fix(alerts): expose alertmanager webhook request metrics

apps/api/tests/test_alertmanager_webhook_metrics.py

@@ -0,0 +1,77 @@
+from __future__ import annotations
+
+import pytest
+from fastapi import BackgroundTasks, HTTPException
+from prometheus_client import generate_latest
+from starlette.requests import Request
+
+from src.api.v1.webhooks import AlertmanagerPayload, alertmanager_webhook
+from src.core.metrics import WEBHOOK_REQUESTS_TOTAL
+
+
+def _request(
+    *,
+    client_host: str = "127.0.0.1",
+    headers: list[tuple[bytes, bytes]] | None = None,
+) -> Request:
+    return Request(
+        {
+            "type": "http",
+            "method": "POST",
+            "path": "/api/v1/webhooks/alertmanager",
+            "scheme": "http",
+            "server": ("testserver", 80),
+            "client": (client_host, 50000),
+            "query_string": b"",
+            "headers": headers or [],
+        }
+    )
+
+
+def _webhook_count(status: str) -> float:
+    return WEBHOOK_REQUESTS_TOTAL.labels(
+        source="alertmanager",
+        status=status,
+    )._value.get()
+
+
+def _metrics_text() -> str:
+    return generate_latest().decode("utf-8")
+
+
+@pytest.mark.asyncio
+async def test_alertmanager_no_firing_payload_records_success_metric() -> None:
+    before = _webhook_count("success")
+
+    response = await alertmanager_webhook(
+        _request(),
+        AlertmanagerPayload(status="resolved", alerts=[]),
+        BackgroundTasks(),
+    )
+
+    assert response.success is True
+    assert response.message == "No firing alerts to process"
+    assert _webhook_count("success") == before + 1
+    assert (
+        'awoooi_webhook_requests_total{source="alertmanager",status="success"}'
+        in _metrics_text()
+    )
+
+
+@pytest.mark.asyncio
+async def test_alertmanager_external_reject_records_error_metric() -> None:
+    before = _webhook_count("error")
+
+    with pytest.raises(HTTPException) as exc_info:
+        await alertmanager_webhook(
+            _request(client_host="8.8.8.8"),
+            AlertmanagerPayload(status="resolved", alerts=[]),
+            BackgroundTasks(),
+        )
+
+    assert exc_info.value.status_code == 403
+    assert _webhook_count("error") == before + 1
+    assert (
+        'awoooi_webhook_requests_total{source="alertmanager",status="error"}'
+        in _metrics_text()
+    )