit', handleReceiveDelivery);
    if (cancelReceiveDeliveryBtn) cancelReceiveDeliveryBtn.addEventListener('click', () => {
        _detachDeliveryBarcodeListener();
        closeModal(receiveDeliveryModal);
    });
    if (addDeliveryLineBtn) addDeliveryLineBtn.addEventListener('click', () => appendDeliveryLine());
    if (addVariantFromDeliveryBtn) addVariantFromDeliveryBtn.addEventListener('click', handleAddVariantFromDelivery);
    if (addPackSizeFromDeliveryBtn) addPackSizeFromDeliveryBtn.addEventListener('click', openAddPackSizeFromDeliveryModal);

    const addPackSizeForm = document.getElementById('addPackSizeForm');
    const cancelAddPackSizeBtn = document.getElementById('cancelAddPackSizeBtn');
    const addPackSizeModal = document.getElementById('addPackSizeModal');
    if (addPackSizeForm) addPackSizeForm.addEventListener('submit', handleAddPackSize);
    if (cancelAddPackSizeBtn) cancelAddPackSizeBtn.addEventListener('click', () => closeModal(addPackSizeModal));

    const addPackSizeVariantSelect = document.getElementById('addPackSizeVariantSelect');
    if (addPackSizeVariantSelect) {
        addPackSizeVariantSelect.addEventListener('change', () => {
            const variantId = parseInt(addPackSizeVariantSelect.value || '', 10);
            const variant = getVariantById(variantId);
            const hint = document.getElementById('addPackSizeHint');
            if (hint) hint.textContent = variant ? `Base unit: ${variant.unit}` : '';
        });
    }
    if (addVariantPackRowBtn) addVariantPackRowBtn.addEventListener('click', () => appendVariantPackRow());
    if (addEditVariantPackRowBtn) addEditVariantPackRowBtn.addEventListener('click', () => appendEditVariantPackRow());
    if (variantUnitSelect) {
        variantUnitSelect.addEventListener('change', () => {
            refreshVariantPackRowLabels();
        });
    }
    if (editVariantUnitSelect) {
        editVariantUnitSelect.addEventListener('change', () => {
            refreshEditVariantPackRowLabels();
        });
    }
    if (variantStrengthInput && variantUnitSelect) {
        variantStrengthInput.addEventListener('blur', () => {
            variantUnitSelect.value = inferBaseUnitFromStrength(variantStrengthInput.value);
            refreshVariantPackRowLabels();
        });
    }
    dispenseModeInputs.forEach(input => input.addEventListener('change', updateDispenseModeUi));
    dispenseSourceInputs.forEach(input => input.addEventListener('change', () => {
        renderDispenseInventorySourceView();
        toggleDispensePrintFields();
        updateDispenseAllocationSummary();
    }));
    if (dispensePrintEnabled) {
        dispensePrintEnabled.addEventListener('change', toggleDispensePrintFields);
    }
    
    if (addDrugBtn) addDrugBtn.addEventListener('click', () => openModal(addModal));
    if (printNotesBtn) printNotesBtn.addEventListener('click', () => openModal(printNotesModal));
    if (receiveDeliveryBtn) receiveDeliveryBtn.addEventListener('click', openReceiveDeliveryModal);
    if (dispenseBtn) dispenseBtn.addEventListener('click', () => {
        updateDispenseDrugSelect();
        updateDispenseModeUi();
        openModal(dispenseModal);
    });
    
    if (cancelAddBtn) cancelAddBtn.addEventListener('click', () => closeModal(addModal));
    if (cancelVariantBtn) cancelVariantBtn.addEventListener('click', () => closeModal(addVariantModal));
    if (cancelEditVariantBtn) cancelEditVariantBtn.addEventListener('click', () => closeModal(editVariantModal));
    if (cancelDispenseBtn) cancelDispenseBtn.addEventListener('click', () => closeModal(dispenseModal));
    if (cancelEditBtn) cancelEditBtn.addEventListener('click', closeEditModal);
    if (cancelDisposeBatchBtn) cancelDisposeBatchBtn.addEventListener('click', closeDisposeBatchModal);
    
    const cancelPrintNotesBtn = document.getElementById('cancelPrintNotesBtn');
    if (cancelPrintNotesBtn) cancelPrintNotesBtn.addEventListener('click', () => closeModal(printNotesModal));
    
    const closeHistoryBtn = document.getElementById('closeHistoryBtn');
    if (closeHistoryBtn) closeHistoryBtn.addEventListener('click', () => closeModal(document.getElementById('historyModal')));

    const closeUserManagementBtn = document.getElementById('closeUserManagementBtn');
    if (closeUserManagementBtn) closeUserManagementBtn.addEventListener('click', () => closeModal(document.getElementById('userManagementModal')));
    
    const closeLocationManagementBtn = document.getElementById('closeLocationManagementBtn');
    if (closeLocationManagementBtn) closeLocationManagementBtn.addEventListener('click', () => closeModal(document.getElementById('locationManagementModal')));

    const createLocationForm = document.getElementById('createLocationForm');
    if (createLocationForm) createLocationForm.addEventListener('submit', createLocation);
    
    const changePasswordForm = document.getElementById('changePasswordForm');
    if (changePasswordForm) changePasswordForm.addEventListener('submit', handleChangePassword);
    
    const cancelChangePasswordBtn = document.getElementById('cancelChangePasswordBtn');
    if (cancelChangePasswordBtn) cancelChangePasswordBtn.addEventListener('click', () => closeModal(document.getElementById('changePasswordModal')));
    
    const adminChangePasswordForm = document.getElementById('adminChangePasswordForm');
    if (adminChangePasswordForm) adminChangePasswordForm.addEventListener('submit', handleAdminChangePassword);
    
    const cancelAdminChangePasswordBtn = document.getElementById('cancelAdminChangePasswordBtn');
    if (cancelAdminChangePasswordBtn) cancelAdminChangePasswordBtn.addEventListener('click', () => closeModal(document.getElementById('adminChangePasswordModal')));

    const cancelGtinMappingBtn = document.getElementById('cancelGtinMappingBtn');
    if (cancelGtinMappingBtn) cancelGtinMappingBtn.addEventListener('click', () => closeModal(document.getElementById('gtinMappingModal')));

    closeButtons.forEach(btn => btn.addEventListener('click', (e) => {
        const modal = e.target.closest('.modal');
        if (modal?.id === 'disposeBatchModal') {
            resetDisposeBatchModal();
        }
        if (modal?.id === 'receiveDeliveryModal') {
            _detachDeliveryBarcodeListener();
        }
        closeModal(modal);
    }));
    
    if (showAllBtn) showAllBtn.addEventListener('click', () => {
        showLowStockOnly = false;
        updateFilterButtons();
        renderDrugs();
    });
    if (showLowStockBtn) showLowStockBtn.addEventListener('click', () => {
        showLowStockOnly = true;
        updateFilterButtons();
        renderDrugs();
    });
    if (locationFilterSelect) locationFilterSelect.addEventListener('change', (e) => {
        selectedLocationFilter = e.target.value;
        renderDrugs();
    });
    
    // User menu
    if (userMenuBtn) userMenuBtn.addEventListener('click', (e) => {
        e.stopPropagation();
        const dropdown = document.getElementById('userDropdown');
        if (dropdown) {
            const isHidden = getComputedStyle(dropdown).display === 'none';
            dropdown.style.display = isHidden ? 'block' : 'none';
        }
    });

    document.addEventListener('click', (e) => {
        const dropdown = document.getElementById('userDropdown');
        const btn = document.getElementById('userMenuBtn');
        if (dropdown && btn && !btn.contains(e.target) && !dropdown.contains(e.target)) {
            dropdown.style.display = 'none';
        }
    });
    
    if (changePasswordBtn) changePasswordBtn.addEventListener('click', openChangePasswordModal);
    if (adminBtn) adminBtn.addEventListener('click', openUserManagement);
    if (locationsBtn) locationsBtn.addEventListener('click', openLocationManagement);
    if (reportsBtn) reportsBtn.addEventListener('click', openReportsPage);
    if (logoutBtn) logoutBtn.addEventListener('click', handleLogout);

    // Search functionality
    const drugSearch = document.getElementById('drugSearch');
    if (drugSearch) {
        let searchTimeout;
        drugSearch.addEventListener('input', (e) => {
            clearTimeout(searchTimeout);
            searchTimeout = setTimeout(() => {
                searchTerm = e.target.value.toLowerCase().trim();
                renderDrugs();
            }, 150);
        });
    }

    const dispenseQuantityInput = document.getElementById('dispenseQuantity');
    if (dispenseQuantityInput) {
        dispenseQuantityInput.addEventListener('input', () => {
            const mode = getSelectedDispenseMode();
            if (mode !== 'subunit') {
                return;
            }

            const packSelect = document.getElementById('dispensePackSelect');
            const packCount = document.getElementById('dispensePackCount');
            const packPreview = document.getElementById('dispensePackPreview');
            const variantId = parseInt(document.getElementById('dispenseDrugSelect')?.value || '', 10);
            const variant = getVariantById(variantId);

            if (packSelect) packSelect.value = '';
            if (packCount) packCount.value = '';
            if (packPreview && variant) {
                packPreview.textContent = `Enter direct quantity in ${variant.unit}.`;
            }

            autoAllocateDispenseBatches();
        });
    }

    // Close modal when clicking outside
    window.addEventListener('click', (e) => {
        if (e.target.classList.contains('modal')) {
            if (e.target.id === 'disposeBatchModal') {
                resetDisposeBatchModal();
            }
            closeModal(e.target);
        }
    });

    // Main-screen barcode scan
    document.addEventListener('keydown', _onMainScreenKeydown);
}

// Load drugs from API
async function loadDrugs() {
    try {
        const response = await apiCall('/drugs');
        if (!response.ok) throw new Error('Failed to load drugs');
        allDrugs = await response.json();

        updateLocationFilterOptions();
        renderDrugs();
        updateDispenseDrugSelect();

        if (_gtinMappingPendingRefresh) {
            _gtinMappingPendingRefresh = false;
            const restore = _gtinMappingPendingRestore || {};
            _gtinMappingPendingRestore = null;
            _gtinMappingPendingVariantId = null;

            // Resolve new variant by diffing (add-variant flow)
            if (restore._existingVariantIds && restore.drugId) {
                const drug = allDrugs.find(d => d.id === restore.drugId);
                const newVariant = drug?.variants?.find(v => !restore._existingVariantIds.has(v.id));
                if (newVariant) {
                    restore.variantId = newVariant.id;
                    // If no pack snapshot, all packs are new — pick the first active one from detail
                    if (!restore._existingPackIds) {
                        await ensureDrugDetailLoaded(restore.drugId);
                        const detailVariant = getVariantById(newVariant.id);
                        const firstPack = getActivePacksForVariant(detailVariant)?.[0];
                        if (firstPack) restore.packId = firstPack.id;
                    }
                }
            }
            // Resolve new pack by diffing (add-pack flow) — need packs from loaded detail
            if (restore._existingPackIds && restore.drugId && restore.variantId) {
                await ensureDrugDetailLoaded(restore.drugId);
                const variant = getVariantById(restore.variantId);
                const newPack = getActivePacksForVariant(variant)?.find(p => !restore._existingPackIds.has(p.id));
                if (newPack) restore.packId = newPack.id;
            }

            await _reinitGtinMappingModal(restore);
        }

        // After handleAddDrug's loadDrugs fires: find the newly created drug and set up
        // _gtinMappingPendingRefresh so that when handleAddVariant calls loadDrugs next,
        // we auto-select drug + new variant in the GTIN modal.
        if (_gtinMappingWaitingForNewDrug) {
            const newDrug = allDrugs.find(d => !_gtinMappingWaitingForNewDrug.has(d.id));
            _gtinMappingWaitingForNewDrug = null;
            if (newDrug) {
                // handleAddDrug will now open addVariantModal — prepare to catch that save
                _gtinMappingPendingRestore = {
                    drugId: newDrug.id,
                    variantId: null,
                    packId: null,
                    _existingVariantIds: new Set((newDrug.variants || []).map(v => v.id))
                };
                _gtinMappingPendingRefresh = true;
            }
        }
    } catch (error) {
        console.error('Error loading drugs:', error);
        document.getElementById('drugsList').innerHTML = 
            '<p class="empty">Error loading drugs. Make sure the backend is running.</p>';
    }
}

// Modal utility functions
function openModal(modal) {
    // Find the highest z-index among currently visible modals
    const visibleModals = document.querySelectorAll('.modal.show');
    let maxZIndex = 1000;
    
    visibleModals.forEach(m => {
        const zIndex = parseInt(window.getComputedStyle(m).zIndex, 10) || 1000;
        if (zIndex > maxZIndex) {
            maxZIndex = zIndex;
        }
    });
    
    // Set the new modal's z-index higher than any existing modal
    modal.style.zIndex = (maxZIndex + 100).toString();
    modal.classList.add('show');
    document.body.style.overflow = 'hidden';
}

function closeModal(modal) {
    modal.classList.remove('show');
    modal.style.zIndex = '1000';
    document.body.style.overflow = 'auto';
}

function closeEditModal() {
    closeModal(document.getElementById('editModal'));
}
function updateDispenseDrugSelect() {
    const select = document.getElementById('dispenseDrugSelect');
    select.innerHTML = '<option value="">-- Select a drug variant --</option>';
    
    allDrugs.forEach(drug => {
        drug.variants.forEach(variant => {
            const option = document.createElement('option');
            option.value = variant.id;
            option.textContent = `${drug.name} ${variant.strength} (${variant.quantity} ${variant.unit})`;
            select.appendChild(option);
        });
    });

    const packSelect = document.getElementById('dispensePackSelect');
    const packCount = document.getElementById('dispensePackCount');
    const packPreview = document.getElementById('dispensePackPreview');
    const quantityModeRadio = document.getElementById('dispenseModeQuantity');
    const batchSourceRadio = document.getElementById('dispenseSourceBatch');
    const legacySourceRadio = document.getElementById('dispenseSourceLegacy');
    if (packSelect) {
        packSelect.innerHTML = '<option value="">-- Select pack --</option>';
    }
    if (packCount) {
        packCount.value = '';
    }
    if (quantityModeRadio) {
        quantityModeRadio.checked = true;
    }
    if (packPreview) {
        packPreview.textContent = 'Select a pack and whole-number count.';
    }
    if (batchSourceRadio) {
        batchSourceRadio.checked = true;
    }
    if (legacySourceRadio) {
        legacySourceRadio.checked = false;
    }

    resetDispensePrintFields();

    currentDispenseBatches = [];
    currentDispenseLegacyQuantity = 0;

    updateDispenseModeUi();
}

function getSelectedDispenseMode() {
    return document.querySelector('input[name="dispenseMode"]:checked')?.value || 'subunit';
}

function hasLegacyDispenseQuantity() {
    return currentDispenseLegacyQuantity > 0;
}

function hasBatchDispenseStock() {
    return currentDispenseBatches.length > 0;
}

function getSelectedDispenseSource() {
    if (getSelectedDispenseMode() === 'pack') {
        return 'batch';
    }

    const selected = document.querySelector('input[name="dispenseSource"]:checked')?.value;
    if (selected) {
        return selected;
    }

    if (hasLegacyDispenseQuantity() && !hasBatchDispenseStock()) {
        return 'legacy';
    }

    return 'batch';
}

function isLegacyDispenseSelected() {
    return getSelectedDispenseMode() === 'subunit' && getSelectedDispenseSource() === 'legacy' && hasLegacyDispenseQuantity();
}

function updateDispenseSourceUi() {
    const sourceGroup = document.getElementById('dispenseSourceGroup');
    const sourceHelp = document.getElementById('dispenseSourceHelp');
    const batchRadio = document.getElementById('dispenseSourceBatch');
    const legacyRadio = document.getElementById('dispenseSourceLegacy');
    const hasBatches = hasBatchDispenseStock();
    const hasLegacy = hasLegacyDispenseQuantity();

    if (!sourceGroup || !batchRadio || !legacyRadio) {
        return;
    }

    if (getSelectedDispenseMode() === 'pack' || (!hasBatches && !hasLegacy)) {
        sourceGroup.style.display = 'none';
        batchRadio.checked = true;
        batchRadio.disabled = !hasBatches;
        legacyRadio.checked = false;
        legacyRadio.disabled = true;
        if (sourceHelp) sourceHelp.textContent = '';
        return;
    }

    batchRadio.disabled = !hasBatches;
    legacyRadio.disabled = !hasLegacy;

    if (hasLegacy && !hasBatches) {
        legacyRadio.checked = true;
    } else if (!hasLegacy && hasBatches) {
        batchRadio.checked = true;
    } else if (!batchRadio.checked && !legacyRadio.checked) {
        batchRadio.checked = true;
    }

    sourceGroup.style.display = hasLegacy ? '' : 'none';
    if (sourceHelp) {
        if (hasLegacy && hasBatches) {
            sourceHelp.textContent = `Batch stock available alongside ${formatDisplayNumber(currentDispenseLegacyQuantity)} loose legacy units.`;
        } else if (hasLegacy) {
            sourceHelp.textContent = `Legacy loose stock available: ${formatDisplayNumber(currentDispenseLegacyQuantity)}.`;
        } else {
            sourceHelp.textContent = '';
        }
    }
}

function toggleDispensePrintFields() {
    const printEnabled = document.getElementById('dispensePrintEnabled');
    const printFields = document.getElementById('dispensePrintFields');
    const printHelpText = document.getElementById('dispensePrintHelpText');
    const dosageInput = document.getElementById('dispenseDosage');
    const legacyExpiryGroup = document.getElementById('dispenseLegacyExpiryGroup');
    const legacyExpiryInput = document.getElementById('dispenseLegacyExpiry');
    const isEnabled = Boolean(printEnabled?.checked);
    const legacyStockOnly = isLegacyDispenseSelected();

    if (printFields) {
        printFields.style.display = isEnabled ? '' : 'none';
    }
    if (printHelpText) {
        printHelpText.textContent = legacyStockOnly
            ? 'Uses the dispensed quantity, the animal name/ID entered above, the logged-in user, and a manually entered expiry date for this legacy stock.'
            : 'Uses the dispensed quantity, the animal name/ID entered above, the logged-in user, and the latest expiry date from the allocated batches.';
    }
    if (dosageInput) {
        dosageInput.required = isEnabled;
    }
    if (legacyExpiryGroup) {
        legacyExpiryGroup.style.display = isEnabled && legacyStockOnly ? '' : 'none';
    }
    if (legacyExpiryInput) {
        legacyExpiryInput.required = isEnabled && legacyStockOnly;
        if (!legacyStockOnly) {
            legacyExpiryInput.value = '';
        }
    }
}

function resetDispensePrintFields() {
    const printEnabled = document.getElementById('dispensePrintEnabled');
    const dosageInput = document.getElementById('dispenseDosage');
    const legacyExpiryInput = document.getElementById('dispenseLegacyExpiry');

    if (printEnabled) {
        printEnabled.checked = false;
    }
    if (dosageInput) {
        dosageInput.value = '';
    }
    if (legacyExpiryInput) {
        legacyExpiryInput.value = '';
    }

    toggleDispensePrintFields();
}

function formatLabelExpiryDate(expiryDate) {
    const expiryParts = expiryDate.split('-');
    return `${expiryParts[2]}/${expiryParts[1]}/${expiryParts[0]}`;
}

function getDrugContextForVariant(variantId) {
    for (const drug of allDrugs) {
        const variant = (drug.variants || []).find(item => item.id === variantId);
        if (variant) {
            return { drug, variant };
        }
    }
    return { drug: null, variant: null };
}

function getLatestAllocatedBatchExpiryDate(allocationEntries) {
    const allocatedBatches = allocationEntries
        .map(entry => currentDispenseBatches.find(batch => batch.id === entry.batch_id))
        .filter(batch => batch?.expiry_date);

    if (allocatedBatches.length === 0) {
        return null;
    }

    return allocatedBatches
        .map(batch => batch.expiry_date)
        .sort((left, right) => new Date(right) - new Date(left))[0];
}

async function requestLabelPrint({ animalName, drugName, variantStrength, quantity, unit, dosage, expiryDate }) {
    const labelData = {
        variables: {
            practice_name: 'Many Tears Animal Rescue',
            animal_name: animalName,
            drug_name: `${drugName} ${variantStrength}`,
            dosage,
            quantity: `${quantity} ${unit}`,
            expiry_date: formatLabelExpiryDate(expiryDate)
        }
    };

    const labelResponse = await apiCall('/labels/print', {
        method: 'POST',
        body: JSON.stringify(labelData)
    });

    if (!labelResponse.ok) {
        const error = await labelResponse.json();
        throw new Error(error.detail || 'Label printing request failed');
    }

    return labelResponse.json();
}

function populateDispensePackSelect(variant) {
    const packSelect = document.getElementById('dispensePackSelect');
    const packCount = document.getElementById('dispensePackCount');
    const packPreview = document.getElementById('dispensePackPreview');
    if (!packSelect) return;

    const activePacks = getActivePacksForVariant(variant);
    packSelect.innerHTML = '<option value="">-- Select pack --</option>';

    activePacks.forEach(pack => {
        const option = document.createElement('option');
        option.value = String(pack.id);
        option.textContent = `${packLabel(pack)} (${pack.pack_size_in_base_units} ${variant.unit})`;
        packSelect.appendChild(option);
    });

    if (packCount) packCount.value = '';

