"""Crash-safe interprocess locking scoped by workspace and job type."""

from __future__ import annotations

import fcntl
import hashlib
import os
import re
from pathlib import Path
from types import TracebackType


class JobAlreadyRunningError(RuntimeError):
    pass


_JOB_KEY = re.compile(r"^[a-z][a-z0-9_-]{0,63}$")


def _lock_name(workspace_id: str, job_type: str) -> str:
    if not _JOB_KEY.fullmatch(workspace_id) or not _JOB_KEY.fullmatch(job_type):
        raise ValueError("lock identifiers must be lowercase filesystem-safe keys")
    workspace_key = hashlib.sha256(workspace_id.encode("utf-8")).hexdigest()[:16]
    return f"{workspace_key}-{job_type}.lock"


class WorkspaceJobLock:
    """Advisory kernel lock; the inode remains stable and is never deleted by PID."""

    def __init__(self, workspace_root: Path, workspace_id: str, job_type: str) -> None:
        self.path = workspace_root / ".tht-jobs" / ".locks" / _lock_name(
            workspace_id, job_type
        )
        self._fd: int | None = None

    def acquire(self) -> "WorkspaceJobLock":
        if self._fd is not None:
            raise RuntimeError("job lock is already held by this object")
        self.path.parent.mkdir(parents=True, exist_ok=True)
        fd = os.open(self.path, os.O_RDWR | os.O_CREAT, 0o600)
        try:
            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except BlockingIOError as error:
            os.close(fd)
            raise JobAlreadyRunningError("this workspace job is already running") from error
        self._fd = fd
        return self

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

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

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        exc: BaseException | None,
        traceback: TracebackType | None,
    ) -> None:
        self.release()