From 7254719794b1792f3efdb9103f2279d7e92072ea Mon Sep 17 00:00:00 2001
From: James Pattinson <james@pattinson.org>
Date: Thu, 18 Jun 2026 18:39:26 +0100
Subject: [PATCH] fix zero handling

---
 README.md                       | 14 +++++++
 app/collector.py                |  8 ++++
 scripts/remove_zero_readings.sh | 68 +++++++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+)
 create mode 100755 scripts/remove_zero_readings.sh

diff --git a/README.md b/README.md
index c8cad19..54d11a9 100644
--- a/README.md
+++ b/README.md
@@ -46,6 +46,20 @@ Compose builds the internal database URL from `MYSQL_USER`, `MYSQL_PASSWORD`,
 and `MYSQL_DATABASE`. Set `DATABASE_URL` only if you want to point the app at a
 different database.
 
+## Maintenance
+
+Remove bad readings where temperature, humidity, and battery are all zero:
+
+```sh
+scripts/remove_zero_readings.sh
+```
+
+Preview the count without deleting:
+
+```sh
+scripts/remove_zero_readings.sh --dry-run
+```
+
 ## Reports
 
 Open `/reports` in the web app to generate a date-range summary. Use the
diff --git a/app/collector.py b/app/collector.py
index 531de54..773981a 100644
--- a/app/collector.py
+++ b/app/collector.py
@@ -24,6 +24,10 @@ logger = logging.getLogger(__name__)
 SENSOR_DEVICE_TYPES = {"WoIOSensor"}
 
 
+def is_all_zero_reading(status: dict[str, Any]) -> bool:
+    return status.get("temperature") == 0 and status.get("humidity") == 0 and status.get("battery") == 0
+
+
 def upsert_device(device_data: dict[str, Any]) -> None:
     device_id = device_data["deviceId"]
     with session_scope() as session:
@@ -55,6 +59,10 @@ def save_reading(device: Device, status: dict[str, Any]) -> None:
         logger.info("Skipping %s (%s): status has no temperature/humidity", device.name, device.id)
         return
 
+    if is_all_zero_reading(status):
+        logger.info("Skipping %s (%s): status is all zeros", device.name, device.id)
+        return
+
     reading = Reading(
         device_id=device.id,
         recorded_at=datetime.now(timezone.utc).replace(tzinfo=None),
diff --git a/scripts/remove_zero_readings.sh b/scripts/remove_zero_readings.sh
new file mode 100755
index 0000000..4b4d939
--- /dev/null
+++ b/scripts/remove_zero_readings.sh
@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+usage() {
+  cat <<'USAGE'
+Usage: scripts/remove_zero_readings.sh [--dry-run] [--yes]
+
+Removes readings where temperature, humidity, and battery are all zero.
+
+Options:
+  --dry-run   Count matching readings without deleting them.
+  --yes       Delete without prompting.
+  --help      Show this help.
+USAGE
+}
+
+dry_run=0
+assume_yes=0
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --dry-run)
+      dry_run=1
+      ;;
+    --yes|-y)
+      assume_yes=1
+      ;;
+    --help|-h)
+      usage
+      exit 0
+      ;;
+    *)
+      echo "Unknown option: $1" >&2
+      usage >&2
+      exit 2
+      ;;
+  esac
+  shift
+done
+
+where_clause="temperature = 0 AND humidity = 0 AND battery = 0"
+
+run_mysql() {
+  docker compose exec -T db sh -c 'MYSQL_PWD="$MYSQL_PASSWORD" exec mysql -u"$MYSQL_USER" "$MYSQL_DATABASE" "$@"' sh "$@"
+}
+
+matching_count=$(
+  printf 'SELECT COUNT(*) FROM readings WHERE %s;\n' "$where_clause" | run_mysql --batch --skip-column-names
+)
+
+echo "Found ${matching_count} all-zero reading(s)."
+
+if [[ "$dry_run" -eq 1 || "$matching_count" -eq 0 ]]; then
+  exit 0
+fi
+
+if [[ "$assume_yes" -ne 1 ]]; then
+  read -r -p "Delete these readings? Type 'yes' to continue: " answer
+  if [[ "$answer" != "yes" ]]; then
+    echo "No records deleted."
+    exit 0
+  fi
+fi
+
+printf 'DELETE FROM readings WHERE %s;\nSELECT ROW_COUNT();\n' "$where_clause" |
+  run_mysql --batch --skip-column-names |
+  tail -n 1 |
+  xargs printf 'Deleted %s all-zero reading(s).\n'