    // Auto-select the first available pack
    if (activePacks.length > 0) {
        packSelect.value = String(activePacks[0].id);
    }

    if (packPreview) {
        packPreview.textContent = activePacks.length > 0
            ? `Select a pack and whole-number count (${variant.unit} base unit).`
            : `No active packs for this variant.`;
    }

    // Update preview to reflect the auto-selected pack
    if (activePacks.length > 0) {
        updateDispenseQuantityFromPack();
    }
}

function updateDispenseModeUi() {
    const mode = getSelectedDispenseMode();
    const quantityGroup = document.getElementById('dispenseQuantityGroup');
    const packRow = document.getElementById('dispensePackRow');
    const quantityInput = document.getElementById('dispenseQuantity');
    const packSelect = document.getElementById('dispensePackSelect');
    const packCount = document.getElementById('dispensePackCount');

    if (quantityGroup) {
        quantityGroup.style.display = mode === 'subunit' ? '' : 'none';
    }
    if (packRow) {
        packRow.style.display = mode === 'pack' ? '' : 'none';
    }

    if (quantityInput) {
        quantityInput.required = mode === 'subunit';
    }
    if (packSelect) {
        packSelect.required = mode === 'pack';
    }
    if (packCount) {
        packCount.required = mode === 'pack';
    }

    updateDispenseSourceUi();
    renderDispenseInventorySourceView();
    toggleDispensePrintFields();
}

function updateDispenseQuantityFromPack() {
    const mode = getSelectedDispenseMode();
    if (mode !== 'pack') return;

    const variantId = parseInt(document.getElementById('dispenseDrugSelect')?.value || '', 10);
    const packId = parseInt(document.getElementById('dispensePackSelect')?.value || '', 10);
    const packCount = parseFloat(document.getElementById('dispensePackCount')?.value || '');
    const quantityInput = document.getElementById('dispenseQuantity');
    const preview = document.getElementById('dispensePackPreview');

    const variant = getVariantById(variantId);
    if (!quantityInput || !preview || !variant) return;

    const selectedPack = getActivePacksForVariant(variant).find(pack => pack.id === packId);
    const totalAvailablePacks = selectedPack ? getTotalAvailableDispensePackCount(selectedPack) : 0;
    if (selectedPack && !Number.isNaN(packCount) && packCount > 0) {
        if (Math.abs(packCount - Math.round(packCount)) > 1e-6) {
            preview.textContent = 'Whole-pack mode requires a whole-number pack count.';
            return;
        }
        if (totalAvailablePacks <= 0) {
            quantityInput.value = String(packCount * selectedPack.pack_size_in_base_units);
            preview.textContent = `No full ${selectedPack.pack_unit_name} packs are currently available.`;
            autoAllocateDispenseBatches();
            return;
        }
        if (packCount > totalAvailablePacks) {
            quantityInput.value = String(packCount * selectedPack.pack_size_in_base_units);
            preview.textContent = `Only ${totalAvailablePacks} full ${selectedPack.pack_unit_name} pack${totalAvailablePacks === 1 ? '' : 's'} available.`;
            autoAllocateDispenseBatches();
            return;
        }
        const quantity = packCount * selectedPack.pack_size_in_base_units;
        quantityInput.value = String(quantity);
        preview.textContent = `${packCount} × ${selectedPack.pack_size_in_base_units} = ${quantity} ${variant.unit} | ${totalAvailablePacks} full pack${totalAvailablePacks === 1 ? '' : 's'} available`;
        autoAllocateDispenseBatches();
        return;
    }

    preview.textContent = selectedPack
        ? `${totalAvailablePacks} full ${selectedPack.pack_unit_name} pack${totalAvailablePacks === 1 ? '' : 's'} available | 1 ${selectedPack.pack_unit_name} = ${selectedPack.pack_size_in_base_units} ${variant.unit}`
        : `Select a pack to calculate quantity.`;
    autoAllocateDispenseBatches();
}

function formatDisplayDate(value) {
    if (!value) {
        return 'Unknown';
    }

    const parsed = new Date(value);
    if (Number.isNaN(parsed.getTime())) {
        return value;
    }

    return parsed.toLocaleDateString();
}

function formatDisplayNumber(value) {
    const numeric = Number(value);
    if (Number.isNaN(numeric)) return '0';
    return Number.isInteger(numeric) ? String(numeric) : String(Number(numeric.toFixed(3)));
}

function isBatchExpired(batch) {
    if (!batch?.expiry_date) {
        return false;
    }

    const today = new Date();
    today.setHours(0, 0, 0, 0);
    const expiryDate = new Date(`${batch.expiry_date}T00:00:00`);
    return expiryDate < today;
}

function renderVariantInventoryDetails(variant, batches) {
    const activePacks = getActivePacksForVariant(variant);
    const isReadOnly = currentUser?.role === 'readonly';
    const sortedBatches = [...(batches || [])]
        .filter(batch => Number(batch.quantity) > 0)
        .sort((a, b) => new Date(a.expiry_date) - new Date(b.expiry_date));

    const packsHtml = activePacks.length > 0
        ? activePacks.map(pack => `
            <div style="padding: 6px 8px; background: #ffffff; border: 1px solid #d8e2ea; border-radius: 5px; font-size: 0.9em;">
                <strong>${escapeHtml(packLabel(pack))}</strong>
                <span style="color: #4b5563;"> (${formatDisplayNumber(pack.pack_size_in_base_units)} ${escapeHtml(variant.unit)})</span>
            </div>
        `).join('')
        : '<div style="padding: 6px 8px; background: #ffffff; border: 1px dashed #cfd8e3; border-radius: 5px; font-size: 0.9em; color: #6b7280;">No active packs configured</div>';

    const batchesHtml = sortedBatches.length > 0
        ? sortedBatches.map(batch => {
            const locationLabel = getBatchLocationLabel(batch);
            const expired = isBatchExpired(batch);
            const hasPackState = batch.current_full_pack_count != null && batch.current_loose_base_units != null && batch.received_pack_unit_name;
            const stocktakeLabel = hasPackState
                ? `${formatDisplayNumber(batch.current_full_pack_count)} full ${escapeHtml(packLabel(batch.received_pack_unit_name, batch.received_pack_size_snapshot))} + ${formatDisplayNumber(batch.current_loose_base_units)} ${escapeHtml(variant.unit)} loose`
                : `${formatDisplayNumber(batch.quantity)} ${escapeHtml(variant.unit)}`;
            const isHighlighted = _highlightedBatchLot === batch.batch_number && _highlightedVariantId === variant.id;
            const batchCardStyles = isHighlighted
                ? 'padding: 8px; background: #fef9c3; border: 2px solid #f59e0b; border-radius: 5px; font-size: 0.9em;'
                : expired
                    ? 'padding: 8px; background: #fff1f2; border: 1px solid #f3a6ad; border-radius: 5px; font-size: 0.9em;'
                    : 'padding: 8px; background: #ffffff; border: 1px solid #d8e2ea; border-radius: 5px; font-size: 0.9em;';
            const expiryStyles = expired ? 'color: #b91c1c; font-weight: 700;' : 'color: #4b5563;';

            return `
                <div style="${batchCardStyles}" data-batch-number="${escapeHtml(batch.batch_number)}" data-variant-id="${variant.id}">
                    <div style="display: flex; justify-content: space-between; gap: 8px; flex-wrap: wrap;">
                        <div style="display: flex; align-items: center; gap: 8px; flex-wrap: wrap;">
                            <strong>${escapeHtml(batch.batch_number)}</strong>
                            ${expired ? '<span style="background: #b91c1c; color: white; padding: 2px 6px; border-radius: 999px; font-size: 0.75em; font-weight: 700;">Expired</span>' : ''}
                        </div>
                        <span style="${expiryStyles}">Expires ${formatDisplayDate(batch.expiry_date)}</span>
                    </div>
                    <div style="margin-top: 4px; color: #374151;">${escapeHtml(locationLabel)} | ${stocktakeLabel}</div>
                    ${expired && !isReadOnly ? `
                        <div style="margin-top: 8px; display: flex; justify-content: flex-end;">
                            <button class="btn btn-danger btn-small" onclick="event.stopPropagation(); disposeBatch(${batch.id}, '${String(batch.batch_number).replace(/'/g, "\\'")}')">Dispose Expired Batch</button>
                        </div>
                    ` : ''}
                </div>
            `;
        }).join('')
        : '<div style="padding: 6px 8px; background: #ffffff; border: 1px dashed #cfd8e3; border-radius: 5px; font-size: 0.9em; color: #6b7280;">No active batches</div>';

    return `
        <div style="margin-top: 10px; background: #f2f6fa; border: 1px solid #d6e0ea; border-radius: 8px; padding: 10px;" onclick="event.stopPropagation()">
            <div style="display: grid; grid-template-columns: 1fr 1fr; gap: 12px;">
                <div>
                    <div style="font-size: 0.8em; text-transform: uppercase; letter-spacing: 0.04em; color: #4b5563; margin-bottom: 6px;">Active Packs</div>
                    <div style="display: grid; gap: 6px;">${packsHtml}</div>
                </div>
                <div>
                    <div style="font-size: 0.8em; text-transform: uppercase; letter-spacing: 0.04em; color: #4b5563; margin-bottom: 6px;">Current Batches</div>
                    <div style="display: grid; gap: 6px;">${batchesHtml}</div>
                </div>
            </div>
        </div>
    `;
}

function disposeBatch(batchId, batchNumber) {
    const modal = document.getElementById('disposeBatchModal');
    const batchIdInput = document.getElementById('disposeBatchId');
    const batchNameInput = document.getElementById('disposeBatchName');
    const notesInput = document.getElementById('disposeBatchNotes');

    if (!modal || !batchIdInput || !batchNameInput || !notesInput) {
        showToast('Dispose batch modal is unavailable.', 'error');
        return;
    }

    batchIdInput.value = String(batchId);
    batchNameInput.value = batchNumber;
    notesInput.value = '';
    openModal(modal);
}

async function handleDisposeBatch(e) {
    e.preventDefault();

    const batchId = parseInt(document.getElementById('disposeBatchId')?.value || '', 10);
    const notes = document.getElementById('disposeBatchNotes')?.value.trim() || '';
    const modal = document.getElementById('disposeBatchModal');

    if (!batchId) {
        showToast('Batch disposal context is unavailable.', 'error');
        return;
    }

    try {
        const response = await apiCall(`/batches/${batchId}/dispose`, {
            method: 'POST',
            body: JSON.stringify({ notes: notes || null })
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to dispose batch');
        }

        if (modal) {
            closeDisposeBatchModal();
        }
        // Find which variant this batch belongs to and invalidate its batch cache
        const batchVariantId = (() => {
            for (const [vid, batches] of loadedVariantBatches) {
                if (batches.some(b => b.id === batchId)) return vid;
            }
            return null;
        })();
        if (batchVariantId) {
            loadedVariantBatches.delete(batchVariantId);
        }
        await loadDrugs();
        showToast('Expired batch marked as disposed.', 'success');
    } catch (error) {
        console.error('Error disposing batch:', error);
        showToast('Failed to dispose batch: ' + error.message, 'error');
    }
}

function getBatchLocationLabel(batch) {
    return batch.location_name || batch.location?.name || `Location #${batch.location_id}`;
}

function updateLocationFilterOptions() {
    const locationFilterSelect = document.getElementById('locationFilterSelect');
    if (!locationFilterSelect) return;

    const previousValue = selectedLocationFilter;
    const locations = new Set();

    allDrugs.forEach(drug => {
        (drug.locations || []).forEach(loc => locations.add(loc));
    });

    locationFilterSelect.innerHTML = '<option value="">All Locations</option>';
    Array.from(locations)
        .sort((a, b) => a.localeCompare(b))
        .forEach(location => {
            const option = document.createElement('option');
            option.value = location;
            option.textContent = location;
            locationFilterSelect.appendChild(option);
        });

    if (previousValue && locations.has(previousValue)) {
        selectedLocationFilter = previousValue;
        locationFilterSelect.value = previousValue;
    } else {
        selectedLocationFilter = '';
        locationFilterSelect.value = '';
    }
}

function getDispenseRequestedQuantity() {
    const quantity = parseFloat(document.getElementById('dispenseQuantity')?.value || '');
    return Number.isNaN(quantity) || quantity <= 0 ? 0 : quantity;
}

function getSelectedDispensePack() {
    const variantId = parseInt(document.getElementById('dispenseDrugSelect')?.value || '', 10);
    const packId = parseInt(document.getElementById('dispensePackSelect')?.value || '', 10);
    const variant = getVariantById(variantId);
    if (!variant || Number.isNaN(packId)) {
        return null;
    }

    return getActivePacksForVariant(variant).find(pack => pack.id === packId) || null;
}

function batchMatchesSelectedPack(batch, selectedPack) {
    if (!batch || !selectedPack) {
        return false;
    }

    if (Number(batch.received_pack_id) === Number(selectedPack.id)) {
        return true;
    }

    const batchPackLabel = String(batch.received_pack_unit_name || '').trim().toLowerCase();
    const selectedPackLabel = String(selectedPack.pack_unit_name || '').trim().toLowerCase();
    if (batchPackLabel && selectedPackLabel && batchPackLabel === selectedPackLabel) {
        return true;
    }

    const batchPackSize = Number(batch.received_pack_size_snapshot || 0);
    const selectedPackSize = Number(selectedPack.pack_size_in_base_units || 0);
    if (batchPackSize > 0 && selectedPackSize > 0 && Math.abs(batchPackSize - selectedPackSize) <= 1e-6) {
        return true;
    }

    return false;
}

function getBatchAvailableDispenseQuantity(batch, mode = getSelectedDispenseMode(), selectedPack = getSelectedDispensePack()) {
    if (mode !== 'pack') {
        return Number(batch.quantity || 0);
    }

    if (!batchMatchesSelectedPack(batch, selectedPack)) {
        return 0;
    }

    const fullPackCount = Math.max(0, Math.floor(Number(batch.current_full_pack_count || 0)));
    return fullPackCount * Number(selectedPack.pack_size_in_base_units || 0);
}

function getTotalAvailableDispenseQuantity(mode = getSelectedDispenseMode(), selectedPack = getSelectedDispensePack()) {
    if (getSelectedDispenseSource() === 'legacy') {
        return mode === 'pack' ? 0 : currentDispenseLegacyQuantity;
    }
    return currentDispenseBatches.reduce((sum, batch) => sum + getBatchAvailableDispenseQuantity(batch, mode, selectedPack), 0);
}

function getTotalAvailableDispensePackCount(selectedPack = getSelectedDispensePack()) {
    if (getSelectedDispenseSource() === 'legacy') {
        return 0;
    }
    if (!selectedPack) {
        return 0;
    }

    return currentDispenseBatches.reduce((sum, batch) => {
        if (!batchMatchesSelectedPack(batch, selectedPack)) {
            return sum;
        }
        return sum + Math.max(0, Math.floor(Number(batch.current_full_pack_count || 0)));
    }, 0);
}

function renderDispenseBatchAllocationRows(activeBatches) {
    const batchInfoContent = document.getElementById('batchInfoContent');
    const variantId = parseInt(document.getElementById('dispenseDrugSelect').value || '', 10);
    const variant = getVariantById(variantId);
    const unitLabel = variant?.unit || 'units';

    if (!batchInfoContent) return;

    if (!activeBatches.length) {
        batchInfoContent.innerHTML = '<p style="color: #d32f2f; margin: 0;">⚠️ No active batches available for this variant</p>';
        return;
    }

    const mode = getSelectedDispenseMode();
    const selectedPack = getSelectedDispensePack();

    batchInfoContent.innerHTML = activeBatches.map((batch, index) => {
        const expiryDate = new Date(batch.expiry_date);
        const locationLabel = getBatchLocationLabel(batch);
        const expiryLabel = formatDisplayDate(batch.expiry_date);
        const today = new Date();
        const isExpired = expiryDate < today;
        const daysToExpiry = Math.ceil((expiryDate - today) / (1000 * 60 * 60 * 24));

        let expiryStatus = 'OK';
        let statusColor = '#4caf50';
        if (isExpired) {
            expiryStatus = 'EXPIRED';
            statusColor = '#d32f2f';
        } else if (daysToExpiry <= 7) {
            expiryStatus = `${daysToExpiry}d left`;
            statusColor = '#ff9800';
        }

