Implement move instruction generation

import re

from collections.abc import Sequence

from pathlib import Path

from karaokatalog.instructions.MoveInstruction import MoveInstruction

from karaokatalog.Song import Song

FORBIDDEN_CHARACTERS = re.compile(r'[/<>:"\\|?*]')

def _get_canonical_song_dir(song: Song, variant: int = 0) -> Path:

    """

    Get the (relative) canonical directory in which this song should be located, that is

    the directory f"{song.artist}/{song.title}".

    Illegal characters are replaced. If variant > 0, f" ({variant})" is appended to the result.

    """

    variant_suffix = f" ({variant})" if variant > 0 else ""

    return Path(FORBIDDEN_CHARACTERS.sub("", song.artist)) / Path(

        FORBIDDEN_CHARACTERS.sub("", song.title) + variant_suffix

    )

def move(songs: Sequence[Song], base_dir: Path) -> Sequence[MoveInstruction]:

    """

    Create move instructions to move every song into the proper song directory

    within the given base_dir.

    """

    raise NotImplementedError()  # TODO

    song_dirs = set(song.dir.relative_to(base_dir) for song in songs)

    move_instructions = []

    for song in songs:

        absolute_song_dir = song.dir

        song_dir = absolute_song_dir.relative_to(base_dir)

        canonical_song_dir = _get_canonical_song_dir(song)

        if song_dir not in song_dirs:

            # A move instruction has already been generated for the dir this song is in

            # (which is possible, because some dirs contain multiple (variants of) songs)

            continue

        if song_dir != canonical_song_dir:

            # song_dir is not a good name, we want to replace it, so this path will soon be free

            song_dirs.remove(song_dir)

            # Find a canonical song dir variant that does not yet exist

            variant = 1

            while canonical_song_dir in song_dirs:

                canonical_song_dir = _get_canonical_song_dir(song, variant)

            song_dirs.add(canonical_song_dir)

            move_instructions.append(

                MoveInstruction(absolute_song_dir, base_dir / canonical_song_dir)

            )

    return tuple(move_instructions)