Add offline mode: play from a music folder instead of the server

Settings has a Music folder row. A folder with subfolders is played as
soundtracks: Next picks a random subfolder and a random song in it, the
subfolder is the answer's soundtrack and the file name without its type the
song. The inspiration list and Search show the subfolders.

A folder with songs and no subfolders is a prepared quiz, played once in order
(natural sort) or at random, showing only the song title. It has no winning
score: after the last song Next becomes Show winner, and the players with the
most points win, ties included.

While a folder is used nothing but the characters is asked from the server:
Sync, QR, Statistics, the update check and play counting are off. Characters
fall back to the cached pictures when the server can't be reached. mp3, ogg and
wav play; other files and broken ones are skipped.

The old local playback code, the hidden Open button and the hidden Local toggle
are removed. Next now waits for the song to start before preparing the next one.

tests/unit/test_audio_file.gd

@@ -0,0 +1,45 @@
+extends GdUnitTestSuite
+## Reading songs from files by their type.
+
+
+@warning_ignore("unused_parameter")
+func test_playable_types_load(
+		file_name: String,
+		type: GDScript,
+		test_parameters: Array = [
+			["short.mp3", AudioStreamMP3], ["short.ogg", AudioStreamOggVorbis],
+			["short.wav", AudioStreamWAV],
+		],
+) -> void:
+	var stream: AudioStream = AudioFile.load("res://tests/data/" + file_name)
+
+	assert_object(stream).is_not_null()
+	assert_bool(is_instance_of(stream, type)).is_true()
+	assert_float(stream.get_length()).is_greater(0.0)
+
+
+func test_missing_file_gives_null() -> void:
+	assert_object(AudioFile.load("res://tests/data/missing.mp3")).is_null()
+
+
+func test_other_types_give_null() -> void:
+	var path: String = create_temp_dir("audio_file").path_join("song.flac")
+	FileAccess.open(path, FileAccess.WRITE).store_buffer(
+			FileAccess.get_file_as_bytes("res://tests/data/short.mp3"))
+
+	assert_object(AudioFile.load(path)).is_null()
+
+
+func test_broken_file_gives_null() -> void:
+	var path: String = create_temp_dir("audio_file").path_join("broken.mp3")
+	FileAccess.open(path, FileAccess.WRITE).store_string("not a song")
+
+	assert_object(AudioFile.load(path)).is_null()
+
+
+func test_playable_types() -> void:
+	assert_bool(AudioFile.is_playable("a/b/Song.MP3")).is_true()
+	assert_bool(AudioFile.is_playable("Song.ogg")).is_true()
+	assert_bool(AudioFile.is_playable("Song.wav")).is_true()
+	assert_bool(AudioFile.is_playable("Song.flac")).is_false()
+	assert_bool(AudioFile.is_playable("cover.jpg")).is_false()

tests/unit/test_audio_file.gd.uid

@@ -0,0 +1 @@
+uid://crghfr0gnyngh

tests/unit/test_character_cache.gd

@@ -189,3 +189,26 @@ func test_broken_index_starts_over() -> void:
 
 	assert_int(images.size()).is_equal(1)
 	assert_int(_server.count(_image_path("Crono.png"))).is_equal(2)
+
+
+func test_cached_pictures_are_shown_when_the_server_cannot_be_reached() -> void:
+	_serve({"Crono.png": 100, "Marle.png": 200})
+	_load_all()
+	_server.respond_json("/character/details", {}, 503)
+	_server.respond_json("/character/list", {}, 503)
+
+	var images: Array[Image] = _load_all()
+
+	assert_int(images.size()).is_equal(2)
+	assert_int(_server.count(_image_path("Crono.png"))).is_equal(1)
+	assert_bool(FileAccess.file_exists(CharacterCache.folder().path_join("Marle.png"))).is_true()
+
+
+func test_nothing_is_shown_without_a_server_or_cached_pictures() -> void:
+	var cache: CharacterCache = CharacterCache.new()
+	var listed: Array = []
+
+	cache.load_list(func(names: Array[String]) -> void: listed.append(names))
+
+	assert_array(listed).has_size(1)
+	assert_array(listed[0]).is_empty()