        const availableFullPacks = batchMatchesSelectedPack(batch, selectedPack)
            ? Math.max(0, Math.floor(Number(batch.current_full_pack_count || 0)))
            : 0;
        const allocationLabel = mode === 'pack' ? 'Allocate Packs' : 'Allocate';
        const allocationMax = mode === 'pack' ? availableFullPacks : getBatchAvailableDispenseQuantity(batch, mode, selectedPack);
        const allocationStep = mode === 'pack' ? 1 : 0.1;
        const batchAvailabilityNote = mode === 'pack'
            ? (selectedPack && batchMatchesSelectedPack(batch, selectedPack) && availableFullPacks <= 0
                ? 'No full packs available in this batch'
                : '')
            : `Available to allocate: ${formatDisplayNumber(batch.quantity)} ${escapeHtml(unitLabel)}`;

        return `
            <div style="padding: 10px; margin: 6px 0; background: white; border: 1px solid #e0e0e0; border-radius: 4px; ${index === 0 ? 'border-left: 3px solid #2196F3; background: #f8fbff;' : ''}">
                <div style="display: grid; grid-template-columns: minmax(0, 1.8fr) minmax(0, 1fr) 140px; gap: 12px; align-items: end;">
                    <div>
                        <div><strong>${escapeHtml(batch.batch_number)}</strong>${index === 0 ? ' <span style="background: #2196F3; color: white; padding: 2px 6px; border-radius: 2px; font-size: 0.8em; margin-left: 5px;">FEFO</span>' : ''}</div>
                        <div style="font-size: 0.9em; color: #666; margin-top: 4px;">
                            Available: <strong>${formatDisplayNumber(batch.quantity)} ${escapeHtml(unitLabel)}</strong> |
                            Location: <strong>${escapeHtml(locationLabel)}</strong> |
                            Expiry: <strong>${expiryLabel}</strong> <span style="color: ${statusColor};">(${expiryStatus})</span>
                        </div>
                    </div>
                    <div style="font-size: 0.9em; color: #374151;">
                        ${batch.current_full_pack_count != null && batch.current_loose_base_units != null && batch.received_pack_unit_name
                            ? `Stock: ${formatDisplayNumber(batch.current_full_pack_count)} full ${escapeHtml(packLabel(batch.received_pack_unit_name, batch.received_pack_size_snapshot))} + ${formatDisplayNumber(batch.current_loose_base_units)} ${escapeHtml(unitLabel)} loose`
                            : ''}
                        ${batchAvailabilityNote ? `<div style="margin-top: 4px; color: #d32f2f;">${batchAvailabilityNote}</div>` : ''}
                    </div>
                    <div class="form-group" style="margin-bottom: 0;">
                        <label for="dispenseBatchAllocation-${batch.id}">${allocationLabel}</label>
                        <input
                            type="number"
                            id="dispenseBatchAllocation-${batch.id}"
                            class="dispense-batch-allocation"
                            data-batch-id="${batch.id}"
                            data-allocation-mode="${mode}"
                            data-pack-size="${mode === 'pack' && selectedPack ? selectedPack.pack_size_in_base_units : ''}"
                            min="0"
                            max="${allocationMax}"
                            step="${allocationStep}"
                            value="0"
                        >
                    </div>
                </div>
            </div>
        `;
    }).join('');

    batchInfoContent.querySelectorAll('.dispense-batch-allocation').forEach(input => {
        input.addEventListener('input', updateDispenseAllocationSummary);
    });
}

function renderExpiredDispenseBatches(expiredBatches) {
    const expiredDetails = document.getElementById('expiredBatchDetails');
    const expiredContent = document.getElementById('expiredBatchContent');
    const variantId = parseInt(document.getElementById('dispenseDrugSelect').value || '', 10);
    const variant = getVariantById(variantId);
    const unitLabel = variant?.unit || 'units';

    if (!expiredDetails || !expiredContent) {
        return;
    }

    if (!expiredBatches.length) {
        expiredDetails.style.display = 'none';
        expiredDetails.open = false;
        expiredContent.innerHTML = '';
        return;
    }

    expiredDetails.style.display = 'block';
    expiredContent.innerHTML = expiredBatches.map(batch => {
        const locationLabel = getBatchLocationLabel(batch);
        const expiryLabel = formatDisplayDate(batch.expiry_date);
        const stocktakeLabel = batch.current_full_pack_count != null && batch.current_loose_base_units != null && batch.received_pack_unit_name
            ? `${formatDisplayNumber(batch.current_full_pack_count)} full ${escapeHtml(packLabel(batch.received_pack_unit_name, batch.received_pack_size_snapshot))} + ${formatDisplayNumber(batch.current_loose_base_units)} ${escapeHtml(unitLabel)} loose`
            : `${formatDisplayNumber(batch.quantity)} ${escapeHtml(unitLabel)}`;

        return `
            <div style="padding: 8px; margin: 6px 0; background: white; border: 1px solid #f0d7a1; border-radius: 4px;">
                <div style="display: flex; justify-content: space-between; gap: 8px; flex-wrap: wrap;">
                    <strong>${escapeHtml(batch.batch_number)}</strong>
                    <span style="color: #b45309; font-weight: 600;">Expired ${expiryLabel}</span>
                </div>
                <div style="font-size: 0.9em; color: #666; margin-top: 4px;">
                    Qty: <strong>${formatDisplayNumber(batch.quantity)} ${escapeHtml(unitLabel)}</strong> |
                    Location: <strong>${escapeHtml(locationLabel)}</strong>
                </div>
                <div style="font-size: 0.9em; color: #374151; margin-top: 4px;">${stocktakeLabel}</div>
            </div>
        `;
    }).join('');
}

function renderDispenseInventorySourceView() {
    const batchInfoContent = document.getElementById('batchInfoContent');
    const variantId = parseInt(document.getElementById('dispenseDrugSelect')?.value || '', 10);
    const variant = getVariantById(variantId);

    if (!batchInfoContent || !variant) {
        return;
    }

    if (getSelectedDispenseMode() === 'pack') {
        if (hasBatchDispenseStock()) {
            renderDispenseBatchAllocationRows(currentDispenseBatches);
            autoAllocateDispenseBatches();
        } else if (hasLegacyDispenseQuantity()) {
            batchInfoContent.innerHTML = `<div style="padding: 10px; background: #fff8e8; border: 1px solid #f3d18d; border-radius: 4px; color: #7a4f01;"><strong>Legacy stock only.</strong> ${formatDisplayNumber(currentDispenseLegacyQuantity)} ${escapeHtml(variant.unit || 'units')} available outside the batch system. Whole-pack dispensing is unavailable.</div>`;
            updateDispenseAllocationSummary();
        } else {
            batchInfoContent.innerHTML = '<p style="color: #d32f2f; margin: 0;">⚠️ No active batches available for this variant</p>';
            updateDispenseAllocationSummary();
        }
        return;
    }

    if (isLegacyDispenseSelected()) {
        const extraText = hasBatchDispenseStock() ? ' Batch stock is also available; switch source to allocate from batches.' : ' Dispense by quantity only.';
        batchInfoContent.innerHTML = `<div style="padding: 10px; background: #fff8e8; border: 1px solid #f3d18d; border-radius: 4px; color: #7a4f01;"><strong>Legacy loose stock selected.</strong> ${formatDisplayNumber(currentDispenseLegacyQuantity)} ${escapeHtml(variant.unit || 'units')} available outside the batch system.${extraText}</div>`;
        updateDispenseAllocationSummary();
        return;
    }

    if (hasBatchDispenseStock()) {
        renderDispenseBatchAllocationRows(currentDispenseBatches);
        autoAllocateDispenseBatches();
        return;
    }

    if (hasLegacyDispenseQuantity()) {
        batchInfoContent.innerHTML = `<div style="padding: 10px; background: #fff8e8; border: 1px solid #f3d18d; border-radius: 4px; color: #7a4f01;"><strong>Legacy stock only.</strong> ${formatDisplayNumber(currentDispenseLegacyQuantity)} ${escapeHtml(variant.unit || 'units')} available outside the batch system. Dispense by quantity only.</div>`;
        updateDispenseAllocationSummary();
        return;
    }

    batchInfoContent.innerHTML = '<p style="color: #d32f2f; margin: 0;">⚠️ No active batches available for this variant</p>';
    updateDispenseAllocationSummary();
}

// Update batch info display when variant is selected
async function updateBatchInfo() {
    const variantId = parseInt(document.getElementById('dispenseDrugSelect').value);
    const batchInfoSection = document.getElementById('batchInfoSection');
    const batchInfoContent = document.getElementById('batchInfoContent');
    
    if (!variantId) {
        batchInfoSection.style.display = 'none';
        const packSelect = document.getElementById('dispensePackSelect');
        if (packSelect) packSelect.innerHTML = '<option value="">-- Select pack --</option>';
        currentDispenseBatches = [];
        currentDispenseLegacyQuantity = 0;
        renderExpiredDispenseBatches([]);
        updateDispenseSourceUi();
        toggleDispensePrintFields();
        updateDispenseAllocationSummary();
        return;
    }

    const variant = getVariantById(variantId);
    if (variant) {
        // Ensure drug detail (with packs) is loaded before populating pack select
        const drugOfVariant = allDrugs.find(d => (d.variants || []).some(v => v.id === variantId));
        if (drugOfVariant) await ensureDrugDetailLoaded(drugOfVariant.id);
        populateDispensePackSelect(getVariantById(variantId));

        const vetLabel = document.getElementById('dispenseVetLabel');
        const vetInputEl = document.getElementById('dispenseVet');
        if (vetLabel && vetInputEl) {
            const isControlled = drugOfVariant ? drugOfVariant.is_controlled : false;
            vetLabel.textContent = isControlled ? 'Prescribing Vet *' : 'Prescribing Vet';
            vetLabel.style.color = isControlled ? '#d32f2f' : '';
            vetInputEl.placeholder = isControlled ? "Vet's name (required)" : "Vet's name";
        }
    } else {
        const vetLabel = document.getElementById('dispenseVetLabel');
        const vetInputEl = document.getElementById('dispenseVet');
        if (vetLabel) { vetLabel.textContent = 'Prescribing Vet'; vetLabel.style.color = ''; }
        if (vetInputEl) vetInputEl.placeholder = "Vet's name";
    }
    updateDispenseModeUi();
    
    batchInfoSection.style.display = 'block';
    batchInfoContent.innerHTML = '<p class="loading">Loading batches...</p>';
    renderExpiredDispenseBatches([]);
    
    try {
        const response = await apiCall(`/variants/${variantId}/batches`);
        if (!response.ok) throw new Error('Failed to load batches');
        
        const batches = await response.json();
        
        const stockedBatches = batches.filter(b => b.quantity > 0);
        const expiredBatches = stockedBatches.filter(isBatchExpired);
        const activeBatches = stockedBatches.filter(batch => !isBatchExpired(batch));
        const totalBatchQuantity = stockedBatches.reduce((sum, batch) => sum + Number(batch.quantity || 0), 0);
        currentDispenseLegacyQuantity = Math.max(0, Number(variant?.quantity || 0) - totalBatchQuantity);
        currentDispenseBatches = activeBatches;
        renderExpiredDispenseBatches(expiredBatches);

        if (!activeBatches.length && currentDispenseLegacyQuantity <= 0 && expiredBatches.length > 0) {
            updateDispenseSourceUi();
            batchInfoContent.innerHTML = '<p style="color: #d32f2f; margin: 0;">⚠️ No in-date batches available for this variant. Expired batches are hidden from selection.</p>';
            toggleDispensePrintFields();
            updateDispenseAllocationSummary();
            return;
        }

        // Sort by expiry date (FEFO order)
        activeBatches.sort((a, b) => new Date(a.expiry_date) - new Date(b.expiry_date));
        currentDispenseBatches = activeBatches;
        updateDispenseSourceUi();
        renderDispenseInventorySourceView();
        toggleDispensePrintFields();
    } catch (error) {
        console.error('Error loading batches:', error);
        batchInfoContent.innerHTML = '<p style="color: #d32f2f; margin: 0;">Error loading batches</p>';
        currentDispenseBatches = [];
        currentDispenseLegacyQuantity = 0;
        renderExpiredDispenseBatches([]);
        updateDispenseSourceUi();
        toggleDispensePrintFields();
        updateDispenseAllocationSummary();
    }
}

function autoAllocateDispenseBatches() {
    const requestedQuantity = getDispenseRequestedQuantity();
    const allocationInputs = Array.from(document.querySelectorAll('.dispense-batch-allocation'));
    const mode = getSelectedDispenseMode();
    const selectedPack = getSelectedDispensePack();

    if (!allocationInputs.length) {
        updateDispenseAllocationSummary();
        return;
    }

    if (isLegacyDispenseSelected()) {
        allocationInputs.forEach(input => {
            input.value = '0';
        });
        updateDispenseAllocationSummary();
        return;
    }

    let remaining = mode === 'pack'
        ? Math.max(0, Math.round(parseFloat(document.getElementById('dispensePackCount')?.value || '0')) || 0)
        : requestedQuantity;
    allocationInputs.forEach(input => {
        const batchId = parseInt(input.dataset.batchId || '', 10);
        const batch = currentDispenseBatches.find(row => row.id === batchId);
        if (!batch || requestedQuantity <= 0) {
            input.value = '0';
            return;
        }

        let allocation = 0;
        if (mode === 'pack' && selectedPack) {
            const availableFullPacks = batchMatchesSelectedPack(batch, selectedPack)
                ? Math.max(0, Math.floor(Number(batch.current_full_pack_count || 0)))
                : 0;
            allocation = Math.min(availableFullPacks, Math.max(remaining, 0));
            input.value = allocation > 0 ? String(allocation) : '0';
        } else {
            allocation = Math.min(getBatchAvailableDispenseQuantity(batch, mode, selectedPack), Math.max(remaining, 0));
            input.value = allocation > 0 ? String(Number(allocation.toFixed(3))) : '0';
        }
        remaining -= allocation;
    });

    updateDispenseAllocationSummary();
}

function updateDispenseAllocationSummary() {
    const summarySection = document.getElementById('batchAllocationSummary');
    const summaryContent = document.getElementById('batchAllocationSummaryContent');
    const requestedQuantity = getDispenseRequestedQuantity();
    const variantId = parseInt(document.getElementById('dispenseDrugSelect').value || '', 10);
    const unitLabel = getVariantById(variantId)?.unit || 'units';
    const inputs = Array.from(document.querySelectorAll('.dispense-batch-allocation'));
    const mode = getSelectedDispenseMode();
    const selectedPack = getSelectedDispensePack();
    const legacyStockOnly = isLegacyDispenseSelected();
    const totalAvailableQuantity = getTotalAvailableDispenseQuantity(mode, selectedPack);
    const totalAvailablePacks = mode === 'pack' ? getTotalAvailableDispensePackCount(selectedPack) : 0;

    if (!summarySection || !summaryContent || !variantId || (!inputs.length && !legacyStockOnly)) {
        if (summarySection) summarySection.style.display = 'none';
        return;
    }

    const allocated = inputs.reduce((sum, input) => {
        const value = parseFloat(input.value || '0');
        return sum + (Number.isNaN(value) ? 0 : value);
    }, 0);
    const allocatedQuantity = mode === 'pack' && selectedPack
        ? allocated * selectedPack.pack_size_in_base_units
        : allocated;
    const invalidInput = inputs.find(input => {
        const batchId = parseInt(input.dataset.batchId || '', 10);
        const batch = currentDispenseBatches.find(row => row.id === batchId);
        const value = parseFloat(input.value || '0');
        if (!batch || Number.isNaN(value)) {
            return false;
        }
        if (mode === 'pack' && selectedPack) {
            const availableFullPacks = batchMatchesSelectedPack(batch, selectedPack)
                ? Math.max(0, Math.floor(Number(batch.current_full_pack_count || 0)))
                : 0;
            return value - availableFullPacks > 1e-6 || Math.abs(value - Math.round(value)) > 1e-6;
        }

        const maxAllocation = getBatchAvailableDispenseQuantity(batch, mode, selectedPack);
        return value - maxAllocation > 1e-6;
    });

    const difference = requestedQuantity - allocatedQuantity;
    summarySection.style.display = 'block';

    if (requestedQuantity <= 0) {
        summaryContent.innerHTML = legacyStockOnly
            ? `<span style="color: #666;">Enter a dispense quantity. ${formatDisplayNumber(currentDispenseLegacyQuantity)} ${escapeHtml(unitLabel)} of legacy stock is available outside batches.</span>`
            : `<span style="color: #666;">Enter a dispense amount to allocate batches.</span>`;
        return;
    }

    if (legacyStockOnly) {
        if (mode === 'pack') {
            summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">Whole-pack dispensing is unavailable for stock that is not attached to batches.</span>`;
            return;
        }
        if (requestedQuantity - currentDispenseLegacyQuantity > 1e-6) {
            summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">Requested ${formatDisplayNumber(requestedQuantity)} ${escapeHtml(unitLabel)} but only ${formatDisplayNumber(currentDispenseLegacyQuantity)} ${escapeHtml(unitLabel)} of legacy stock is available.</span>`;
            return;
        }
        summaryContent.innerHTML = `<span style="color: #1565c0; font-weight: 600;">Dispensing ${formatDisplayNumber(requestedQuantity)} ${escapeHtml(unitLabel)} from legacy stock outside batches.</span>`;
        return;
    }

    if (mode === 'pack' && selectedPack) {
        const requestedPackCount = parseFloat(document.getElementById('dispensePackCount')?.value || '0');
        if (totalAvailablePacks <= 0) {
            summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">No full ${escapeHtml(selectedPack.pack_unit_name)} packs are available to dispense.</span>`;
            return;
        }
        if (!Number.isNaN(requestedPackCount) && requestedPackCount > totalAvailablePacks) {
            summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">Only ${totalAvailablePacks} full ${escapeHtml(selectedPack.pack_unit_name)} pack${totalAvailablePacks === 1 ? '' : 's'} are available.</span>`;
            return;
        }
    }

    if (requestedQuantity - totalAvailableQuantity > 1e-6) {
        summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">Requested ${formatDisplayNumber(requestedQuantity)} ${escapeHtml(unitLabel)} but only ${formatDisplayNumber(totalAvailableQuantity)} ${escapeHtml(unitLabel)} available.</span>`;
        return;
    }

    if (invalidInput) {
        summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">One or more batch allocations exceed available stock or are not valid full-pack amounts.</span>`;
        return;
    }

    if (Math.abs(difference) <= 1e-6) {
        if (mode === 'pack' && selectedPack) {
            const requestedPackCount = parseFloat(document.getElementById('dispensePackCount')?.value || '0');
            summaryContent.innerHTML = `<span style="color: #1565c0; font-weight: 600;">Allocated ${formatDisplayNumber(allocated)} pack${allocated === 1 ? '' : 's'} of ${formatDisplayNumber(requestedPackCount)} requested (${formatDisplayNumber(allocatedQuantity)} ${escapeHtml(unitLabel)}).</span>`;
        } else {
            summaryContent.innerHTML = `<span style="color: #1565c0; font-weight: 600;">Allocated ${formatDisplayNumber(allocatedQuantity)} ${escapeHtml(unitLabel)} of ${formatDisplayNumber(requestedQuantity)} requested.</span>`;
        }
        return;
    }

    if (difference > 0) {
        if (mode === 'pack' && selectedPack) {
            const differencePacks = difference / selectedPack.pack_size_in_base_units;
            summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">Allocate ${formatDisplayNumber(differencePacks)} more pack${Math.abs(differencePacks - 1) <= 1e-6 ? '' : 's'} to match the requested total.</span>`;
        } else {
            summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">Allocate ${formatDisplayNumber(difference)} more ${escapeHtml(unitLabel)} to match the requested total.</span>`;
        }
        return;
    }

    if (mode === 'pack' && selectedPack) {
        const differencePacks = Math.abs(difference) / selectedPack.pack_size_in_base_units;
        summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">Reduce allocations by ${formatDisplayNumber(differencePacks)} pack${Math.abs(differencePacks - 1) <= 1e-6 ? '' : 's'} to match the requested total.</span>`;
        return;
    }

    summaryContent.innerHTML = `<span style="color: #d32f2f; font-weight: 600;">Reduce allocations by ${formatDisplayNumber(Math.abs(difference))} ${escapeHtml(unitLabel)} to match the requested total.</span>`;
}

