Add absent_count column and commented-out grace period threshold for tripwire resets

net_alerter/net_alerter.py

@@ -17,6 +17,10 @@ from datetime import datetime, timezone
 from pathlib import Path
 
 # --- Config (overridable via env) ---
+# Minimum consecutive missed scans before a device is considered gone and the
+# tripwire resets. Uncomment to enable — set to 3 for 15-min grace at 5-min cron.
+# ABSENT_THRESHOLD = int(os.getenv("NET_ALERTER_ABSENT_THRESHOLD", "3"))
+
 MATRIX_HOMESERVER = os.getenv("MATRIX_HOMESERVER", "https://m.example.org")
 MATRIX_ACCESS_TOKEN = os.getenv("MATRIX_ACCESS_TOKEN", "")
 MATRIX_ROOM_ID = os.getenv("MATRIX_ROOM_ID", "!REDACTED:example.org")
@@ -50,6 +54,9 @@ def get_db() -> sqlite3.Connection:
         conn.execute("ALTER TABLE devices ADD COLUMN is_present INTEGER NOT NULL DEFAULT 1")
     if "last_left" not in existing:
         conn.execute("ALTER TABLE devices ADD COLUMN last_left TEXT")
+    # absent_count tracks consecutive missed scans (used by ABSENT_THRESHOLD)
+    if "absent_count" not in existing:
+        conn.execute("ALTER TABLE devices ADD COLUMN absent_count INTEGER NOT NULL DEFAULT 0")
     conn.commit()
     return conn
 
@@ -231,19 +238,29 @@ def run() -> None:
                 if not baseline_mode:
                     alerts.append(("REJOIN", d))
             else:
-                # Already present — just update last_seen
+                # Already present — just update last_seen, reset absent_count
                 conn.execute(
-                    "UPDATE devices SET ip=?, name=?, last_seen=? WHERE mac=?",
+                    "UPDATE devices SET ip=?, name=?, last_seen=?, absent_count=0 WHERE mac=?",
                     (d["ip"], d["name"], ts, mac),
                 )
 
-    # Mark devices that were present but didn't appear in this scan as gone
+    # Mark devices that were present but didn't appear in this scan as gone.
+    # absent_count increments each missed scan; is_present flips to 0 immediately
+    # (or after ABSENT_THRESHOLD consecutive misses if that option is enabled).
     present_in_db = {
-        row[0] for row in conn.execute("SELECT mac FROM devices WHERE is_present=1")
+        row[0]: row[1]
+        for row in conn.execute("SELECT mac, absent_count FROM devices WHERE is_present=1")
     }
-    for mac in present_in_db - set(scan_results.keys()):
+    for mac, absent_count in present_in_db.items():
+        if mac in scan_results:
+            continue
+        new_count = absent_count + 1
+        # Uncomment the block below (and ABSENT_THRESHOLD above) to add a grace period:
+        # if new_count < ABSENT_THRESHOLD:
+        #     conn.execute("UPDATE devices SET absent_count=? WHERE mac=?", (new_count, mac))
+        #     continue
         conn.execute(
-            "UPDATE devices SET is_present=0, last_left=? WHERE mac=?",
+            "UPDATE devices SET is_present=0, last_left=?, absent_count=0 WHERE mac=?",
             (ts, mac),
         )
         print(f"[info] Device left: {mac}", file=sys.stderr)