tests/unit/test_music_folder.gd

@@ -0,0 +1,202 @@
+extends GdUnitTestSuite
+## Music folders: soundtrack folders, where songs are picked at random from subfolders,
+## and prepared quizzes, where every song in the folder plays once.
+
+var _root: String
+var _mp3: PackedByteArray
+
+
+func before_test() -> void:
+	_root = create_temp_dir("music_folder_%d" % randi())
+	_mp3 = FileAccess.get_file_as_bytes("res://tests/data/short.mp3")
+
+
+func _song(relative_path: String) -> void:
+	_file(relative_path, _mp3)
+
+
+func _file(relative_path: String, bytes: PackedByteArray) -> void:
+	var path: String = _root.path_join(relative_path)
+	DirAccess.make_dir_recursive_absolute(path.get_base_dir())
+	FileAccess.open(path, FileAccess.WRITE).store_buffer(bytes)
+
+
+func _folder(relative_path: String = "") -> MusicFolder:
+	return MusicFolder.scan(_root.path_join(relative_path))
+
+
+func test_folder_with_subfolders_is_a_soundtrack_folder() -> void:
+	_song("Chrono Trigger/Corridors of Time.mp3")
+	_song("Final Fantasy VI/Dancing Mad.mp3")
+
+	var folder: MusicFolder = _folder()
+
+	assert_int(folder.kind).is_equal(MusicFolder.Kind.SOUNDTRACKS)
+	assert_array(folder.soundtrack_names()) \
+			.contains_exactly(["Chrono Trigger", "Final Fantasy VI"])
+
+
+func test_songs_at_the_top_of_a_soundtrack_folder_are_left_out() -> void:
+	_song("Chrono Trigger/Corridors of Time.mp3")
+	_song("Loose song.mp3")
+
+	var folder: MusicFolder = _folder()
+
+	for i: int in 10:
+		assert_str(folder.next_song().soundtrack_title).is_equal("Chrono Trigger")
+
+
+func test_folder_with_only_songs_is_a_prepared_quiz() -> void:
+	_song("01. Opening.mp3")
+	_song("02. Ace Combat 7 - Daredevil.mp3")
+
+	var folder: MusicFolder = _folder()
+
+	assert_int(folder.kind).is_equal(MusicFolder.Kind.PREPARED_QUIZ)
+	assert_int(folder.quiz_size()).is_equal(2)
+	assert_array(folder.soundtrack_names()).is_empty()
+
+
+func test_folder_without_songs_is_empty() -> void:
+	_file("notes.txt", "hello".to_utf8_buffer())
+	_file("Chrono Trigger/cover.jpg", "jpg".to_utf8_buffer())
+
+	assert_int(_folder().kind).is_equal(MusicFolder.Kind.EMPTY)
+
+
+func test_missing_folder_is_empty() -> void:
+	assert_int(_folder("missing").kind).is_equal(MusicFolder.Kind.EMPTY)
+
+
+func test_hidden_folders_and_files_are_left_out() -> void:
+	_song(".sync/Archive/Old.mp3")
+	_song("Chrono Trigger/.hidden.mp3")
+	_song("Chrono Trigger/Corridors of Time.mp3")
+
+	var folder: MusicFolder = _folder()
+
+	assert_array(folder.soundtrack_names()).contains_exactly(["Chrono Trigger"])
+	for i: int in 10:
+		assert_str(folder.next_song().song_title).is_equal("Corridors of Time")
+
+
+func test_hidden_folder_alone_does_not_make_a_soundtrack_folder() -> void:
+	_song(".sync/Archive/Old.mp3")
+	_song("01. Opening.mp3")
+
+	assert_int(_folder().kind).is_equal(MusicFolder.Kind.PREPARED_QUIZ)
+
+
+func test_songs_in_deeper_folders_belong_to_their_soundtrack() -> void:
+	_song("Xenogears/Disc 2/Small Two of Pieces.mp3")
+
+	var song: SongObject = _folder().next_song()
+
+	assert_str(song.soundtrack_title).is_equal("Xenogears")
+	assert_str(song.song_title).is_equal("Small Two of Pieces")
+
+
+func test_picked_song_has_its_file_and_names_without_the_file_type() -> void:
+	_song("Chrono Trigger/Corridors of Time.mp3")
+
+	var song: SongObject = _folder().next_song()
