from __future__ import annotations

from pathlib import Path

try:
    import fcntl
except ImportError:  # pragma: no cover - exercised by Windows validation
    fcntl = None
    import msvcrt


class MaintenanceLock:
    """Process fence used only by fixture and later approved activation executors."""

    def __init__(self, path: Path) -> None:
        self.path = path
        self._handle = None

    def __enter__(self) -> "MaintenanceLock":
        self.path.parent.mkdir(parents=True, exist_ok=True)
        self._handle = self.path.open("a+")
        if fcntl is not None:
            try:
                fcntl.flock(self._handle.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
            except BlockingIOError:
                self._handle.close()
                self._handle = None
                raise
        else:
            self._handle.seek(0)
            try:
                msvcrt.locking(self._handle.fileno(), msvcrt.LK_NBLCK, 1)
            except OSError as exc:
                self._handle.close()
                self._handle = None
                raise BlockingIOError("maintenance lock held") from exc
        return self

    def __exit__(self, exc_type, exc, tb) -> None:
        if self._handle is not None:
            if fcntl is not None:
                fcntl.flock(self._handle.fileno(), fcntl.LOCK_UN)
            else:
                self._handle.seek(0)
                msvcrt.locking(self._handle.fileno(), msvcrt.LK_UNLCK, 1)
            self._handle.close()
            self._handle = None