from __future__ import annotations

import os
import fcntl
from typing import Optional

_LOCK_FD: Optional[int] = None  # keep fd open for process lifetime


def should_start_scheduler() -> bool:
    """Return True in exactly one process (the scheduler owner).

    Under gunicorn --workers N, code is imported in N processes. If APScheduler
    starts at import time, you get N schedulers => N× API calls.

    We prevent that by taking a non-blocking exclusive lock on a lockfile.
    """
    global _LOCK_FD
    if _LOCK_FD is not None:
        return True

    lock_path = os.environ.get("LAIR_SCHED_LOCK", "/tmp/lair-scheduler.lock")
    fd = os.open(lock_path, os.O_CREAT | os.O_RDWR, 0o644)
    try:
        fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        _LOCK_FD = fd
        return True
    except BlockingIOError:
        os.close(fd)
        return False
    except Exception:
        try:
            os.close(fd)
        finally:
            return False