+
+	assert_str(song.song_path).is_equal(_root.path_join("Chrono Trigger/Corridors of Time.mp3"))
+	assert_str(song.soundtrack_title).is_equal("Chrono Trigger")
+	assert_str(song.song_title).is_equal("Corridors of Time")
+
+
+func test_soundtrack_folder_can_play_a_song_again() -> void:
+	_song("Chrono Trigger/Corridors of Time.mp3")
+	var folder: MusicFolder = _folder()
+
+	for i: int in 3:
+		assert_object(folder.next_song()).is_not_null()
+
+
+func test_files_that_cannot_be_played_are_skipped() -> void:
+	_song("Chrono Trigger/Corridors of Time.mp3")
+	_file("Chrono Trigger/Lost.flac", _mp3)
+	_file("Chrono Trigger/Broken.mp3", "not a song".to_utf8_buffer())
+	_file("Chrono Trigger/cover.jpg", "jpg".to_utf8_buffer())
+	var folder: MusicFolder = _folder()
+
+	for i: int in 10:
+		assert_str(folder.next_song().song_title).is_equal("Corridors of Time")
+
+
+func test_soundtrack_with_only_unplayable_files_is_left_out() -> void:
+	_song("Chrono Trigger/Corridors of Time.mp3")
+	_file("Tunic/Subterra.flac", _mp3)
+
+	assert_array(_folder().soundtrack_names()).contains_exactly(["Chrono Trigger"])
+
+
+func test_prepared_quiz_plays_in_natural_order_and_then_stops() -> void:
+	for file_name: String in ["10. Ten.mp3", "2. Two.mp3", "01. Warhammer.mp3",
+			"01. Opening.mp3"]:
+		_song(file_name)
+	var folder: MusicFolder = _folder()
+
+	var titles: Array[String] = []
+	for i: int in 4:
+		titles.append(folder.next_song().song_title)
+
+	assert_array(titles).contains_exactly(["01. Opening", "01. Warhammer", "2. Two", "10. Ten"])
+	assert_object(folder.next_song()).is_null()
+
+
+func test_prepared_quiz_has_no_soundtrack() -> void:
+	_song("04. Ace Combat 7 - Daredevil.mp3")
+
+	var song: SongObject = _folder().next_song()
+
+	assert_str(song.soundtrack_title).is_empty()
+	assert_str(song.song_title).is_equal("04. Ace Combat 7 - Daredevil")
+
+
+func test_random_prepared_quiz_plays_every_song_once() -> void:
+	for i: int in 8:
+		_song("%02d. Song.mp3" % i)
+	var folder: MusicFolder = _folder()
+	folder.set_play_order(MusicFolder.PlayOrder.RANDOM)
+
+	var titles: Array[String] = []
+	for i: int in 8:
+		titles.append(folder.next_song().song_title)
+
+	assert_array(titles).has_size(8)
+	for i: int in 8:
+		assert_array(titles).contains(["%02d. Song" % i])
+	assert_object(folder.next_song()).is_null()
+
+
+func test_restart_plays_the_prepared_quiz_from_the_start() -> void:
+	_song("01. One.mp3")
+	_song("02. Two.mp3")
+	var folder: MusicFolder = _folder()
+	folder.next_song()
+	folder.next_song()
+
+	folder.restart()
+
+	assert_str(folder.next_song().song_title).is_equal("01. One")
+
+
+func test_unplayable_file_in_a_prepared_quiz_is_skipped() -> void:
+	_song("01. One.mp3")
+	_file("02. Broken.mp3", "not a song".to_utf8_buffer())
+	_song("03. Three.mp3")
+	var folder: MusicFolder = _folder()
+
+	assert_str(folder.next_song().song_title).is_equal("01. One")
+	assert_str(folder.next_song().song_title).is_equal("03. Three")
+	assert_object(folder.next_song()).is_null()
+
+
+func test_display_name_is_the_folder_name() -> void:
+	_song("Musiktävling 2025/01. Opening.mp3")
+
+	var folder: MusicFolder = _folder("Musiktävling 2025/")
+
+	assert_str(folder.display_name()).is_equal("Musiktävling 2025")

tests/unit/test_music_folder.gd.uid

@@ -0,0 +1 @@
+uid://ca61kypdrbj8j