import jsonfile
import youtube

MUSIC_FILE = "music.json"


def load_playlist() -> tuple[dict, list[str]]:
    data = jsonfile.load(MUSIC_FILE)
    return data, data.setdefault("videos", [])


def list_songs() -> list[str]:
    _, videos = load_playlist()
    return [youtube.video_id(video) or video for video in videos]


def find_index(videos: list[str], identifier: str) -> int | None:
    return next((index for index, video in enumerate(videos) if youtube.video_id(video) == identifier), None)


def add_song(text: str) -> str:
    identifier = youtube.video_id(text)
    if not identifier:
        raise ValueError(f"{text} is not a YouTube link or video ID")
    data, videos = load_playlist()
    if find_index(videos, identifier) is not None:
        raise ValueError(f"{identifier} is already in the playlist")
    videos.append(youtube.watch_url(identifier))
    jsonfile.save(MUSIC_FILE, data)
    return identifier


def remove_song(identifier: str) -> None:
    data, videos = load_playlist()
    index = find_index(videos, identifier)
    if index is None:
        raise ValueError(f"{identifier} is not in the playlist")
    videos.pop(index)
    jsonfile.save(MUSIC_FILE, data)


def move_song(identifier: str, step: int) -> None:
    data, videos = load_playlist()
    index = find_index(videos, identifier)
    if index is None:
        raise ValueError(f"{identifier} is not in the playlist")
    target = index + step
    if not 0 <= target < len(videos):
        return
    videos[index], videos[target] = videos[target], videos[index]
    jsonfile.save(MUSIC_FILE, data)