// Render drugs list
function renderDrugs() {
    const drugsList = document.getElementById('drugsList');
    let drugsToShow = allDrugs;

    // Apply search filter
    if (searchTerm) {
        drugsToShow = drugsToShow.filter(drug => 
            drug.name.toLowerCase().includes(searchTerm) ||
            (drug.description && drug.description.toLowerCase().includes(searchTerm)) ||
            drug.variants.some(variant => variant.strength.toLowerCase().includes(searchTerm))
        );
    }

    // Apply stock filter
    if (showLowStockOnly) {
        drugsToShow = drugsToShow.filter(drug => 
            drug.variants.some(variant => variant.quantity <= variant.low_stock_threshold)
        );
    }

    // Apply location filter using the pre-computed locations list in the summary
    if (selectedLocationFilter) {
        drugsToShow = drugsToShow.filter(drug =>
            (drug.locations || []).includes(selectedLocationFilter)
        );
    }

    // Sort alphabetically by drug name
    drugsToShow = drugsToShow.sort((a, b) => 
        a.name.toLowerCase().localeCompare(b.name.toLowerCase())
    );

    if (drugsToShow.length === 0) {
        drugsList.innerHTML = '<p class="empty">No drugs found matching your criteria</p>';
        return;
    }

    drugsList.innerHTML = drugsToShow.map(drug => {
        const totalVariants = drug.variants.length;
        const lowStockVariants = drug.variants.filter(v => v.quantity <= v.low_stock_threshold).length;
        const totalQuantity = drug.variants.reduce((sum, v) => sum + v.quantity, 0);
        const isLowStock = lowStockVariants > 0;
        const isExpanded = expandedDrugs.has(drug.id);
        const isReadOnly = currentUser.role === 'readonly';
        const isControlled = drug.is_controlled;
        const drugDetail = loadedDrugDetails.get(drug.id);

        let variantsHtml = '';
        if (isExpanded) {
            if (!drugDetail) {
                variantsHtml = '<div class="variant-item" style="padding: 12px; color: #6b7280; font-style: italic;">Loading variants…</div>';
            } else {
                variantsHtml = drug.variants.map(summaryVariant => {
                    // Use detail variant (has packs); fall back to summary if not found
                    const variant = (drugDetail.variants || []).find(v => v.id === summaryVariant.id) || summaryVariant;
                    const variantIsLowStock = summaryVariant.quantity <= summaryVariant.low_stock_threshold;
                    const variantExpanded = expandedVariants.has(summaryVariant.id);
                    // expiredQuantity is pre-computed in the summary
                    const expiredQuantity = summaryVariant.expired_quantity || 0;
                    const inDateQuantity = Math.max(0, Number(summaryVariant.quantity || 0) - expiredQuantity);
                    const quantityDisplay = expiredQuantity > 0
                        ? `${formatDisplayNumber(inDateQuantity)} ${escapeHtml(summaryVariant.unit)} (${formatDisplayNumber(expiredQuantity)} expired)`
                        : `${formatDisplayNumber(summaryVariant.quantity)} ${escapeHtml(summaryVariant.unit)}`;
                    const batches = loadedVariantBatches.get(summaryVariant.id);
                    const batchesSection = (() => {
                        if (!variantExpanded) return '';
                        if (!batches) return '<div style="padding: 10px; color: #6b7280; font-style: italic;">Loading batches…</div>';
                        return renderVariantInventoryDetails(variant, batches);
                    })();
                    return `
                        <div class="variant-item ${variantIsLowStock ? 'low-stock' : ''}" onclick="toggleVariantExpansion(${summaryVariant.id}, event)">
                            <div class="variant-info">
                                <div class="variant-details">
                                    <div class="variant-name">${escapeHtml(drug.name)} ${escapeHtml(summaryVariant.strength)}</div>
                                    <div class="variant-quantity">${quantityDisplay}</div>
                                </div>
                                <div class="variant-status">
                                    <span class="variant-badge ${variantIsLowStock ? 'badge-low' : 'badge-normal'}">
                                        ${variantIsLowStock ? 'Low Stock' : 'OK'}
                                    </span>
                                    <span style="margin-left: 8px; font-size: 0.85em; color: #475569;">Inventory ${variantExpanded ? '▼' : '▶'}</span>
                                </div>
                            </div>
                            <div class="variant-actions">
                                ${!isReadOnly ? `
                                    <button class="btn btn-success btn-small" onclick="event.stopPropagation(); dispenseVariant(${summaryVariant.id})">💊 Dispense</button>
                                    <button class="btn btn-warning btn-small" onclick="event.stopPropagation(); openEditVariantModal(${summaryVariant.id})">Edit</button>
                                    <button class="btn btn-danger btn-small" onclick="event.stopPropagation(); deleteVariant(${summaryVariant.id})" title="${summaryVariant.has_inventory_history ? 'Variant has history and cannot be deleted' : ''}">Delete</button>
                                ` : ''}
                            </div>
                            ${batchesSection}
                        </div>
                    `;
                }).join('');
            }
        }
        
        return `
            <div class="drug-item ${isLowStock ? 'low-stock' : ''} ${isExpanded ? 'expanded' : ''}" onclick="toggleDrugExpansion(${drug.id})">
                <div class="drug-info">
                    <div class="drug-name">
                        ${escapeHtml(drug.name)}
                        ${isControlled ? '<span style="background: #d32f2f; color: white; padding: 2px 6px; border-radius: 2px; font-size: 0.75em; margin-left: 8px; display: inline-block;">⚠️ CONTROLLED</span>' : ''}
                    </div>
                    <div class="drug-description">${drug.description ? escapeHtml(drug.description) : 'No description'}</div>
                    <div class="drug-quantity">${totalVariants} variant${totalVariants !== 1 ? 's' : ''} (${totalQuantity} total units)</div>
                    <div class="drug-status">
                        <span class="drug-badge ${isLowStock ? 'badge-low' : 'badge-normal'}">
                            ${isLowStock ? `${lowStockVariants} low` : 'All OK'}
                        </span>
                    </div>
                </div>
                <div class="drug-actions">
                    ${!isReadOnly ? `
                        <button class="btn btn-primary btn-small" onclick="event.stopPropagation(); openAddVariantModal(${drug.id})">➕ Add</button>
                    ` : ''}
                    <button class="btn btn-info btn-small" onclick="event.stopPropagation(); showDrugHistory(${drug.id})">📋 History</button>
                    ${!isReadOnly ? `
                        <button class="btn btn-warning btn-small" onclick="event.stopPropagation(); openEditModal(${drug.id})">Edit Drug</button>
                        <button class="btn btn-danger btn-small" onclick="event.stopPropagation(); deleteDrug(${drug.id})" title="${drug.variants.some(v => v.has_inventory_history) ? 'Drug has variants with history and cannot be deleted' : ''}">Delete</button>
                    ` : ''}
                    <span class="expand-icon">${isExpanded ? '▼' : '▶'}</span>
                </div>
            </div>
            <div class="drug-variants ${isExpanded ? 'expanded' : ''}" id="variants-${drug.id}">
                ${variantsHtml}
            </div>
        `;
    }).join('');
}

// Handle add drug form
async function handleAddDrug(e) {
    e.preventDefault();

    const drugData = {
        name: document.getElementById('drugName').value,
        description: document.getElementById('drugDescription').value,
        is_controlled: document.getElementById('drugIsControlled').checked
    };

    try {
        const drugResponse = await apiCall('/drugs', {
            method: 'POST',
            body: JSON.stringify(drugData)
        });

        if (!drugResponse.ok) throw new Error('Failed to add drug');
        const createdDrug = await drugResponse.json();

        document.getElementById('drugForm').reset();
        expandedDrugs.add(createdDrug.id);
        await loadDrugs();
        closeModal(document.getElementById('addModal'));
        openAddVariantModal(createdDrug.id);
        showToast('Drug added successfully. Add the first variant next.', 'success');
    } catch (error) {
        console.error('Error adding drug:', error);
        showToast('Failed to add drug. Check the console for details.', 'error');
    }
}

// Handle dispense drug form
async function handleDispenseDrug(e) {
    e.preventDefault();

    const variantId = parseInt(document.getElementById('dispenseDrugSelect').value);
    let quantity = parseFloat(document.getElementById('dispenseQuantity').value);
    const dispenseMode = getSelectedDispenseMode();
    const dispenseSource = getSelectedDispenseSource();
    const requestedPackIdValue = document.getElementById('dispensePackSelect').value;
    const requestedPackCountValue = document.getElementById('dispensePackCount').value;
    const animalName = document.getElementById('dispenseAnimal').value;
    const vetName = document.getElementById('dispenseVet')?.value.trim() || '';
    const notes = document.getElementById('dispenseNotes').value;
    const printEnabled = document.getElementById('dispensePrintEnabled')?.checked;
    const dosage = document.getElementById('dispenseDosage')?.value.trim() || '';
    const legacyExpiryDate = document.getElementById('dispenseLegacyExpiry')?.value || '';

    const selectedPackId = requestedPackIdValue ? parseInt(requestedPackIdValue, 10) : null;
    const selectedPackCount = requestedPackCountValue ? parseFloat(requestedPackCountValue) : null;
    const variant = getVariantById(variantId);
    const drugForVariant = allDrugs.find(d => (d.variants || []).some(v => v.id === variantId));
    const legacyStockOnly = isLegacyDispenseSelected();
    const selectedPack = variant && selectedPackId
        ? getActivePacksForVariant(variant).find(pack => pack.id === selectedPackId)
        : null;

    if (!['subunit', 'pack'].includes(dispenseMode)) {
        showToast('Please select a valid dispense mode.', 'warning');
        return;
    }

    if (dispenseMode === 'pack') {
        if (legacyStockOnly) {
            showToast('Whole-pack dispensing is unavailable for stock that is not attached to batches.', 'warning');
            return;
        }
        if (!selectedPack) {
            showToast('Please select a pack type for whole-pack dispensing.', 'warning');
            return;
        }
        if (selectedPackCount == null || Number.isNaN(selectedPackCount) || selectedPackCount <= 0) {
            showToast('Please enter a valid pack count greater than zero.', 'warning');
            return;
        }
        if (Math.abs(selectedPackCount - Math.round(selectedPackCount)) > 1e-6) {
            showToast('Whole-pack dispensing requires a whole-number pack count.', 'warning');
            return;
        }

        quantity = selectedPackCount * selectedPack.pack_size_in_base_units;
    }

    const allocationEntries = Array.from(document.querySelectorAll('.dispense-batch-allocation'))
        .map(input => ({
            batch_id: parseInt(input.dataset.batchId || '', 10),
            entered_value: parseFloat(input.value || '0')
        }))
        .filter(entry => !Number.isNaN(entry.batch_id) && !Number.isNaN(entry.entered_value) && entry.entered_value > 0);

    const allocations = allocationEntries
        .map(entry => ({
            batch_id: entry.batch_id,
            quantity: dispenseMode === 'pack' && selectedPack
                ? entry.entered_value * selectedPack.pack_size_in_base_units
                : entry.entered_value
        }));

    const allocatedTotal = allocations.reduce((sum, entry) => sum + entry.quantity, 0);
    const totalAvailableQuantity = getTotalAvailableDispenseQuantity(dispenseMode, selectedPack);
    const totalAvailablePacks = dispenseMode === 'pack' ? getTotalAvailableDispensePackCount(selectedPack) : 0;

    if (!variantId || isNaN(quantity) || quantity <= 0) {
        showToast('Please fill in all required fields (Drug Variant and Quantity > 0)', 'warning');
        return;
    }

    if (quantity - totalAvailableQuantity > 1e-6) {
        if (dispenseMode === 'pack' && selectedPack) {
            showToast(`Only ${totalAvailablePacks} full ${selectedPack.pack_unit_name} pack${totalAvailablePacks === 1 ? '' : 's'} available.`, 'warning');
        } else {
            showToast(`Requested quantity exceeds available stock (${formatDisplayNumber(totalAvailableQuantity)} available).`, 'warning');
        }
        return;
    }

    if (!legacyStockOnly && allocations.length === 0) {
        showToast('Allocate quantity against at least one batch.', 'warning');
        return;
    }

    if (dispenseMode === 'pack' && selectedPack) {
        const invalidPackAllocation = allocationEntries.find(entry => {
            const batch = currentDispenseBatches.find(row => row.id === entry.batch_id);
            const availableFullPacks = batchMatchesSelectedPack(batch, selectedPack)
                ? Math.max(0, Math.floor(Number(batch.current_full_pack_count || 0)))
                : 0;
            return !batch
                || entry.entered_value - availableFullPacks > 1e-6
                || Math.abs(entry.entered_value - Math.round(entry.entered_value)) > 1e-6;
        });

        if (invalidPackAllocation) {
            showToast('Whole-pack allocations must use batches with available full packs and whole-pack multiples only.', 'warning');
            return;
        }
    }

    if (!legacyStockOnly && Math.abs(allocatedTotal - quantity) > 1e-6) {
        showToast('Batch allocations must exactly match the requested dispense quantity.', 'warning');
        return;
    }

    const printExpiryDate = printEnabled
        ? (legacyStockOnly ? legacyExpiryDate : getLatestAllocatedBatchExpiryDate(allocationEntries))
        : null;

    if (printEnabled && (!animalName.trim() || !dosage)) {
        showToast('Animal name/ID and dosage instructions are required to print a label.', 'warning');
        return;
    }

    if (printEnabled && !printExpiryDate) {
        showToast(legacyStockOnly
            ? 'Enter an expiry date to print a label for legacy stock.'
            : 'Unable to determine a batch expiry date for the selected allocation.', 'warning');
        return;
    }

    const dispensingData = {
        drug_variant_id: variantId,
        quantity: quantity,
        dispense_mode: dispenseMode,
        requested_pack_id: dispenseMode === 'pack' ? selectedPackId : null,
        requested_pack_count: dispenseMode === 'pack' ? selectedPackCount : null,
        dispense_source: dispenseSource,
        animal_name: animalName || null,
        prescribing_vet: vetName || null,
        notes: notes || null,
        allocations
    };

    if (drugForVariant && drugForVariant.is_controlled && !vetName) {
        showToast('Prescribing vet name is required for controlled drugs.', 'warning');
        document.getElementById('dispenseVet')?.focus();
        return;
    }

    try {
        const response = await apiCall('/dispense', {
            method: 'POST',
            body: JSON.stringify(dispensingData)
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to dispense drug');
        }

        let successMessage = 'Drug dispensed successfully!';
        let toastType = 'success';

        if (printEnabled) {
            try {
                const { drug } = getDrugContextForVariant(variantId);
                const labelResult = await requestLabelPrint({
                    animalName: animalName.trim(),
                    drugName: drug?.name || 'Unknown drug',
                    variantStrength: variant?.strength || '',
                    quantity,
                    unit: variant?.unit || 'units',
                    dosage,
                    expiryDate: printExpiryDate
                });

                if (!labelResult.success) {
                    successMessage = `Drug dispensed, but label printing failed: ${labelResult.message}`;
                    toastType = 'warning';
                } else {
                    successMessage = 'Drug dispensed and label printed successfully!';
                }
            } catch (printError) {
                console.error('Error printing label after dispensing:', printError);
                successMessage = 'Drug dispensed, but label printing failed: ' + printError.message;
                toastType = 'warning';
            }
        }

        document.getElementById('dispenseForm').reset();
        resetDispensePrintFields();
        closeModal(document.getElementById('dispenseModal'));
        loadedVariantBatches.delete(variantId); // invalidate level-3 batch cache
        await loadDrugs();
        showToast(successMessage, toastType, toastType === 'warning' ? 5000 : undefined);
    } catch (error) {
        console.error('Error dispensing drug:', error);
        showToast('Failed to dispense drug: ' + error.message, 'error');
    }
}

// Open edit modal
function openEditModal(drugId) {
    const drug = allDrugs.find(d => d.id === drugId);
    if (!drug) return;

    document.getElementById('editDrugId').value = drug.id;
    document.getElementById('editDrugName').value = drug.name;
    document.getElementById('editDrugDescription').value = drug.description || '';
    document.getElementById('editDrugIsControlled').checked = drug.is_controlled || false;

    openModal(document.getElementById('editModal'));
}

// Close edit modal
function closeEditModal() {
    closeModal(document.getElementById('editModal'));
    document.getElementById('editForm').reset();
}

// Show variants for a drug
async function toggleDrugExpansion(drugId) {
    if (expandedDrugs.has(drugId)) {
        expandedDrugs.delete(drugId);
        const collapsedDrug = allDrugs.find(drug => drug.id === drugId);
        if (collapsedDrug) {
            (collapsedDrug.variants || []).forEach(variant => expandedVariants.delete(variant.id));
        }
        renderDrugs();
    } else {
        expandedDrugs.add(drugId);
        renderDrugs(); // show loading state immediately
        await ensureDrugDetailLoaded(drugId);
        renderDrugs();
    }
}

async function toggleVariantExpansion(variantId, event) {
    if (event) {
        event.stopPropagation();
    }

    if (expandedVariants.has(variantId)) {
        expandedVariants.delete(variantId);
        renderDrugs();
    } else {
        expandedVariants.add(variantId);
        if (!loadedVariantBatches.has(variantId)) {
            renderDrugs(); // show loading state immediately
            try {
                const response = await apiCall(`/variants/${variantId}/batches`);
                if (response.ok) {
                    loadedVariantBatches.set(variantId, await response.json());
                }
            } catch (error) {
                console.error(`Failed to load batches for variant ${variantId}:`, error);
            }
        }
        renderDrugs();
    }
}

