"""Cross-process locks for launcher-prefix mutations."""

from __future__ import annotations

from contextlib import contextmanager
from datetime import datetime
import fcntl
import os
from pathlib import Path
from typing import Iterator


class OperationBusyError(RuntimeError):
	"""Raised when another launcher-prefix operation is still active."""


@contextmanager
def launcher_operation_lock(lock_path: Path, operation: str) -> Iterator[None]:
	lock_path.parent.mkdir(parents=True, exist_ok=True)
	with lock_path.open("a+", encoding="utf-8") as handle:
		try:
			fcntl.flock(handle.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
		except BlockingIOError as exc:
			handle.seek(0)
			owner = handle.read().strip() or "unknown operation"
			raise OperationBusyError(
				f"launcher files are busy ({owner}); wait for it to finish and try again"
			) from exc
		handle.seek(0)
		handle.truncate()
		handle.write(
			f"{operation}, pid={os.getpid()}, "
			f"started={datetime.now().astimezone().isoformat()}\n"
		)
		handle.flush()
		try:
			yield
		finally:
			handle.seek(0)
			handle.truncate()
			handle.flush()
			fcntl.flock(handle.fileno(), fcntl.LOCK_UN)