"""Shared writer leases and exclusive GC on the common data volume."""
import asyncio
import os
from contextlib import asynccontextmanager

from app.config import get_settings


def acquire(exclusive=False):
    root = get_settings().data_dir
    root.mkdir(parents=True, exist_ok=True)
    handle = (root / "maintenance.lock").open("a+b")
    try:
        if os.name == "nt":
            import msvcrt
            if handle.tell() == 0:
                handle.write(b"0")
                handle.flush()
            handle.seek(0)
            msvcrt.locking(handle.fileno(), msvcrt.LK_LOCK, 1)
        else:
            import fcntl
            fcntl.flock(handle, fcntl.LOCK_EX if exclusive else fcntl.LOCK_SH)
        return handle
    except BaseException:
        handle.close()
        raise


def release(handle):
    if os.name == "nt":
        import msvcrt
        handle.seek(0)
        msvcrt.locking(handle.fileno(), msvcrt.LK_UNLCK, 1)
    handle.close()


@asynccontextmanager
async def storage_access(exclusive=False):
    task = asyncio.create_task(asyncio.to_thread(acquire, exclusive))
    try:
        handle = await asyncio.shield(task)
    except asyncio.CancelledError:
        task.add_done_callback(lambda done: release(done.result()) if not done.cancelled() and not done.exception() else None)
        raise
    try:
        yield
    finally:
        release(handle)