"""
Startup dependency checks for DB and Redis.

Fail-fast checks used by long-running entrypoints (web/celery) to avoid
silent hangs on connection issues.
"""

from __future__ import annotations

import sys
from urllib.parse import urlparse

import psycopg2
import redis
from django.conf import settings


def _log(message: str) -> None:
    """Log to stderr to be visible early in startup."""
    print(message, file=sys.stderr)


def _check_db(timeout_seconds: int) -> tuple[bool, str]:
    db = settings.DATABASES["default"]
    params = {
        "dbname": db.get("NAME"),
        "user": db.get("USER"),
        "password": db.get("PASSWORD"),
        "host": db.get("HOST"),
        "port": db.get("PORT"),
        "connect_timeout": timeout_seconds,
    }

    options = db.get("OPTIONS", {})
    if options.get("sslmode"):
        params["sslmode"] = options["sslmode"]

    conn = None
    try:
        conn = psycopg2.connect(**params)
        with conn.cursor() as cursor:
            cursor.execute("SELECT 1")
            cursor.fetchone()
        return True, "OK"
    except Exception as exc:  # noqa: BLE001
        target = f"{params['host']}:{params['port']}/{params['dbname']}"
        return False, f"{target} ({exc})"
    finally:
        if conn is not None:
            conn.close()


def _check_redis(timeout_seconds: int) -> tuple[bool, str]:
    redis_url = settings.CACHES["default"]["LOCATION"]
    try:
        client = redis.Redis.from_url(
            redis_url,
            socket_connect_timeout=timeout_seconds,
            socket_timeout=timeout_seconds,
        )
        client.ping()
        return True, "OK"
    except Exception as exc:  # noqa: BLE001
        parsed = urlparse(redis_url)
        target = f"{parsed.hostname}:{parsed.port}{parsed.path or ''}"
        return False, f"{target} ({exc})"


def run_startup_checks(*, component: str = "app") -> None:
    """Run startup checks and exit process on failure."""
    if not getattr(settings, "STARTUP_CHECKS_ENABLED", True):
        return

    db_timeout = int(getattr(settings, "STARTUP_DB_TIMEOUT_SECONDS", 3))
    redis_timeout = int(getattr(settings, "STARTUP_REDIS_TIMEOUT_SECONDS", 3))

    db_ok, db_message = _check_db(db_timeout)
    if not db_ok:
        _log(
            f"[startup:{component}] DB check failed "
            f"(timeout={db_timeout}s): {db_message}"
        )
        raise SystemExit(1)

    redis_ok, redis_message = _check_redis(redis_timeout)
    if not redis_ok:
        _log(
            f"[startup:{component}] Redis check failed "
            f"(timeout={redis_timeout}s): {redis_message}"
        )
        raise SystemExit(1)