GS1 scanning and workflow improvements

backend/app/main.py

@@ -1670,7 +1670,41 @@ def create_variant_batch(variant_id: int, payload: BatchCreate, db: Session = De
         .first()
     )
     if existing:
-        raise HTTPException(status_code=400, detail="Batch number already exists for this variant")
+        if existing.expiry_date != payload.expiry_date:
+            raise HTTPException(
+                status_code=400,
+                detail="Batch number already exists for this variant with a different expiry date",
+            )
+
+        # Same batch number and expiry — restock the existing batch
+        existing.quantity += batch_quantity
+        if existing.received_pack_id == resolved["pack_id"]:
+            existing.received_pack_count = (existing.received_pack_count or 0) + resolved["pack_count"]
+        if payload.notes:
+            existing.notes = (existing.notes + "\n" + payload.notes) if existing.notes else payload.notes
+        recompute_batch_pack_state(existing)
+        variant.quantity += batch_quantity
+
+        write_audit_log(
+            db,
+            action="batch.restock",
+            entity_type="batch",
+            entity_id=existing.id,
+            actor=current_user,
+            details={
+                "variant_id": variant_id,
+                "batch_number": batch_number,
+                "quantity_added": batch_quantity,
+                "new_total_quantity": existing.quantity,
+                "received_pack_id": resolved["pack_id"],
+                "received_pack_count": resolved["pack_count"],
+                "expiry_date": str(payload.expiry_date),
+                "location_id": existing.location_id,
+            },
+        )
+        db.commit()
+        db.refresh(existing)
+        return serialize_batch_response(db, existing)
 
     row = Batch(
         drug_variant_id=variant_id,