// Open add variant modal
function openAddVariantModal(drugId) {
    const drug = allDrugs.find(d => d.id === drugId);
    if (!drug) return;
    
    currentDrug = drug;
    const form = document.getElementById('variantForm');
    if (form) form.reset();
    document.getElementById('variantDrugId').value = drug.id;
    initializeVariantPackRows();
    openModal(document.getElementById('addVariantModal'));
}

function inferBaseUnitFromStrength(strength) {
    const value = String(strength || '').toLowerCase();
    if (value.includes('/ml') || value.includes('ml')) return 'ml';
    if (value.includes('tablet')) return 'tablets';
    if (value.includes('capsule')) return 'capsules';
    return 'tablets';
}

function getVariantPackRowsContainer() {
    return document.getElementById('variantPackRows');
}

function getEditVariantPackRowsContainer() {
    return document.getElementById('editVariantPackRows');
}

function refreshVariantPackRowLabels() {
    const container = getVariantPackRowsContainer();
    const baseUnit = document.getElementById('variantUnit')?.value || 'units';
    if (!container) return;

    container.querySelectorAll('.variant-pack-row').forEach(row => {
        const packUnit = row.querySelector('.variant-pack-unit')?.value || 'pack';
        const label = row.querySelector('.variant-pack-size-label');
        if (!label) return;
        const titleCasePack = packUnit.charAt(0).toUpperCase() + packUnit.slice(1);
        label.textContent = `${titleCasePack} Size (${baseUnit}) *`;
    });
}

function refreshEditVariantPackRowLabels() {
    const container = getEditVariantPackRowsContainer();
    const baseUnit = document.getElementById('editVariantUnit')?.value || 'units';
    if (!container) return;

    container.querySelectorAll('.edit-variant-pack-row').forEach(row => {
        const packUnit = row.querySelector('.edit-variant-pack-unit')?.value || 'pack';
        const label = row.querySelector('.edit-variant-pack-size-label');
        if (!label) return;
        const titleCasePack = packUnit.charAt(0).toUpperCase() + packUnit.slice(1);
        label.textContent = `${titleCasePack} Size (${baseUnit}) *`;
    });
}

function appendVariantPackRow(prefill = {}) {
    const container = getVariantPackRowsContainer();
    if (!container) return;

    const row = document.createElement('div');
    row.className = 'delivery-line variant-pack-row';

    const selectedPackUnit = prefill.packUnit || 'box';
    const selectedSize = prefill.packSize || '';
    const baseUnit = document.getElementById('variantUnit')?.value || 'units';

    row.innerHTML = `
        <div class="delivery-line-grid" style="grid-template-columns: 1.2fr 1.2fr auto;">
            <div class="form-group">
                <label>Pack Type *</label>
                <select class="variant-pack-unit" required>
                    <option value="bottle" ${selectedPackUnit === 'bottle' ? 'selected' : ''}>Bottle</option>
                    <option value="box" ${selectedPackUnit === 'box' ? 'selected' : ''}>Box</option>
                    <option value="vial" ${selectedPackUnit === 'vial' ? 'selected' : ''}>Vial</option>
                    <option value="packet" ${selectedPackUnit === 'packet' ? 'selected' : ''}>Packet</option>
                </select>
            </div>
            <div class="form-group">
                <label class="variant-pack-size-label">Bottle Size (${baseUnit}) *</label>
                <input type="number" class="variant-pack-size" min="1" step="1" value="${selectedSize}" required>
            </div>
            <button type="button" class="btn btn-danger btn-small variant-pack-remove-btn">Remove</button>
        </div>
    `;

    const removeBtn = row.querySelector('.variant-pack-remove-btn');
    const unitSelect = row.querySelector('.variant-pack-unit');
    if (removeBtn) {
        removeBtn.addEventListener('click', () => {
            if (container.querySelectorAll('.variant-pack-row').length <= 1) {
                showToast('At least one pack size is required', 'warning');
                return;
            }
            row.remove();
        });
    }

    if (unitSelect) {
        unitSelect.addEventListener('change', refreshVariantPackRowLabels);
    }

    container.appendChild(row);
    refreshVariantPackRowLabels();
}

function initializeVariantPackRows() {
    const container = getVariantPackRowsContainer();
    if (!container) return;
    container.innerHTML = '';

    const strengthValue = document.getElementById('variantStrength')?.value || '';
    const inferredBaseUnit = inferBaseUnitFromStrength(strengthValue);
    const variantUnitSelect = document.getElementById('variantUnit');
    if (variantUnitSelect) {
        variantUnitSelect.value = inferredBaseUnit;
    }

    appendVariantPackRow({ packUnit: 'box' });
}

function appendEditVariantPackRow(prefill = {}) {
    const container = getEditVariantPackRowsContainer();
    if (!container) return;

    const row = document.createElement('div');
    row.className = 'delivery-line edit-variant-pack-row';

    const selectedPackUnit = prefill.packUnit || 'bottle';
    const selectedSize = prefill.packSize || '';
    const baseUnit = document.getElementById('editVariantUnit')?.value || 'units';

    row.innerHTML = `
        <div class="delivery-line-grid" style="grid-template-columns: 1.2fr 1.2fr auto;">
            <div class="form-group">
                <label>Pack Type *</label>
                <select class="edit-variant-pack-unit">
                    <option value="bottle" ${selectedPackUnit === 'bottle' ? 'selected' : ''}>Bottle</option>
                    <option value="box" ${selectedPackUnit === 'box' ? 'selected' : ''}>Box</option>
                    <option value="vial" ${selectedPackUnit === 'vial' ? 'selected' : ''}>Vial</option>
                    <option value="packet" ${selectedPackUnit === 'packet' ? 'selected' : ''}>Packet</option>
                </select>
            </div>
            <div class="form-group">
                <label class="edit-variant-pack-size-label">Bottle Size (${baseUnit}) *</label>
                <input type="number" class="edit-variant-pack-size" min="0.0001" step="0.0001" value="${selectedSize}">
            </div>
            <button type="button" class="btn btn-danger btn-small edit-variant-pack-remove-btn">Remove</button>
        </div>
    `;

    const removeBtn = row.querySelector('.edit-variant-pack-remove-btn');
    const unitSelect = row.querySelector('.edit-variant-pack-unit');
    if (removeBtn) {
        removeBtn.addEventListener('click', () => {
            row.remove();
        });
    }

    if (unitSelect) {
        unitSelect.addEventListener('change', refreshEditVariantPackRowLabels);
    }

    container.appendChild(row);
    refreshEditVariantPackRowLabels();
}

function initializeEditVariantPackRows() {
    const container = getEditVariantPackRowsContainer();
    if (!container) return;
    container.innerHTML = '';
    appendEditVariantPackRow({ packUnit: 'bottle' });
}

function setEditVariantFieldLockState(isLocked) {
    const strengthInput = document.getElementById('editVariantStrength');
    const quantityInput = document.getElementById('editVariantQuantity');
    const unitSelect = document.getElementById('editVariantUnit');
    const lockNotice = document.getElementById('editVariantLockNotice');

    if (strengthInput) strengthInput.disabled = isLocked;
    if (quantityInput) quantityInput.disabled = isLocked;
    if (unitSelect) unitSelect.disabled = isLocked;
    if (lockNotice) lockNotice.style.display = isLocked ? 'block' : 'none';
}

// Handle add variant form
async function handleAddVariant(e) {
    e.preventDefault();

    const drugId = parseInt(document.getElementById('variantDrugId').value);
    const baseUnit = document.getElementById('variantUnit').value;
    const rows = Array.from(document.querySelectorAll('#variantPackRows .variant-pack-row'));

    if (rows.length === 0) {
        showToast('Please add at least one pack size', 'warning');
        return;
    }

    const packPayloads = [];
    for (let i = 0; i < rows.length; i += 1) {
        const row = rows[i];
        const packUnit = row.querySelector('.variant-pack-unit')?.value;
        const packSize = parseFloat(row.querySelector('.variant-pack-size')?.value || '');

        if (!packUnit || Number.isNaN(packSize) || packSize <= 0) {
            showToast(`Pack row ${i + 1} is incomplete`, 'warning');
            return;
        }

        const normalizedPackUnit = packUnit.trim().toLowerCase();
        const titleCasePack = normalizedPackUnit.charAt(0).toUpperCase() + normalizedPackUnit.slice(1);
        packPayloads.push({
            label: `${titleCasePack} ${packSize} ${baseUnit}`,
            pack_unit_name: normalizedPackUnit,
            pack_size_in_base_units: packSize,
            is_active: true
        });
    }

    const variantData = {
        strength: document.getElementById('variantStrength').value,
        quantity: 0,
        unit: baseUnit,
        base_unit: baseUnit,
        low_stock_threshold: parseFloat(document.getElementById('variantThreshold').value)
    };

    try {
        const response = await apiCall(`/drugs/${drugId}/variants`, {
            method: 'POST',
            body: JSON.stringify(variantData)
        });

        if (!response.ok) throw new Error('Failed to add variant');

        const createdVariant = await response.json();

        for (const packPayload of packPayloads) {
            const packResponse = await apiCall(`/variants/${createdVariant.id}/packs`, {
                method: 'POST',
                body: JSON.stringify(packPayload)
            });

            if (!packResponse.ok) {
                const packError = await packResponse.json();
                throw new Error(packError.detail || 'Variant created but pack size creation failed');
            }
        }

        // Archive the auto-created default 1:1 pack when custom pack sizes are configured.
        const packsResponse = await apiCall(`/variants/${createdVariant.id}/packs`);
        if (packsResponse.ok) {
            const packs = await packsResponse.json();
            const defaultPack = packs.find(
                p => p.is_active && Number(p.pack_size_in_base_units) === 1 && (p.pack_unit_name || '').toLowerCase() === baseUnit.toLowerCase()
            );
            if (defaultPack && packs.filter(p => p.is_active).length > 1) {
                await apiCall(`/variant-packs/${defaultPack.id}`, {
                    method: 'PUT',
                    body: JSON.stringify({ is_active: false })
                });
            }
        }

        document.getElementById('variantForm').reset();
        closeModal(document.getElementById('addVariantModal'));
        loadedDrugDetails.delete(drugId); // invalidate level-2 cache for this drug
        await loadDrugs();
        if (document.getElementById('receiveDeliveryModal')?.classList.contains('show')) {
            refreshDeliveryVariantSelects();
        }
        renderDrugs();
        showToast('Variant added successfully!', 'success');
    } catch (error) {
        console.error('Error adding variant:', error);
        showToast('Failed to add variant. Check the console for details.', 'error');
    }
}

// Open edit variant modal
function openEditVariantModal(variantId) {
    // Find the variant from all drugs
    let variant = null;
    for (const drug of allDrugs) {
        variant = drug.variants.find(v => v.id === variantId);
        if (variant) break;
    }
    
    if (!variant) return;

    document.getElementById('editVariantId').value = variant.id;
    document.getElementById('editVariantStrength').value = variant.strength;
    document.getElementById('editVariantQuantity').value = variant.quantity;
    document.getElementById('editVariantUnit').value = variant.unit;
    document.getElementById('editVariantThreshold').value = variant.low_stock_threshold;

    const hasInventoryContext = Boolean(variant.has_inventory_history);
    setEditVariantFieldLockState(hasInventoryContext);
    initializeEditVariantPackRows();

    openModal(document.getElementById('editVariantModal'));
}

// Handle edit variant form
async function handleEditVariant(e) {
    e.preventDefault();

    const variantId = parseInt(document.getElementById('editVariantId').value);
    const strengthInput = document.getElementById('editVariantStrength');
    const quantityInput = document.getElementById('editVariantQuantity');
    const unitSelect = document.getElementById('editVariantUnit');
    const baseUnit = unitSelect.value;
    const variantData = {
        low_stock_threshold: parseFloat(document.getElementById('editVariantThreshold').value)
    };

    if (!strengthInput.disabled && !quantityInput.disabled && !unitSelect.disabled) {
        const quantityValue = parseFloat(quantityInput.value);
        if (Number.isNaN(quantityValue) || quantityValue < 0) {
            showToast('Please enter a valid quantity (0 or greater)', 'warning');
            return;
        }

        variantData.strength = strengthInput.value;
        variantData.quantity = quantityValue;
        variantData.unit = baseUnit;
        variantData.base_unit = baseUnit;
    }

    const packRows = Array.from(document.querySelectorAll('#editVariantPackRows .edit-variant-pack-row'));
    const newPackPayloads = [];
    for (let i = 0; i < packRows.length; i += 1) {
        const row = packRows[i];
        const packUnitRaw = row.querySelector('.edit-variant-pack-unit')?.value || '';
        const packSizeRaw = row.querySelector('.edit-variant-pack-size')?.value || '';

        if (!packUnitRaw && !packSizeRaw) {
            continue;
        }

        const packSize = parseFloat(packSizeRaw);
        if (!packUnitRaw || Number.isNaN(packSize) || packSize <= 0) {
            showToast(`Pack row ${i + 1} is incomplete`, 'warning');
            return;
        }

        const normalizedPackUnit = packUnitRaw.trim().toLowerCase();
        const titleCasePack = normalizedPackUnit.charAt(0).toUpperCase() + normalizedPackUnit.slice(1);
        newPackPayloads.push({
            label: `${titleCasePack} ${packSize} ${baseUnit}`,
            pack_unit_name: normalizedPackUnit,
            pack_size_in_base_units: packSize,
            is_active: true
        });
    }

    try {
        const response = await apiCall(`/variants/${variantId}`, {
            method: 'PUT',
            body: JSON.stringify(variantData)
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to update variant');
        }

        for (const packPayload of newPackPayloads) {
            const packResponse = await apiCall(`/variants/${variantId}/packs`, {
                method: 'POST',
                body: JSON.stringify(packPayload)
            });

            if (!packResponse.ok) {
                const packError = await packResponse.json();
                throw new Error(packError.detail || 'Variant updated but failed to add one or more pack sizes');
            }
        }

        closeModal(document.getElementById('editVariantModal'));
        const variantDrugId = allDrugs.find(d => (d.variants || []).some(v => v.id === variantId))?.id;
        if (variantDrugId) loadedDrugDetails.delete(variantDrugId); // invalidate level-2 cache
        await loadDrugs();
        renderDrugs();
        const message = newPackPayloads.length > 0
            ? `Variant updated and ${newPackPayloads.length} pack size${newPackPayloads.length === 1 ? '' : 's'} added`
            : 'Variant updated successfully!';
        showToast(message, 'success');
    } catch (error) {
        console.error('Error updating variant:', error);
        showToast('Failed to update variant: ' + error.message, 'error');
    }
}
// Dispense from variant
function dispenseVariant(variantId) {
    // Update the dropdown display with all variants
    updateDispenseDrugSelect();
    
    // Pre-select the variant in the dispense modal
    const drugSelect = document.getElementById('dispenseDrugSelect');
    drugSelect.value = variantId;
    
    // Update batch info for selected variant
    updateBatchInfo();
    
    // Open dispense modal
    openModal(document.getElementById('dispenseModal'));
}

// Handle print notes form submission
async function handlePrintNotes(e) {
    e.preventDefault();

    const animalName = document.getElementById('notesAnimalName').value.trim();
    const notes = document.getElementById('notesContent').value.trim();

    if (!animalName || !notes) {
        showToast('Please fill in all required fields', 'warning');
        return;
    }

    try {
        // Send notes to print endpoint
        const notesData = {
            variables: {
                animal_name: animalName,
                notes: notes
            }
        };

        const response = await apiCall('/notes/print', {
            method: 'POST',
            body: JSON.stringify(notesData)
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Notes printing request failed');
        }

        const result = await response.json();
        console.log('Notes print result:', result);
        
        if (!result.success) {
            // Printing failed
            const isError = result.message && (
                result.message.includes('not found') || 
                result.message.includes('error') ||
                result.message.includes('failed')
            );
            const toastType = isError ? 'error' : 'warning';
            showToast(result.message, toastType, 5000);
            return;
        }

        // Printing succeeded
        showToast('Notes printed successfully!', 'success');

        document.getElementById('printNotesForm').reset();
        closeModal(document.getElementById('printNotesModal'));
    } catch (error) {
        console.error('Error printing notes:', error);
        showToast('Failed to print notes: ' + error.message, 'error');
    }
}

// Delete variant
async function deleteVariant(variantId) {
    const variant = getVariantById(variantId);
    if (variant && variant.has_inventory_history) {
        showToast('Cannot delete variant with batch or dispensing history', 'warning');
        return;
    }

    if (!confirm('Are you sure you want to delete this variant?')) return;

    try {
        const response = await apiCall(`/variants/${variantId}`, {
            method: 'DELETE'
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to delete variant');
        }

        await loadDrugs();
        renderDrugs();
        showToast('Variant deleted successfully!', 'success');
    } catch (error) {
        console.error('Error deleting variant:', error);
        showToast('Failed to delete variant: ' + error.message, 'error');
    }
}

// Show dispensing history for a drug
async function showDrugHistory(drugId) {
    const drug = allDrugs.find(d => d.id === drugId);
    if (!drug) return;

    const historyModal = document.getElementById('historyModal');
    const historyContent = document.getElementById('historyContent');
    document.getElementById('historyDrugName').textContent = drug.name;
    
    historyContent.innerHTML = '<p class="loading">Loading history...</p>';
    openModal(historyModal);
    
    try {
        const response = await apiCall(`/dispense/history`);
        if (!response.ok) throw new Error('Failed to fetch history');
        
        const allHistory = await response.json();
        
        // Filter history for this drug's variants
        const variantIds = drug.variants.map(v => v.id);
        const drugHistory = allHistory.filter(item => variantIds.includes(item.drug_variant_id));
        
        if (drugHistory.length === 0) {
            historyContent.innerHTML = '<p class="empty">No dispensing history for this drug.</p>';
            return;
        }
        
        // Sort by dispensed_at descending (most recent first)
        drugHistory.sort((a, b) => new Date(b.dispensed_at) - new Date(a.dispensed_at));
        
        const historyHtml = drugHistory.map(item => {
            const variant = drug.variants.find(v => v.id === item.drug_variant_id);
            const date = new Date(item.dispensed_at).toLocaleDateString();
            const time = new Date(item.dispensed_at).toLocaleTimeString();
            
            return `
                <div class="history-item">
                    <div class="history-header">
                        <div class="history-variant">${drug.name} ${variant.strength}</div>
                        <div class="history-datetime">${date} ${time}</div>
                    </div>
                    <div class="history-details">
                        <div class="history-row">
                            <span class="history-label">Quantity:</span>
                            <span class="history-value">${item.quantity} ${variant.unit}</span>
                        </div>
                        <div class="history-row">
                            <span class="history-label">Animal:</span>
                            <span class="history-value">${escapeHtml(item.animal_name)}</span>
                        </div>
                        <div class="history-row">
                            <span class="history-label">User:</span>
                            <span class="history-value">${escapeHtml(item.user_name)}</span>
                        </div>
                        ${item.prescribing_vet ? `
                        <div class="history-row">
                            <span class="history-label">Prescribing Vet:</span>
                            <span class="history-value">${escapeHtml(item.prescribing_vet)}</span>
                        </div>
                        ` : ''}
                        ${item.notes ? `
                        <div class="history-row">
                            <span class="history-label">Notes:</span>
                            <span class="history-value">${escapeHtml(item.notes)}</span>
                        </div>
                        ` : ''}
                    </div>
                </div>
            `;
        }).join('');
        
        historyContent.innerHTML = historyHtml;
    } catch (error) {
        console.error('Error fetching history:', error);
        historyContent.innerHTML = '<p class="error">Failed to load history. Check the console for details.</p>';
    }
}

