"""One machine-wide lock for processes that consume the recording inbox."""
from __future__ import annotations

import fcntl
import os
from pathlib import Path


def acquire_recording_lock(path: Path):
    """Return an open file holding an exclusive lock, or exit if another consumer has it.

    The handle must stay referenced for the life of the process.
    """
    path.parent.mkdir(parents=True, exist_ok=True)
    handle = path.open("a+")
    try:
        fcntl.flock(handle, fcntl.LOCK_EX | fcntl.LOCK_NB)
    except OSError:
        handle.close()
        raise SystemExit(f"another recording consumer holds {path}")
    handle.seek(0)
    handle.truncate()
    handle.write(str(os.getpid()))
    handle.flush()
    return handle