"""
文件级并发控制 — 解决 V1 P0-4 零并发控制问题。
基于 fcntl.flock 的进程级文件锁，超时自动释放。
"""

from __future__ import annotations

import fcntl
import os
import time
from pathlib import Path


class FileLock:
    """基于 fcntl.flock(LOCK_EX | LOCK_NB) 的进程级文件锁"""

    def __init__(self, path: Path, timeout: float = 10.0):
        self._path = path.with_suffix(path.suffix + ".lock") if not path.suffix.endswith(".lock") else path
        self._timeout = timeout
        self._fd: int | None = None

    def __enter__(self) -> FileLock:
        self._fd = os.open(self._path, os.O_CREAT | os.O_RDWR)
        deadline = time.monotonic() + self._timeout
        while True:
            try:
                fcntl.flock(self._fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
                return self
            except OSError:
                if time.monotonic() >= deadline:
                    os.close(self._fd)
                    self._fd = None
                    raise TimeoutError(f"lock timeout after {self._timeout}s: {self._path}")
                time.sleep(0.1)

    def __exit__(self, *exc) -> None:
        if self._fd is not None:
            fcntl.flock(self._fd, fcntl.LOCK_UN)
            os.close(self._fd)
            self._fd = None

    @property
    def path(self) -> Path:
        return self._path