from __future__ import annotations

import hmac

from fastapi import APIRouter, Header, HTTPException
from fastapi.responses import Response
from prometheus_client import CONTENT_TYPE_LATEST, generate_latest
from sqlalchemy import func, select

from app.core.config import get_settings
from app.core.db import SessionLocal
from app.core.observability import OUTBOX_EVENTS
from app.models.outbox import DELIVERY_STATUSES, DEMO_SCENARIO_ERROR_CODE, OutboxEvent

router = APIRouter(tags=["observability"])
settings = get_settings()


def _refresh_database_metrics() -> None:
    with SessionLocal() as db:
        rows = db.execute(
            select(
                OutboxEvent.delivery_status,
                (OutboxEvent.last_error_code == DEMO_SCENARIO_ERROR_CODE).label("demo"),
                func.count(),
            ).group_by(OutboxEvent.delivery_status, "demo")
        ).all()
    OUTBOX_EVENTS.clear()
    # Keep every time series present even when a state currently contains no rows.
    # Stable zero-valued series make dashboards and alerts deterministic after resets,
    # restores and fresh installations instead of turning "zero" into "no data".
    for scenario in ("synthetic", "operational"):
        for status in DELIVERY_STATUSES:
            OUTBOX_EVENTS.labels(scenario, status).set(0)
    for status, is_demo, count in rows:
        OUTBOX_EVENTS.labels("synthetic" if is_demo else "operational", str(status)).set(count)


@router.get("/metrics", include_in_schema=False)
def metrics(authorization: str | None = Header(default=None)) -> Response:
    if settings.metrics_bearer_token:
        supplied = authorization.removeprefix("Bearer ") if authorization else ""
        if not hmac.compare_digest(supplied, settings.metrics_bearer_token):
            raise HTTPException(status_code=401, detail="Metrics token required")
    _refresh_database_metrics()
    return Response(content=generate_latest(), media_type=CONTENT_TYPE_LATEST)