App\services\Media::tidy PHP Method

    public function tidy()
    {
        $inUseAlbums = Song::select('album_id')->groupBy('album_id')->get()->pluck('album_id')->toArray();
        $inUseAlbums[] = Album::UNKNOWN_ID;
        Album::deleteWhereIDsNotIn($inUseAlbums);
        $inUseArtists = Album::select('artist_id')->groupBy('artist_id')->get()->pluck('artist_id')->toArray();
        $contributingArtists = Song::distinct()->select('contributing_artist_id')->groupBy('contributing_artist_id')->get()->pluck('contributing_artist_id')->toArray();
        $inUseArtists = array_merge($inUseArtists, $contributingArtists);
        $inUseArtists[] = Artist::UNKNOWN_ID;
        $inUseArtists[] = Artist::VARIOUS_ID;
        Artist::deleteWhereIDsNotIn(array_filter($inUseArtists));
    }