From ca8287cd8bd6614e867508c3a197ecc35991a891 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Luk=C3=A1=C5=A1=20Trkan?= <lukas@trkan.cz>
Date: Sun, 9 Nov 2025 12:43:27 +0100
Subject: [PATCH] feat(prometheus): add custom metrics

---
 7project/backend/app/app.py                 |  5 +++
 7project/backend/app/services/prometheus.py | 48 +++++++++++++++++++++
 7project/meetings/2025-10-30-meeting.md     |  4 +-
 3 files changed, 55 insertions(+), 2 deletions(-)
 create mode 100644 7project/backend/app/services/prometheus.py

diff --git a/7project/backend/app/app.py b/7project/backend/app/app.py
index 98b2c66..6bb0e5d 100644
--- a/7project/backend/app/app.py
+++ b/7project/backend/app/app.py
@@ -9,6 +9,8 @@ from fastapi.middleware.cors import CORSMiddleware
 from prometheus_fastapi_instrumentator import Instrumentator, metrics
 from starlette.requests import Request
 
+from app.services.prometheus import number_of_users, number_of_transactions
+
 from app.services import bank_scraper
 from app.workers.celery_tasks import load_transactions, load_all_transactions
 from app.models.user import User, OAuthAccount
@@ -50,6 +52,9 @@ fastApi.add_middleware(
 
 prometheus = Instrumentator().instrument(fastApi)
 
+# Register custom metrics
+prometheus.add(number_of_users()).add(number_of_transactions())
+
 prometheus.expose(
     fastApi,
     endpoint="/metrics",
diff --git a/7project/backend/app/services/prometheus.py b/7project/backend/app/services/prometheus.py
new file mode 100644
index 0000000..0f9380a
--- /dev/null
+++ b/7project/backend/app/services/prometheus.py
@@ -0,0 +1,48 @@
+from typing import Callable
+from prometheus_fastapi_instrumentator.metrics import Info
+from prometheus_client import Gauge
+from sqlalchemy import select, func
+
+from app.core.db import async_session_maker
+from app.models.transaction import Transaction
+from app.models.user import User
+
+
+def number_of_users() -> Callable[[Info], None]:
+    METRIC = Gauge(
+        "number_of_users_total",
+        "Number of registered users.",
+        labelnames=("users",)
+    )
+
+    async def instrumentation(info: Info) -> None:
+        try:
+            async with async_session_maker() as session:
+                result = await session.execute(select(func.count(User.id)))
+                user_count = result.scalar_one() or 0
+        except Exception:
+            # In case of DB errors, avoid crashing metrics endpoint
+            user_count = 0
+        METRIC.labels(users="total").set(user_count)
+
+    return instrumentation
+
+
+def number_of_transactions() -> Callable[[Info], None]:
+    METRIC = Gauge(
+        "number_of_transactions_total",
+        "Number of transactions stored.",
+        labelnames=("transactions",)
+    )
+
+    async def instrumentation(info: Info) -> None:
+        try:
+            async with async_session_maker() as session:
+                result = await session.execute(select(func.count()).select_from(Transaction))
+                transaction_count = result.scalar_one() or 0
+        except Exception:
+            # In case of DB errors, avoid crashing metrics endpoint
+            transaction_count = 0
+        METRIC.labels(transactions="total").set(transaction_count)
+
+    return instrumentation
diff --git a/7project/meetings/2025-10-30-meeting.md b/7project/meetings/2025-10-30-meeting.md
index aa3c380..503b366 100644
--- a/7project/meetings/2025-10-30-meeting.md
+++ b/7project/meetings/2025-10-30-meeting.md
@@ -43,8 +43,8 @@ The tracker should not store the transactions in the database - security vulnera
 
 Last 3 minutes of the meeting, summarize action items.
 
-- [ ] Change the name on frontend from 7project
-- [ ] Finalize the funcionality and everyting in the code part
+- [x] Change the name on frontend from 7project
+- [x] Finalize the funcionality and everyting in the code part
 - [ ] Try to finalize report with focus on reproducibility
 - [ ] More high level explanation of the workflow in the report