"""Exclusive process ownership for the client state database."""

from __future__ import annotations

import fcntl
import os
from pathlib import Path
from typing import IO


class DatabaseLockedError(RuntimeError):
    pass


class DatabaseLease:
    def __init__(self, database: Path):
        self.path = Path(f"{database}.lock")
        self._file: IO[str] | None = None

    def acquire(self) -> None:
        if self._file is not None:
            return
        self.path.parent.mkdir(parents=True, exist_ok=True)
        lock_file = self.path.open("a+", encoding="utf-8")
        os.chmod(self.path, 0o600)
        try:
            fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
        except BlockingIOError as exc:
            lock_file.close()
            raise DatabaseLockedError(
                "client database is owned by a running process"
            ) from exc
        self._file = lock_file

    def release(self) -> None:
        if self._file is None:
            return
        try:
            fcntl.flock(self._file.fileno(), fcntl.LOCK_UN)
        finally:
            self._file.close()
            self._file = None

    def __enter__(self) -> "DatabaseLease":
        self.acquire()
        return self

    def __exit__(self, *_: object) -> None:
        self.release()