import os
from typing import IO, Any
from urllib.parse import parse_qs, urlparse

if os.name == "nt":
    import msvcrt
elif os.name == "posix":
    import fcntl


class FileLock:
    @staticmethod
    def lock(file: IO[Any]) -> None:
        if os.name == "nt":
            msvcrt.locking(file.fileno(), msvcrt.LK_LOCK, 1)
        elif os.name == "posix":
            fcntl.flock(file.fileno(), fcntl.LOCK_EX)

    @staticmethod
    def unlock(file: IO[Any]) -> None:
        if os.name == "nt":
            msvcrt.locking(file.fileno(), msvcrt.LK_UNLCK, 1)
        elif os.name == "posix":
            fcntl.flock(file.fileno(), fcntl.LOCK_UN)


def page_num_from_url(url: str) -> int | None:
    parsed_url = urlparse(url)
    params = parse_qs(parsed_url.query)
    page = params.get("page", [None])[0]
    return int(page) if page is not None else None