// Handle edit drug form
async function handleEditDrug(e) {
    e.preventDefault();

    const drugId = parseInt(document.getElementById('editDrugId').value);
    const drugData = {
        name: document.getElementById('editDrugName').value,
        description: document.getElementById('editDrugDescription').value,
        is_controlled: document.getElementById('editDrugIsControlled').checked
    };

    try {
        const response = await apiCall(`/drugs/${drugId}`, {
            method: 'PUT',
            body: JSON.stringify(drugData)
        });

        if (!response.ok) throw new Error('Failed to update drug');

        closeEditModal();
        loadedDrugDetails.delete(drugId); // invalidate level-2 cache
        await loadDrugs();
        showToast('Drug updated successfully!', 'success');
    } catch (error) {
        console.error('Error updating drug:', error);
        showToast('Failed to update drug. Check the console for details.', 'error');
    }
}

// Delete drug
async function deleteDrug(drugId) {
    const drug = allDrugs.find(d => d.id === drugId);
    if (drug && drug.variants.some(v => v.has_inventory_history)) {
        showToast('Cannot delete drug with variants that have batch or dispensing history', 'warning');
        return;
    }

    if (!confirm('Are you sure you want to delete this drug?')) return;

    try {
        const response = await apiCall(`/drugs/${drugId}`, {
            method: 'DELETE'
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to delete drug');
        }

        loadedDrugDetails.delete(drugId); // invalidate level-2 cache
        loadedVariantBatches.clear(); // variants of this drug are gone
        await loadDrugs();
        showToast('Drug deleted successfully!', 'success');
    } catch (error) {
        console.error('Error deleting drug:', error);
        showToast('Failed to delete drug: ' + error.message, 'error');
    }
}

// Password Management
function openChangePasswordModal() {
    const modal = document.getElementById('changePasswordModal');
    document.getElementById('changePasswordForm').reset();
    
    // Close dropdown
    const dropdown = document.getElementById('userDropdown');
    if (dropdown) dropdown.style.display = 'none';
    
    openModal(modal);
}

async function handleChangePassword(e) {
    e.preventDefault();
    
    const currentPassword = document.getElementById('currentPassword').value;
    const newPassword = document.getElementById('newPassword').value;
    const confirmPassword = document.getElementById('confirmNewPassword').value;
    
    if (newPassword !== confirmPassword) {
        showToast('New passwords do not match!', 'warning');
        return;
    }
    
    if (newPassword.length < 1) {
        showToast('New password cannot be empty!', 'warning');
        return;
    }
    
    try {
        const response = await apiCall('/auth/change-password', {
            method: 'POST',
            body: JSON.stringify({
                current_password: currentPassword,
                new_password: newPassword
            })
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to change password');
        }

        showToast('Password changed successfully!', 'success');
        closeModal(document.getElementById('changePasswordModal'));
    } catch (error) {
        console.error('Error changing password:', error);
        showToast('Failed to change password: ' + error.message, 'error');
    }
}

async function openAdminChangePasswordModal(userId, username) {
    const modal = document.getElementById('adminChangePasswordModal');
    document.getElementById('adminChangePasswordForm').reset();
    document.getElementById('adminChangePasswordUserId').value = userId;
    document.getElementById('adminChangePasswordUsername').value = username;
    openModal(modal);
}

async function handleAdminChangePassword(e) {
    e.preventDefault();
    
    const userId = document.getElementById('adminChangePasswordUserId').value;
    const newPassword = document.getElementById('adminChangePasswordNewPassword').value;
    const confirmPassword = document.getElementById('adminChangePasswordConfirm').value;
    
    if (newPassword !== confirmPassword) {
        showToast('Passwords do not match!', 'warning');
        return;
    }
    
    if (newPassword.length < 1) {
        showToast('Password cannot be empty!', 'warning');
        return;
    }
    
    try {
        const response = await apiCall(`/users/${userId}/change-password`, {
            method: 'POST',
            body: JSON.stringify({
                new_password: newPassword
            })
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to change password');
        }

        showToast('Password changed successfully!', 'success');
        closeModal(document.getElementById('adminChangePasswordModal'));
        openUserManagement();
    } catch (error) {
        console.error('Error changing password:', error);
        showToast('Failed to change password: ' + error.message, 'error');
    }
}

// Update filter button states
function updateFilterButtons() {
    document.getElementById('showAllBtn').classList.toggle('active', !showLowStockOnly);
    document.getElementById('showLowStockBtn').classList.toggle('active', showLowStockOnly);
}

// Escape HTML to prevent XSS
function escapeHtml(text) {
    const div = document.createElement('div');
    div.textContent = text;
    return div.innerHTML;
}

function toTitleCase(str) {
    return str.replace(/\S+/g, word => word.charAt(0).toUpperCase() + word.slice(1));
}

async function openReportsPage() {
    const dropdown = document.getElementById('userDropdown');
    if (dropdown) dropdown.style.display = 'none';

    window.location.href = 'reports.html';
}

// User Management
async function openUserManagement() {
    const modal = document.getElementById('userManagementModal');
    document.getElementById('newUsername').value = '';
    document.getElementById('newUserPassword').value = '';
    document.getElementById('newUserRole').value = '';
    
    const usersList = document.getElementById('usersList');
    usersList.innerHTML = '<h3>Users</h3><p class="loading">Loading users...</p>';
    
    try {
        const response = await apiCall('/users');
        if (!response.ok) throw new Error('Failed to load users');

        const users = await response.json();
        
        const usersHtml = `
            <h3>Users</h3>
            <div class="users-table">
                ${users.map(user => {
                    const roleLabel = user.role.charAt(0).toUpperCase() + user.role.slice(1);
                    const roleBadge = user.role === 'admin' ? '👑 Admin' : 
                                     user.role === 'readonly' ? '👁️ Read-Only' : '👤 Regular';
                    return `
                        <div class="user-item">
                            <span>${user.username}</span>
                            <span class="admin-badge">${roleBadge}</span>
                            <button class="btn btn-secondary btn-small" onclick="openAdminChangePasswordModal(${user.id}, '${escapeHtml(user.username)}')">🔑 Password</button>
                            ${user.id !== currentUser.id ? `
                                <button class="btn btn-danger btn-small" onclick="deleteUser(${user.id})">Delete</button>
                            ` : ''}
                        </div>
                    `;
                }).join('')}
            </div>
        `;
        
        usersList.innerHTML = usersHtml;
    } catch (error) {
        console.error('Error loading users:', error);
        usersList.innerHTML = '<h3>Users</h3><p class="empty">Error loading users</p>';
    }
    
    const createUserForm = document.getElementById('createUserForm');
    if (createUserForm) {
        createUserForm.onsubmit = createUser;
    }
    
    openModal(modal);
}

// Create user
async function createUser(e) {
    e.preventDefault();
    
    const username = document.getElementById('newUsername').value;
    const password = document.getElementById('newUserPassword').value;
    const role = document.getElementById('newUserRole').value;
    
    if (!role) {
        showToast('Please select a role', 'warning');
        return;
    }
    
    try {
        const response = await apiCall('/users', {
            method: 'POST',
            body: JSON.stringify({ username, password, role })
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to create user');
        }

        document.getElementById('newUsername').value = '';
        document.getElementById('newUserPassword').value = '';
        document.getElementById('newUserRole').value = '';
        showToast('User created successfully!', 'success');
        openUserManagement();
    } catch (error) {
        console.error('Error creating user:', error);
        showToast('Failed to create user: ' + error.message, 'error');
    }
}

// Delete user
async function deleteUser(userId) {
    if (!confirm('Are you sure you want to delete this user?')) return;

    try {
        const response = await apiCall(`/users/${userId}`, { method: 'DELETE' });

        if (!response.ok) throw new Error('Failed to delete user');

        showToast('User deleted successfully!', 'success');
        openUserManagement();
    } catch (error) {
        console.error('Error deleting user:', error);
        showToast('Failed to delete user: ' + error.message, 'error');
    }
}

// Location Management
async function openLocationManagement() {
    const modal = document.getElementById('locationManagementModal');
    document.getElementById('newLocationName').value = '';
    
    const locationsList = document.getElementById('locationsList');
    locationsList.innerHTML = '<h3>Active Locations</h3><p class="loading">Loading locations...</p>';
    
    try {
        const response = await apiCall('/locations');
        if (!response.ok) throw new Error('Failed to load locations');

        const locations = await response.json();
        
        const activeLocations = locations.filter(loc => loc.is_active);
        const inactiveLocations = locations.filter(loc => !loc.is_active);
        
        let locationsHtml = '<h3>Active Locations</h3>';
        if (activeLocations.length === 0) {
            locationsHtml += '<p class="empty">No active locations</p>';
        } else {
            locationsHtml += `<div class="locations-table">
                ${activeLocations.map(location => `
                    <div class="location-item">
                        <div style="flex: 1;">
                            <strong>${location.name}</strong>
                            <div style="font-size: 0.85em; color: #666;">Created: ${new Date(location.created_at).toLocaleDateString()}</div>
                        </div>
                        <button class="btn btn-danger btn-small" onclick="archiveLocation(${location.id}, '${location.name.replace(/'/g, "\\'")}')">Archive</button>
                    </div>
                `).join('')}
            </div>`;
        }
        
        if (inactiveLocations.length > 0) {
            locationsHtml += `
                <h3 style="margin-top: 20px;">Archived Locations</h3>
                <div class="locations-table">
                    ${inactiveLocations.map(location => `
                        <div class="location-item" style="opacity: 0.6;">
                            <div style="flex: 1;">
                                <strong>${location.name}</strong> <span style="color: #999;">(archived)</span>
                            </div>
                            <button class="btn btn-secondary btn-small" onclick="restoreLocation(${location.id}, '${location.name.replace(/'/g, "\\'")}')">Restore</button>
                        </div>
                    `).join('')}
                </div>
            `;
        }
        
        locationsList.innerHTML = locationsHtml;
    } catch (error) {
        console.error('Error loading locations:', error);
        locationsList.innerHTML = '<h3>Active Locations</h3><p class="empty">Error loading locations</p>';
    }
    
    openModal(modal);
}

// Create location
async function createLocation(e) {
    e.preventDefault();
    
    const name = document.getElementById('newLocationName').value.trim();
    
    if (!name) {
        showToast('Please enter a location name', 'warning');
        return;
    }
    
    try {
        const response = await apiCall('/locations', {
            method: 'POST',
            body: JSON.stringify({ name })
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to create location');
        }

        document.getElementById('newLocationName').value = '';
        showToast('Location created successfully!', 'success');
        openLocationManagement();
    } catch (error) {
        console.error('Error creating location:', error);
        showToast('Failed to create location: ' + error.message, 'error');
    }
}

// Archive location
async function archiveLocation(locationId, locationName) {
    if (!confirm(`Archive location "${locationName}"?\n\nYou can restore it later if needed.`)) return;

    try {
        const response = await apiCall(`/locations/${locationId}`, {
            method: 'PUT',
            body: JSON.stringify({ is_active: false })
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to archive location');
        }

        showToast('Location archived successfully!', 'success');
        openLocationManagement();
    } catch (error) {
        console.error('Error archiving location:', error);
        showToast('Failed to archive location: ' + error.message, 'error');
    }
}

// Restore location
async function restoreLocation(locationId, locationName) {
    if (!confirm(`Restore location "${locationName}"?`)) return;

    try {
        const response = await apiCall(`/locations/${locationId}`, {
            method: 'PUT',
            body: JSON.stringify({ is_active: true })
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to restore location');
        }

        showToast('Location restored successfully!', 'success');
        openLocationManagement();
    } catch (error) {
        console.error('Error restoring location:', error);
        showToast('Failed to restore location: ' + error.message, 'error');
    }
}

// Batch Management
async function openBatchReceiveModal(variantId) {
    const batchReceiveModal = document.getElementById('batchReceiveModal');
    document.getElementById('batchReceiveForm').reset();
    document.getElementById('batchVariantId').value = variantId;
    
    // Initialize locations
    await initializeBatchLocations();
    
    openModal(batchReceiveModal);
}

async function initializeBatchLocations() {
    const locationSelect = document.getElementById('batchLocation');
    
    try {
        const response = await apiCall('/locations');
        if (!response.ok) throw new Error('Failed to load locations');
        
        const locations = await response.json();
        
        locationSelect.innerHTML = '<option value="">-- Select location --</option>';
        locations.forEach(location => {
            if (location.is_active) {
                const option = document.createElement('option');
                option.value = location.id;
                option.textContent = location.name;
                locationSelect.appendChild(option);
            }
        });
    } catch (error) {
        console.error('Error loading locations:', error);
        showToast('Failed to load storage locations', 'error');
    }
}

async function handleBatchReceive(e) {
    e.preventDefault();
    
    const variantId = parseInt(document.getElementById('batchVariantId').value);
    const batchNumber = document.getElementById('batchNumber').value.trim();
    const quantity = parseFloat(document.getElementById('batchQuantity').value);
    const expiryDate = document.getElementById('batchExpiryDate').value;
    const locationId = parseInt(document.getElementById('batchLocation').value);
    const notes = document.getElementById('batchNotes').value.trim();
    
    if (!batchNumber || isNaN(quantity) || quantity <= 0 || !expiryDate || !locationId) {
        showToast('Please fill in all required fields', 'warning');
        return;
    }
    
    const batchData = {
        batch_number: batchNumber,
        quantity: quantity,
        expiry_date: expiryDate,
        location_id: locationId,
        notes: notes || null
    };
    
    try {
        const response = await apiCall(`/variants/${variantId}/batches`, {
            method: 'POST',
            body: JSON.stringify(batchData)
        });
        
        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to receive batch');
        }
        
        document.getElementById('batchReceiveForm').reset();
        closeModal(document.getElementById('batchReceiveModal'));
        loadedVariantBatches.delete(variantId); // invalidate level-3 cache
        await loadDrugs();
        showToast('Batch received successfully!', 'success');
    } catch (error) {
        console.error('Error receiving batch:', error);
        showToast('Failed to receive batch: ' + error.message, 'error');
    }
}

function getActiveDeliveryDrug() {
    return allDrugs.find(d => d.id === deliveryDrugId);
}

function getVariantById(variantId) {
    // Prefer loaded drug details (have packs)
    for (const detail of loadedDrugDetails.values()) {
        const found = (detail.variants || []).find(v => v.id === variantId);
        if (found) return found;
    }
    // Fall back to summary variant (no packs)
    for (const drug of allDrugs) {
        const found = (drug.variants || []).find(v => v.id === variantId);
        if (found) return found;
    }
    return null;
}

async function ensureDrugDetailLoaded(drugId) {
    if (!drugId || loadedDrugDetails.has(drugId)) return;
    try {
        const response = await apiCall(`/drugs/${drugId}`);
        if (response.ok) {
            loadedDrugDetails.set(drugId, await response.json());
        }
    } catch (error) {
        console.error(`Failed to load drug detail for drug ${drugId}:`, error);
    }
}

function buildDeliveryVariantOptions(drug, selectedVariantId = '') {
    if (!drug || !drug.variants || drug.variants.length === 0) {
        return '<option value="">-- No variants available --</option>';
    }

    return [`<option value="">-- Select variant --</option>`, ...drug.variants.map(v => {
        const selected = String(v.id) === String(selectedVariantId) ? ' selected' : '';
        return `<option value="${v.id}"${selected}>${escapeHtml(v.strength)} (${escapeHtml(v.unit)})</option>`;
    })].join('');
}

function getActivePacksForVariant(variant) {
    if (!variant || !Array.isArray(variant.packs)) return [];
    return variant.packs.filter(pack => pack.is_active);
}

function buildDeliveryPackOptions(variant, selectedPackId = '') {
    const packs = getActivePacksForVariant(variant);
    if (packs.length === 0) {
        return '<option value="">-- No active packs --</option>';
    }

    return [`<option value="">-- Select pack --</option>`, ...packs.map(pack => {
        const selected = String(pack.id) === String(selectedPackId) ? ' selected' : '';
        const label = `${packLabel(pack)} (${pack.pack_size_in_base_units} ${variant.unit})`;
        return `<option value="${pack.id}"${selected}>${escapeHtml(label)}</option>`;
    })].join('');
}

function buildDeliveryLocationOptions(selectedLocationId = '') {
    const fallbackLocationId = selectedLocationId || (deliveryLocations.length > 0 ? String(deliveryLocations[0].id) : '');
    return [`<option value="">-- Select location --</option>`, ...deliveryLocations.map(location => {
        const selected = String(location.id) === String(fallbackLocationId) ? ' selected' : '';
        return `<option value="${location.id}"${selected}>${escapeHtml(location.name)}</option>`;
    })].join('');
}

function updateDeliveryLineQuantityDisplay(line) {
    const variantId = parseInt(line.querySelector('.delivery-variant-select')?.value || '', 10);
    const packSelect = line.querySelector('.delivery-pack-select');

    const variant = getVariantById(variantId);
    if (!variant || !packSelect) {
        return;
    }

    const currentPackId = packSelect.value;
    packSelect.innerHTML = buildDeliveryPackOptions(variant, currentPackId);
}

function wireDeliveryLineEvents(line) {
    const drugSelect = line.querySelector('.delivery-drug-select');
    const variantSelect = line.querySelector('.delivery-variant-select');
    const packSelect = line.querySelector('.delivery-pack-select');
    const packCountInput = line.querySelector('.delivery-pack-count');

    if (drugSelect && variantSelect) {
        drugSelect.addEventListener('change', async () => {
            const drugId = parseInt(drugSelect.value || '', 10);
            await ensureDrugDetailLoaded(drugId);
            const drug = allDrugs.find(d => d.id === drugId) || null;
            variantSelect.innerHTML = buildDeliveryVariantOptions(drug, '');
            if (packSelect) packSelect.innerHTML = buildDeliveryPackOptions(null, '');
            if (packCountInput) packCountInput.value = '';
            updateDeliveryLineQuantityDisplay(line);
        });
    }

    if (variantSelect && packSelect) {
        variantSelect.addEventListener('change', () => {
            const variantId = parseInt(variantSelect.value || '', 10);
            const variant = getVariantById(variantId);
            const activePacks = getActivePacksForVariant(variant);
            const nextPackId = activePacks.length === 1 ? activePacks[0].id : '';
            packSelect.innerHTML = buildDeliveryPackOptions(variant, nextPackId);
            if (packCountInput) packCountInput.value = '';
            updateDeliveryLineQuantityDisplay(line);
        });
    }

    if (packSelect) {
        packSelect.addEventListener('change', () => {
            updateDeliveryLineQuantityDisplay(line);
        });
    }

    if (packCountInput) {
        // Prevent accidental value changes when users scroll while focused.
        packCountInput.addEventListener('wheel', (event) => {
            event.preventDefault();
        }, { passive: false });

        packCountInput.addEventListener('input', () => {
            updateDeliveryLineQuantityDisplay(line);
        });
    }
}

