Pull count of detection events by label into prometheus metrics (#20119)

* pull count of detection events by label into prometheus metrics

* format changes with ruff

* remove unneeded f-string

* fix imports format

---------

Co-authored-by: iesad <iesad>

frigate/api/app.py

@@ -11,7 +11,7 @@ from datetime import datetime, timedelta
 from functools import reduce
 from io import StringIO
 from pathlib import Path as FilePath
-from typing import Any, Optional
+from typing import Any, Dict, List, Optional
 
 import aiofiles
 import requests
@@ -21,7 +21,7 @@ from fastapi.encoders import jsonable_encoder
 from fastapi.params import Depends
 from fastapi.responses import JSONResponse, PlainTextResponse, StreamingResponse
 from markupsafe import escape
-from peewee import SQL, operator
+from peewee import SQL, fn, operator
 from pydantic import ValidationError
 
 from frigate.api.auth import require_role
@@ -130,7 +130,14 @@ def metrics(request: Request):
     """Expose Prometheus metrics endpoint and update metrics with latest stats"""
     # Retrieve the latest statistics and update the Prometheus metrics
     stats = request.app.stats_emitter.get_latest_stats()
-    update_metrics(stats)
+    # query DB for count of events by camera, label
+    event_counts: List[Dict[str, Any]] = (
+        Event.select(Event.camera, Event.label, fn.Count())
+        .group_by(Event.camera, Event.label)
+        .dicts()
+    )
+
+    update_metrics(stats=stats, event_counts=event_counts)
     content, content_type = get_metrics()
     return Response(content=content, media_type=content_type)