from bilibili_api import video, sync


def geturl(vn: str) -> str:
    """Get audio download URL from AV or BV number with bilibili-api-python.

    Parameters
    ----------
    vn : str
        AV or BV number.

    Returns
    -------
    str
        URL of audio stream.

    Raises
    ------
    InvalidVideoNumberException
        If the format of AV or BV video number is invalid.
    BiliBiliAPIException
        If bilibili-api-python raises exception.
    BadVideoException
        If video is in flv format.
    """

    class InvalidVideoNumberException(Exception):
        pass

    class BiliBiliAPIException(Exception):
        pass

    class BadVideoException(Exception):
        pass

    if len(vn) <= 2:
        raise InvalidVideoNumberException("Video number too short!")
    if vn[:2].upper() == "AV":
        if not vn[2:].isnumeric():
            raise InvalidVideoNumberException("Invalid AV video number!")
        else:
            v = video.Video(aid="AV" + vn[2:])
    if vn[:2].upper() != "BV":
        raise InvalidVideoNumberException("Invalid video number!")
    else:
        v = video.Video(bvid="BV" + vn[2:])

    try:
        download_url_data = sync(v.get_download_url(0))
        detecter = video.VideoDownloadURLDataDetecter(data=download_url_data)
        streams = detecter.detect_best_streams()
    except:
        raise BiliBiliAPIException("Error happens with bilibili-api-python.")
    if detecter.check_flv_stream() == True:
        raise BadVideoException("Video is only available in flv format.")

    return streams[1].url