// ─── GS1 barcode scanning ──────────────────────────────────────────────────

/**
 * Parse a GS1-128 / DataMatrix scan string.
 * Handles fixed-length AIs: 01 (GTIN-14), 17 (expiry YYMMDD), then 10 (lot).
 * Returns { gtin, expiry (Date), lot } or null if the string doesn't match.
 */
// GS1 AI fixed-length lookup (number of data digits after the AI prefix).
// AIs not listed here are treated as variable-length (terminated by GS/FNC1 or end of string).
const GS1_FIXED_LENGTHS = {
    '00': 18, '01': 14, '02': 14,
    '11': 6,  '12': 6,  '13': 6,  '14': 6,  '15': 6,  '16': 6,  '17': 6,  '18': 6,  '19': 6,
    '20': 2,
    '31': 6,  '32': 6,  '33': 6,  '34': 6,  '35': 6,  '36': 6,
    '41': 13,
};

// 2-digit AI prefixes we recognise enough to skip over.
const GS1_KNOWN_AI_PREFIXES = new Set([
    '00','01','02','10','11','12','13','14','15','16','17','18','19',
    '20','21','22','23','24','25','26',
    '30','31','32','33','34','35','36','37',
    '40','41','42','43',
    '70','71','72','73','74','75','76','77','78','79',
    '80','81','82','83','84','85','86','87','88','89',
    '90','91','92','93','94','95','96','97','98','99',
]);

/**
 * Parse a GS1-128 / DataMatrix scan string.
 * Fixed-length AIs are consumed exactly. Variable-length AIs are terminated
 * by a GS (FNC1, \x1d) character — if no GS is present they run to end of string
 * (per GS1 spec: variable-length fields must be FNC1-terminated unless last).
 * Returns { gtin, expiry (Date), lot } or null if required fields not found.
 */
function parseGS1(raw) {
    if (!raw || raw.length < 16) return null;

    // Strip any leading AIM symbology identifier e.g. "]d2", "]Q3"
    const aimPrefix = raw.match(/^\][a-zA-Z]\d/);
    let data = aimPrefix ? raw.substring(3) : raw;

    // Normalise semicolons to the standard GS/FNC1 character — some scanners
    // emit ';' as the group separator for variable-length field termination.
    data = data.replace(/;/g, '\x1d');

    const GS = '\x1d'; // FNC1 separator
    const hasGS = data.includes(GS);

    let pos = 0;
    let gtin = null, expiry = null, lot = null;

    while (pos < data.length) {
        if (data[pos] === GS) { pos++; continue; }
        if (pos + 2 > data.length) break;

        const ai = data.substring(pos, pos + 2);
        if (!GS1_KNOWN_AI_PREFIXES.has(ai)) break;

        pos += 2; // consume AI

        if (GS1_FIXED_LENGTHS[ai] !== undefined) {
            // Fixed-length: consume exactly N chars
            const len = GS1_FIXED_LENGTHS[ai];
            const value = data.substring(pos, pos + len);
            pos += len;

            if (ai === '01') {
                if (value.length === 14 && /^\d{14}$/.test(value)) gtin = value;
            } else if (ai === '17') {
                const yy = parseInt(value.substring(0, 2), 10);
                const mm = parseInt(value.substring(2, 4), 10);
                const dd = parseInt(value.substring(4, 6), 10);
                expiry = dd === 0
                    ? new Date(yy + 2000, mm, 0)        // last day of month
                    : new Date(yy + 2000, mm - 1, dd);
            }
        } else {
            // Variable-length: terminated by GS if present, otherwise end of string
            let end;
            if (hasGS) {
                const gsIdx = data.indexOf(GS, pos);
                end = gsIdx !== -1 ? gsIdx : data.length;
            } else {
                end = data.length;
            }
            const value = data.substring(pos, end);
            pos = end;

            if (ai === '10') lot = value;
            // ai 21 (serial), 22, etc. ignored
        }
    }

    if (!gtin || !expiry || !lot) return null;
    return { gtin, expiry, lot };
}

/** Format a Date as YYYY-MM-DD for use in <input type="date"> */
function formatDateForInput(d) {
    const yyyy = d.getFullYear();
    const mm = String(d.getMonth() + 1).padStart(2, '0');
    const dd = String(d.getDate()).padStart(2, '0');
    return `${yyyy}-${mm}-${dd}`;
}

// Buffer for keyboard-wedge barcode detection
let _scanBuffer = [];
let _scanBufferTimer = null;
let _activeScanLineEl = null; // last delivery line that received focus
let _preScanFocusedInput = null;  // input that had focus when scan started
let _preScanFocusedValue = null;  // its value before any scan chars were typed
const SCAN_MAX_GAP_MS = 50;
const SCAN_MIN_LENGTH = 20;

// Separate buffer for main-screen scan (does not interfere with delivery modal)
let _mainScanBuffer = [];
let _mainScanBufferTimer = null;
let _mainPreScanFocusedInput = null;
let _mainPreScanFocusedValue = null;

function _onMainScreenKeydown(e) {
    // Only act when no modal is open
    if (document.querySelector('.modal.show')) return;

    const now = Date.now();

    if (e.key === 'Enter') {
        const raw = _mainScanBuffer.map(x => x.char).join('');
        _mainScanBuffer = [];
        if (_mainScanBufferTimer) { clearTimeout(_mainScanBufferTimer); _mainScanBufferTimer = null; }

        if (raw.length >= SCAN_MIN_LENGTH) {
            e.preventDefault();
            if (_mainPreScanFocusedInput) {
                _mainPreScanFocusedInput.value = _mainPreScanFocusedValue || '';
            }
            _mainPreScanFocusedInput = null;
            _mainPreScanFocusedValue = null;
            handleMainScreenBarcodeScan(raw);
        }
        return;
    }

    if (e.key.length === 1) {
        const gap = _mainScanBuffer.length > 0 ? now - _mainScanBuffer[_mainScanBuffer.length - 1].time : 0;

        if (_mainScanBuffer.length > 0 && gap > SCAN_MAX_GAP_MS) {
            _mainScanBuffer = [];
            _mainPreScanFocusedInput = null;
            _mainPreScanFocusedValue = null;
        }

        if (_mainScanBuffer.length === 0) {
            const active = document.activeElement;
            if (active && (active.tagName === 'INPUT' || active.tagName === 'TEXTAREA')) {
                _mainPreScanFocusedInput = active;
                _mainPreScanFocusedValue = active.value;
            } else {
                _mainPreScanFocusedInput = null;
                _mainPreScanFocusedValue = null;
            }
        } else {
            e.preventDefault();
        }

        _mainScanBuffer.push({ char: e.key, time: now });

        if (_mainScanBufferTimer) clearTimeout(_mainScanBufferTimer);
        _mainScanBufferTimer = setTimeout(() => {
            _mainScanBuffer = [];
            _mainPreScanFocusedInput = null;
            _mainPreScanFocusedValue = null;
        }, 500);
    }
}

function _onDeliveryModalKeydown(e) {
    // Only act when the receive delivery modal is open
    if (!document.getElementById('receiveDeliveryModal')?.classList.contains('show')) return;

    // Stop intercepting if the GTIN mapping modal is open on top
    if (document.getElementById('gtinMappingModal')?.classList.contains('show')) return;

    // Track which delivery line last had focus
    const focusedLine = document.activeElement?.closest('.delivery-line');
    if (focusedLine) _activeScanLineEl = focusedLine;

    const now = Date.now();

    if (e.key === 'Enter') {
        const raw = _scanBuffer.map(x => x.char).join('');
        _scanBuffer = [];
        if (_scanBufferTimer) { clearTimeout(_scanBufferTimer); _scanBufferTimer = null; }

        // Only treat as a scan if it arrived very fast
        if (raw.length >= SCAN_MIN_LENGTH) {
            e.preventDefault();
            // Restore the focused input to its pre-scan value (remove the 1 char that slipped in)
            if (_preScanFocusedInput) {
                _preScanFocusedInput.value = _preScanFocusedValue || '';
            }
            _preScanFocusedInput = null;
            _preScanFocusedValue = null;
            handleBarcodeScan(raw);
        } else {
        }
        return;
    }

    // Single printable character
    if (e.key.length === 1) {
        const gap = _scanBuffer.length > 0 ? now - _scanBuffer[_scanBuffer.length - 1].time : 0;

        // If gap is too large, start fresh (human typed slowly)
        if (_scanBuffer.length > 0 && gap > SCAN_MAX_GAP_MS) {
            _scanBuffer = [];
            _preScanFocusedInput = null;
            _preScanFocusedValue = null;
        }

        // Save the focused input + its value before the first scan char lands
        if (_scanBuffer.length === 0) {
            const active = document.activeElement;
            if (active && (active.tagName === 'INPUT' || active.tagName === 'TEXTAREA')) {
                _preScanFocusedInput = active;
                _preScanFocusedValue = active.value;
            } else {
                _preScanFocusedInput = null;
                _preScanFocusedValue = null;
            }
        } else {
            // Subsequent rapid chars — suppress them from going into the focused input
            e.preventDefault();
        }

        _scanBuffer.push({ char: e.key, time: now });

        // Auto-clear buffer if Enter never comes
        if (_scanBufferTimer) clearTimeout(_scanBufferTimer);
        _scanBufferTimer = setTimeout(() => {
            _scanBuffer = [];
            _preScanFocusedInput = null;
            _preScanFocusedValue = null;
        }, 500);
    }
}

async function handleMainScreenBarcodeScan(raw) {
    const parsed = parseGS1(raw);
    if (!parsed) {
        showToast('Barcode not recognised as a GS1 code', 'warning');
        return;
    }

    const { gtin, lot } = parsed;

    let mapping = null;
    try {
        const resp = await apiCall(`/gtin/${encodeURIComponent(gtin)}`);
        if (resp.ok) {
            mapping = await resp.json();
        } else if (resp.status !== 404) {
            throw new Error(`Server error ${resp.status}`);
        }
    } catch (err) {
        showToast('Failed to look up barcode: ' + err.message, 'error');
        return;
    }

    if (!mapping) {
        showToast('Unknown barcode — scan it in a delivery first to map it to a drug', 'warning');
        return;
    }

    const drugId = mapping.drug_id;
    const variantId = mapping.drug_variant_id;

    // Expand drug + variant
    expandedDrugs.add(drugId);
    expandedVariants.add(variantId);

    // Ensure detail + batch data are loaded
    await ensureDrugDetailLoaded(drugId);
    if (!loadedVariantBatches.has(variantId)) {
        try {
            const resp = await apiCall(`/variants/${variantId}/batches`);
            if (resp.ok) loadedVariantBatches.set(variantId, await resp.json());
        } catch (_) { /* non-fatal */ }
    }

    // Set highlight
    if (_highlightClearTimer) { clearTimeout(_highlightClearTimer); _highlightClearTimer = null; }
    _highlightedBatchLot = lot;
    _highlightedVariantId = variantId;

    renderDrugs();

    requestAnimationFrame(() => scrollToHighlightedBatch());

    // Auto-clear highlight after 5 seconds
    _highlightClearTimer = setTimeout(() => {
        _highlightedBatchLot = null;
        _highlightedVariantId = null;
        _highlightClearTimer = null;
        renderDrugs();
    }, 5000);

    // Confirm to user
    const batches = loadedVariantBatches.get(variantId) || [];
    const found = batches.some(b => b.batch_number === lot);
    if (found) {
        showToast(`${mapping.drug_name} ${mapping.variant_strength} — lot ${lot}`, 'success');
    } else {
        showToast(`${mapping.drug_name} ${mapping.variant_strength} — lot ${lot} (no active stock)`, 'warning');
    }
}

function scrollToHighlightedBatch() {
    if (!_highlightedBatchLot || _highlightedVariantId == null) return;
    const el = document.querySelector(`[data-batch-number="${CSS.escape(_highlightedBatchLot)}"][data-variant-id="${_highlightedVariantId}"]`);
    if (el) el.scrollIntoView({ behavior: 'smooth', block: 'center' });
}

async function handleBarcodeScan(raw) {
    const parsed = parseGS1(raw);
    if (!parsed) {
        showToast('Barcode not recognised as a GS1 code', 'warning');
        return;
    }

    const { gtin, expiry, lot } = parsed;
    const expiryStr = formatDateForInput(expiry);

    // Look up GTIN mapping
    let mapping = null;
    try {
        const resp = await apiCall(`/gtin/${encodeURIComponent(gtin)}`);
        if (resp.ok) {
            mapping = await resp.json();
        } else if (resp.status !== 404) {
            throw new Error(`Server error ${resp.status}`);
        }
    } catch (err) {
        showToast('Failed to look up barcode: ' + err.message, 'error');
        return;
    }

    if (!mapping) {
        // Unknown GTIN — open mapping modal then re-process
        openGtinMappingModal(gtin, expiryStr, lot);
        return;
    }

    await _applyBarcodeScanToLines(mapping, lot, expiryStr);
}

async function _applyBarcodeScanToLines(mapping, lot, expiryStr) {
    const container = document.getElementById('deliveryLinesContainer');
    if (!container) return;

    const lines = Array.from(container.querySelectorAll('.delivery-line'));

    // 1. Find an existing line with the same variant + lot + expiry → increment pack count
    for (const line of lines) {
        const variantId = line.querySelector('.delivery-variant-select')?.value;
        const batchVal = line.querySelector('.delivery-batch-number')?.value?.trim();
        const expiryVal = line.querySelector('.delivery-expiry-date')?.value;

        if (
            String(variantId) === String(mapping.drug_variant_id) &&
            batchVal === lot &&
            expiryVal === expiryStr
        ) {
            const countInput = line.querySelector('.delivery-pack-count');
            const current = parseFloat(countInput.value) || 0;
            countInput.value = current + 1;
            updateDeliveryLineQuantityDisplay(line);
            showToast(`Pack count incremented to ${current + 1} for lot ${lot}`, 'success');
            return;
        }
    }

    // 2. Find any existing empty line (lot and expiry both blank) — never overwrite a filled line
    const emptyLine = lines.find(l => {
        const batch = l.querySelector('.delivery-batch-number')?.value?.trim();
        const expiry = l.querySelector('.delivery-expiry-date')?.value;
        return !batch && !expiry;
    }) || null;

    if (emptyLine) {
        await _populateDeliveryLine(emptyLine, mapping, lot, expiryStr);
        return;
    }

    // 3. Append a new line
    appendDeliveryLine();
    const newLine = container.querySelector('.delivery-line:last-child');
    if (newLine) await _populateDeliveryLine(newLine, mapping, lot, expiryStr);
}

async function _populateDeliveryLine(line, mapping, lot, expiryStr) {
    const drugSelect = line.querySelector('.delivery-drug-select');
    const variantSelect = line.querySelector('.delivery-variant-select');
    const packSelect = line.querySelector('.delivery-pack-select');
    const batchInput = line.querySelector('.delivery-batch-number');
    const expiryInput = line.querySelector('.delivery-expiry-date');
    const packCountInput = line.querySelector('.delivery-pack-count');

    if (drugSelect) {
        drugSelect.innerHTML = buildDeliveryDrugOptions(mapping.drug_id);
        drugSelect.value = String(mapping.drug_id);
    }

    // Ensure drug detail (with packs) is loaded before trying to populate pack select
    await ensureDrugDetailLoaded(mapping.drug_id);

    if (variantSelect) {
        const drug = allDrugs.find(d => d.id === mapping.drug_id) || null;
        variantSelect.innerHTML = buildDeliveryVariantOptions(drug, mapping.drug_variant_id);
        variantSelect.value = String(mapping.drug_variant_id);
        const variant = getVariantById(mapping.drug_variant_id);
        if (packSelect) {
            packSelect.innerHTML = buildDeliveryPackOptions(variant, mapping.variant_pack_id);
            packSelect.value = String(mapping.variant_pack_id);
        }
    }

    if (batchInput) batchInput.value = lot;
    if (expiryInput) expiryInput.value = expiryStr;
    if (packCountInput && !packCountInput.value) packCountInput.value = 1;

    updateDeliveryLineQuantityDisplay(line);
    showToast(`Populated: ${mapping.drug_name} ${mapping.variant_strength} — lot ${lot}`, 'success');
}

function _detachDeliveryBarcodeListener() {
    const modalEl = document.getElementById('receiveDeliveryModal');
    if (modalEl?._barcodeListener) {
        document.removeEventListener('keydown', modalEl._barcodeListener);
        modalEl._barcodeListener = null;
    }
    _scanBuffer = [];
    _activeScanLineEl = null;
}

function _refreshGtinMappingSelects() {
    // Kept for compatibility — delegates to reinit with current selections
    const drugId = parseInt(document.getElementById('gtinMappingDrugSelect')?.value || '', 10) || null;
    const variantId = parseInt(document.getElementById('gtinMappingVariantSelect')?.value || '', 10) || null;
    const packId = parseInt(document.getElementById('gtinMappingPackSelect')?.value || '', 10) || null;
    _reinitGtinMappingModal({ drugId, variantId, packId });
}

// Reinitialise the GTIN mapping modal dropdowns from fresh allDrugs data,
// optionally pre-selecting specific drug/variant/pack IDs.
async function _reinitGtinMappingModal(restore) {
    const drugSelect = document.getElementById('gtinMappingDrugSelect');
    const variantSelect = document.getElementById('gtinMappingVariantSelect');
    const packSelect = document.getElementById('gtinMappingPackSelect');
    if (!drugSelect) return;

    // Rebuild drug list
    drugSelect.innerHTML = '<option value="">-- Select drug --</option>' +
        allDrugs.map(d => `<option value="${d.id}">${escapeHtml(d.name)}</option>`).join('');

    const drugId = restore?.drugId || null;
    const variantId = restore?.variantId || null;
    const packId = restore?.packId || null;

    // If no drug to restore, clear cascades and stop
    if (!drugId) {
        variantSelect.innerHTML = '<option value="">-- Select variant --</option>';
        packSelect.innerHTML = '<option value="">-- Select pack --</option>';
        return;
    }

    drugSelect.value = String(drugId);
    await ensureDrugDetailLoaded(drugId);
    const drug = allDrugs.find(d => d.id === drugId);

    // Rebuild variant list
    variantSelect.innerHTML = '<option value="">-- Select variant --</option>';
    if (drug) {
        variantSelect.innerHTML += drug.variants.map(v =>
            `<option value="${v.id}">${escapeHtml(v.strength)} (${escapeHtml(v.unit)})</option>`
        ).join('');
    }

    if (!variantId) {
        packSelect.innerHTML = '<option value="">-- Select pack --</option>';
        return;
    }

    variantSelect.value = String(variantId);
    const variant = getVariantById(variantId); // checks loadedDrugDetails first (has packs)

