Add prune logic

import re

from collections.abc import Sequence

from karaokatalog.deduplicate.instructions.DeleteInstruction import DeleteInstruction

from karaokatalog.Song import Song

DISCOURAGED_DIR_PATTERN = re.compile(r"/UltrastarDX/Ultrastar DX/(Unsortiert/)?")

def prune(equivalent_songs: Sequence[Song]) -> Sequence[DeleteInstruction]:

    """

    Prune a sequence of equivalent songs, by returning a sequence of instructions

    that delete all but one song in this sequence.

    """

    pass

    preferred_songs = tuple(

        song

        for song in equivalent_songs

        if not DISCOURAGED_DIR_PATTERN.search(str(song.dir))

    )

    discouraged_songs = tuple(

        song

        for song in equivalent_songs

        if DISCOURAGED_DIR_PATTERN.search(str(song.dir))

    )

    # Keep an arbitrarily chosen preferred song, if there is at least one, otherwise, just keep an arbitrarily chosen

    # discouraged song.

    song_to_keep = preferred_songs[0] if preferred_songs else discouraged_songs[0]

    return tuple(

        DeleteInstruction(song.dir)

        for song in equivalent_songs

        if song is not song_to_keep

    )