    // Rebuild pack list
    packSelect.innerHTML = '<option value="">-- Select pack --</option>';
    if (variant) {
        const packs = getActivePacksForVariant(variant);
        packSelect.innerHTML += packs.map(p =>
            `<option value="${p.id}">${escapeHtml(packLabel(p))}</option>`
        ).join('');
        if (packId) packSelect.value = String(packId);
    }
}

function gtinMappingAddDrug() {
    // Snapshot current drug IDs. handleAddDrug will call loadDrugs() once (we intercept it
    // to find the new drug ID), then open addVariantModal. We hook the *subsequent* loadDrugs
    // call (from handleAddVariant) to reinit the GTIN modal with drug+variant selected.
    _gtinMappingWaitingForNewDrug = new Set(allDrugs.map(d => d.id));
    openModal(document.getElementById('addModal'));
}

function gtinMappingAddVariant() {
    const drugId = parseInt(document.getElementById('gtinMappingDrugSelect').value || '', 10);
    if (!drugId) { showToast('Select a drug first', 'warning'); return; }
    const drug = allDrugs.find(d => d.id === drugId);
    const existingVariantIds = new Set((drug?.variants || []).map(v => v.id));
    // After reload, find the new variant by diffing
    _gtinMappingPendingRestore = { drugId, variantId: null, packId: null, _existingVariantIds: existingVariantIds };
    _gtinMappingPendingRefresh = true;
    openAddVariantModal(drugId);
}

function gtinMappingAddPack() {
    const variantId = parseInt(document.getElementById('gtinMappingVariantSelect').value || '', 10);
    if (!variantId) { showToast('Select a variant first', 'warning'); return; }
    const drugId = parseInt(document.getElementById('gtinMappingDrugSelect').value || '', 10);
    if (!drugId) return;
    // Use getVariantById which returns the detail variant (with packs) if loaded
    const variant = getVariantById(variantId);
    const existingPackIds = new Set((getActivePacksForVariant(variant) || []).map(p => p.id));
    _gtinMappingPendingRestore = { drugId, variantId, packId: null, _existingPackIds: existingPackIds };
    _gtinMappingPendingRefresh = true;
    deliveryDrugId = drugId;
    _gtinMappingPendingVariantId = variantId;
    openAddPackSizeFromDeliveryModal();
}

// ─── GTIN mapping modal logic ──────────────────────────────────────────────

let _pendingGtinScan = null; // { gtin, expiryStr, lot } while mapping modal is open

function openGtinMappingModal(gtin, expiryStr, lot) {
    _pendingGtinScan = { gtin, expiryStr, lot };

    document.getElementById('gtinMappingGtin').value = gtin;

    // Populate drug selector from allDrugs
    const drugSelect = document.getElementById('gtinMappingDrugSelect');
    drugSelect.innerHTML = '<option value="">-- Select drug --</option>' +
        allDrugs.map(d => `<option value="${d.id}">${escapeHtml(d.name)}</option>`).join('');

    document.getElementById('gtinMappingVariantSelect').innerHTML = '<option value="">-- Select variant --</option>';
    document.getElementById('gtinMappingPackSelect').innerHTML = '<option value="">-- Select pack --</option>';

    openModal(document.getElementById('gtinMappingModal'));
}

async function onGtinMappingDrugChange() {
    const drugId = parseInt(document.getElementById('gtinMappingDrugSelect').value || '', 10);
    const variantSelect = document.getElementById('gtinMappingVariantSelect');
    const packSelect = document.getElementById('gtinMappingPackSelect');

    variantSelect.innerHTML = '<option value="">-- Select variant --</option>';
    packSelect.innerHTML = '<option value="">-- Select pack --</option>';

    if (!drugId) return;
    await ensureDrugDetailLoaded(drugId);
    const drug = allDrugs.find(d => d.id === drugId);
    if (!drug) return;
    variantSelect.innerHTML += drug.variants.map(v =>
        `<option value="${v.id}">${escapeHtml(v.strength)} (${escapeHtml(v.unit)})</option>`
    ).join('');
}

function onGtinMappingVariantChange() {
    const variantId = parseInt(document.getElementById('gtinMappingVariantSelect').value || '', 10);
    const variant = getVariantById(variantId); // checks loadedDrugDetails first (has packs)
    const packSelect = document.getElementById('gtinMappingPackSelect');

    packSelect.innerHTML = '<option value="">-- Select pack --</option>';
    if (!variant) return;

    const packs = getActivePacksForVariant(variant);
    packSelect.innerHTML += packs.map(p =>
        `<option value="${p.id}">${escapeHtml(packLabel(p))}</option>`
    ).join('');
}

async function handleSaveGtinMapping() {
    if (!_pendingGtinScan) return;

    const variantId = parseInt(document.getElementById('gtinMappingVariantSelect').value || '', 10);
    const packId = parseInt(document.getElementById('gtinMappingPackSelect').value || '', 10);

    if (!variantId || !packId) {
        showToast('Please select a variant and pack', 'warning');
        return;
    }

    try {
        const resp = await apiCall('/gtin', {
            method: 'POST',
            body: JSON.stringify({
                gtin: _pendingGtinScan.gtin,
                drug_variant_id: variantId,
                variant_pack_id: packId,
            }),
        });

        if (!resp.ok) {
            const err = await resp.json();
            throw new Error(err.detail || 'Failed to save GTIN mapping');
        }

        const mapping = await resp.json();
        closeModal(document.getElementById('gtinMappingModal'));
        showToast(`GTIN mapped to ${mapping.drug_name} ${mapping.variant_strength}`, 'success');

        // Now apply the scan that triggered this
        _applyBarcodeScanToLines(mapping, _pendingGtinScan.lot, _pendingGtinScan.expiryStr);
        _pendingGtinScan = null;
    } catch (err) {
        showToast('Error saving GTIN: ' + err.message, 'error');
    }
}

function buildDeliveryDrugOptions(selectedDrugId = '') {
    return [
        '<option value="">-- Select drug --</option>',
        ...allDrugs.map(d => {
            const sel = String(d.id) === String(selectedDrugId) ? ' selected' : '';
            return `<option value="${d.id}"${sel}>${escapeHtml(d.name)}</option>`;
        })
    ].join('');
}

function appendDeliveryLine(prefill = {}) {
    const container = document.getElementById('deliveryLinesContainer');
    if (!container) return;

    deliveryLineCounter += 1;
    const lineId = `delivery-line-${deliveryLineCounter}`;

    const line = document.createElement('div');
    line.className = 'delivery-line';
    line.dataset.lineId = lineId;

    const initialDrug = prefill.drugId ? allDrugs.find(d => String(d.id) === String(prefill.drugId)) || null : null;
    const initialDrugId = prefill.drugId || '';
    const initialVariant = prefill.variantId && initialDrug
        ? initialDrug.variants.find(v => String(v.id) === String(prefill.variantId)) || null
        : null;
    const initialVariantId = prefill.variantId || '';
    const initialPackId = prefill.packId || (initialVariant && getActivePacksForVariant(initialVariant).length === 1 ? getActivePacksForVariant(initialVariant)[0].id : '');
    const initialPackCount = prefill.packCount || '';

    line.innerHTML = `
        <div class="delivery-line-grid">
            <div class="form-group">
                <label>Drug</label>
                <select class="delivery-drug-select" required>
                    ${buildDeliveryDrugOptions(initialDrugId)}
                </select>
            </div>
            <div class="form-group">
                <label>Variant</label>
                <select class="delivery-variant-select" required>
                    ${buildDeliveryVariantOptions(initialDrug, initialVariantId)}
                </select>
            </div>
            <div class="form-group">
                <label>Pack Type</label>
                <select class="delivery-pack-select" required>
                    ${buildDeliveryPackOptions(initialVariant, initialPackId)}
                </select>
            </div>
            <div class="form-group">
                <label>Pack Count</label>
                <input type="number" class="delivery-pack-count" min="1" step="1" value="${initialPackCount}" required>
            </div>
            <div class="form-group">
                <label>Batch Number</label>
                <input type="text" class="delivery-batch-number" value="${prefill.batchNumber || ''}" placeholder="e.g. ABC123" required>
            </div>
            <div class="form-group">
                <label>Expiry</label>
                <input type="date" class="delivery-expiry-date" value="${prefill.expiryDate || ''}" required>
            </div>
            <div class="form-group">
                <label>Location</label>
                <select class="delivery-location-select" required>
                    ${buildDeliveryLocationOptions(prefill.locationId || '')}
                </select>
            </div>
            <button type="button" class="btn btn-danger btn-small delivery-remove-btn">Remove</button>
        </div>
    `;

    const removeBtn = line.querySelector('.delivery-remove-btn');
    if (removeBtn) {
        removeBtn.addEventListener('click', () => {
            if (container.children.length <= 1) {
                showToast('At least one delivery line is required', 'warning');
                return;
            }
            line.remove();
        });
    }

    wireDeliveryLineEvents(line);
    updateDeliveryLineQuantityDisplay(line);

    container.appendChild(line);
}

function refreshDeliveryVariantSelects() {
    const container = document.getElementById('deliveryLinesContainer');
    if (!container) return;

    container.querySelectorAll('.delivery-line').forEach(line => {
        const drugSelect = line.querySelector('.delivery-drug-select');
        const variantSelect = line.querySelector('.delivery-variant-select');
        const packSelect = line.querySelector('.delivery-pack-select');
        if (!variantSelect) return;

        const drugId = parseInt(drugSelect?.value || '', 10);
        const drug = allDrugs.find(d => d.id === drugId) || null;
        const currentVariantId = variantSelect.value;
        variantSelect.innerHTML = buildDeliveryVariantOptions(drug, currentVariantId);

        const variant = getVariantById(parseInt(variantSelect.value || '', 10));
        if (packSelect) {
            const currentPackId = packSelect.value;
            packSelect.innerHTML = buildDeliveryPackOptions(variant, currentPackId);
        }

        updateDeliveryLineQuantityDisplay(line);
    });
}

async function initializeDeliveryLocations() {
    try {
        const response = await apiCall('/locations');
        if (!response.ok) throw new Error('Failed to load locations');
        const locations = await response.json();
        deliveryLocations = locations.filter(location => location.is_active);
    } catch (error) {
        console.error('Error loading delivery locations:', error);
        showToast('Failed to load storage locations', 'error');
        deliveryLocations = [];
    }
}

async function openReceiveDeliveryModal() {
    deliveryDrugId = null;

    const form = document.getElementById('receiveDeliveryForm');
    const container = document.getElementById('deliveryLinesContainer');
    const label = document.getElementById('receiveDeliveryDrugLabel');

    if (form) form.reset();
    if (container) container.innerHTML = '';
    if (label) label.textContent = 'Scan items or add lines manually';

    await initializeDeliveryLocations();
    appendDeliveryLine();

    // Attach barcode scanner listener
    _activeScanLineEl = null;
    _scanBuffer = [];
    const modalEl = document.getElementById('receiveDeliveryModal');
    if (modalEl._barcodeListener) document.removeEventListener('keydown', modalEl._barcodeListener);
    modalEl._barcodeListener = _onDeliveryModalKeydown;
    document.addEventListener('keydown', modalEl._barcodeListener);

    openModal(modalEl);
}

function handleAddVariantFromDelivery() {
    if (!deliveryDrugId) {
        const deliveryContainer = document.getElementById('deliveryLinesContainer');
        const firstDrugIdStr = deliveryContainer
            ? Array.from(deliveryContainer.querySelectorAll('.delivery-drug-select')).map(s => s.value).find(v => v)
            : null;
        deliveryDrugId = firstDrugIdStr ? parseInt(firstDrugIdStr, 10) : null;
    }
    if (!deliveryDrugId) {
        showToast('Select a drug on a delivery line first', 'warning');
        return;
    }
    openAddVariantModal(deliveryDrugId);
}

function openAddPackSizeFromDeliveryModal() {
    if (!deliveryDrugId) {
        // In multi-drug mode, get drug from the first line that has one selected
        const deliveryContainer = document.getElementById('deliveryLinesContainer');
        const firstDrugIdStr = deliveryContainer
            ? Array.from(deliveryContainer.querySelectorAll('.delivery-drug-select')).map(s => s.value).find(v => v)
            : null;
        deliveryDrugId = firstDrugIdStr ? parseInt(firstDrugIdStr, 10) : null;
    }

    if (!deliveryDrugId) {
        showToast('Select a drug on a delivery line first', 'warning');
        return;
    }
    const drug = allDrugs.find(d => d.id === deliveryDrugId);
    if (!drug) {
        showToast('Drug not found', 'error');
        return;
    }

    const form = document.getElementById('addPackSizeForm');
    if (form) form.reset();

    const label = document.getElementById('addPackSizeDrugLabel');
    if (label) label.textContent = `Drug: ${drug.name}`;

    // Try to pre-select variant from first delivery line that has one chosen
    const deliveryContainer = document.getElementById('deliveryLinesContainer');
    const selectedDeliveryVariantId = deliveryContainer
        ? (Array.from(deliveryContainer.querySelectorAll('.delivery-variant-select'))
            .map(s => s.value)
            .find(v => v)) || ''
        : '';

    const variantSelect = document.getElementById('addPackSizeVariantSelect');
    if (variantSelect) {
        variantSelect.innerHTML = [
            '<option value="">-- Select variant --</option>',
            ...drug.variants.map(v =>
                `<option value="${v.id}">${escapeHtml(v.strength)} (${escapeHtml(v.unit)})</option>`
            )
        ].join('');
        if (selectedDeliveryVariantId) {
            variantSelect.value = selectedDeliveryVariantId;
        } else if (drug.variants.length === 1) {
            variantSelect.value = String(drug.variants[0].id);
        }
    }

    // Update the hint for the pre-selected variant
    const selectedId = parseInt(variantSelect?.value || '', 10);
    const selectedVariant = getVariantById(selectedId);
    const hint = document.getElementById('addPackSizeHint');
    if (hint) hint.textContent = selectedVariant ? `Base unit: ${selectedVariant.unit}` : '';

    // Reset pack type default to box
    const packTypeSelect = document.getElementById('addPackSizeType');
    if (packTypeSelect) packTypeSelect.value = 'box';

    openModal(document.getElementById('addPackSizeModal'));
}

async function handleAddPackSize(e) {
    e.preventDefault();

    const variantId = parseInt(document.getElementById('addPackSizeVariantSelect')?.value || '', 10);
    const packType = (document.getElementById('addPackSizeType')?.value || 'box').trim();
    const packSize = parseFloat(document.getElementById('addPackSizeCount')?.value || '');

    if (!variantId) {
        showToast('Please select a variant', 'warning');
        return;
    }
    if (!packSize || packSize <= 0) {
        showToast('Please enter a valid pack size greater than zero', 'warning');
        return;
    }

    try {
        const response = await apiCall(`/variants/${variantId}/packs`, {
            method: 'POST',
            body: JSON.stringify({
                pack_unit_name: packType,
                pack_size_in_base_units: packSize,
                is_active: true
            })
        });

        if (!response.ok) {
            const error = await response.json();
            throw new Error(error.detail || 'Failed to add pack size');
        }

        closeModal(document.getElementById('addPackSizeModal'));
        // Invalidate drug detail cache so the new pack will be re-fetched on next expand
        const packDrugId = allDrugs.find(d => (d.variants || []).some(v => v.id === variantId))?.id;
        if (packDrugId) loadedDrugDetails.delete(packDrugId);
        await loadDrugs();
        // Refresh delivery line pack selects so the new pack is immediately available
        refreshDeliveryVariantSelects();
        showToast('Pack size added successfully!', 'success');
    } catch (error) {
        console.error('Error adding pack size:', error);
        showToast('Failed to add pack size: ' + error.message, 'error');
    }
}

async function handleReceiveDelivery(e) {
    e.preventDefault();

    const container = document.getElementById('deliveryLinesContainer');
    if (!container) {
        showToast('Delivery context unavailable', 'error');
        return;
    }

    const lines = Array.from(container.querySelectorAll('.delivery-line'));
    if (lines.length === 0) {
        showToast('Add at least one delivery line', 'warning');
        return;
    }

    const payloads = [];

    for (let i = 0; i < lines.length; i += 1) {
        const line = lines[i];
        const variantId = parseInt(line.querySelector('.delivery-variant-select')?.value || '', 10);
        const packIdRaw = line.querySelector('.delivery-pack-select')?.value || '';
        const packId = packIdRaw ? parseInt(packIdRaw, 10) : null;
        const packCountRaw = line.querySelector('.delivery-pack-count')?.value || '';
        const packCount = packCountRaw ? parseFloat(packCountRaw) : null;
        const batchNumber = (line.querySelector('.delivery-batch-number')?.value || '').trim();
        const expiryDate = line.querySelector('.delivery-expiry-date')?.value || '';
        const locationId = parseInt(line.querySelector('.delivery-location-select')?.value || '', 10);

        if (!variantId || !packId || packCount === null || Number.isNaN(packCount) || packCount <= 0 || !batchNumber || !expiryDate || !locationId) {
            showToast(`Delivery line ${i + 1} is incomplete`, 'warning');
            return;
        }

        if (Math.abs(packCount - Math.round(packCount)) > 1e-6) {
            showToast(`Delivery line ${i + 1} pack count must be a whole number`, 'warning');
            return;
        }

        const variant = getVariantById(variantId);
        const selectedPack = variant ? getActivePacksForVariant(variant).find(pack => pack.id === packId) : null;
        if (!selectedPack) {
            showToast(`Delivery line ${i + 1} has an invalid pack selection`, 'warning');
            return;
        }
        const computedQuantity = packCount * selectedPack.pack_size_in_base_units;

        payloads.push({
            variantId,
            payload: {
                batch_number: batchNumber,
                received_pack_id: packId,
                received_pack_count: packCount,
                expiry_date: expiryDate,
                location_id: locationId,
                notes: `Received ${packCount} ${selectedPack.pack_unit_name}(s), total ${computedQuantity} ${variant ? variant.unit : 'units'}`
            }
        });
    }

    try {
        for (let i = 0; i < payloads.length; i += 1) {
            const entry = payloads[i];
            const response = await apiCall(`/variants/${entry.variantId}/batches`, {
                method: 'POST',
                body: JSON.stringify(entry.payload)
            });

            if (!response.ok) {
                const error = await response.json();
                throw new Error(`Line ${i + 1}: ${error.detail || 'Failed to receive delivery line'}`);
            }
        }

        closeModal(document.getElementById('receiveDeliveryModal'));
        _detachDeliveryBarcodeListener();
        // Invalidate batch cache for all delivered variants
        payloads.forEach(entry => loadedVariantBatches.delete(entry.variantId));
        await loadDrugs();
        showToast(`Delivery received successfully (${payloads.length} line${payloads.length === 1 ? '' : 's'})`, 'success');
    } catch (error) {
        console.error('Error receiving delivery:', error);
        showToast('Failed to receive delivery: ' + error.message, 'error');
    }
}