Add Clear cache to the settings

A new row, "Downloaded pictures and songs", shows how much space the cached
character pictures, covers and downloaded songs take, with a Clear cache
button. Clearing deletes them, but keeps the songs the current quiz uses,
the settings, config.ini and the saved quiz. The characters are loaded
again at once; covers come back when they are shown.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

popups/SettingsPopup.tscn

@@ -253,6 +253,27 @@ layout_mode = 2
 focus_mode = 0
 text = "Open folder"
 
+[node name="ClearCacheRow" type="HBoxContainer" parent="SettingsPanel/VBoxContainer"]
+layout_mode = 2
+
+[node name="Title" type="Label" parent="SettingsPanel/VBoxContainer/ClearCacheRow"]
+layout_mode = 2
+size_flags_horizontal = 3
+theme_type_variation = &"SettingsRowLabel"
+text = "Downloaded pictures and songs"
+
+[node name="CacheSizeLabel" type="Label" parent="SettingsPanel/VBoxContainer/ClearCacheRow"]
+unique_name_in_owner = true
+layout_mode = 2
+
+[node name="ClearCacheButton" type="Button" parent="SettingsPanel/VBoxContainer/ClearCacheRow"]
+unique_name_in_owner = true
+layout_mode = 2
+tooltip_text = "Deletes the downloaded character pictures, covers and songs.
+They are downloaded again when needed. Songs in the current quiz are kept."
+focus_mode = 0
+text = "Clear cache"
+
 [node name="FolderDialog" type="FileDialog" parent="."]
 unique_name_in_owner = true
 title = "Choose a music folder"

popups/settings_popup.gd

@@ -18,6 +18,8 @@ signal server_changed
 
 ## Emitted when a folder of characters is picked or Use server is pressed for them.
 signal characters_changed
+## Emitted when Clear cache is pressed, for the caches to delete their files.
+signal clear_cache_requested
 
 ## Space between the rows and the panel's edges.
 const PADDING: Vector2 = Vector2(20, 12)
@@ -46,6 +48,8 @@ const PADDING: Vector2 = Vector2(20, 12)
 @onready var characters_error_label: Label = %CharactersErrorLabel
 @onready var character_folder_dialog: FileDialog = %CharacterFolderDialog
 @onready var open_config_folder_button: Button = %OpenConfigFolderButton
+@onready var cache_size_label: Label = %CacheSizeLabel
+@onready var clear_cache_button: Button = %ClearCacheButton
 
 ## Shows a folder in the system's file manager. The tests replace it, so no file manager
 ## opens while they run.
@@ -77,6 +81,7 @@ func _ready() -> void:
 	use_server_characters_button.pressed.connect(use_server_characters)
 	open_config_folder_button.pressed.connect(open_config_folder)
 	open_config_folder_button.tooltip_text = Settings.config_dir()
+	clear_cache_button.pressed.connect(clear_cache)
 	play_order_button.item_selected.connect(_on_play_order_selected)
 	lower_cache_button.pressed.connect(lower_cache)
 	increase_cache_button.pressed.connect(increase_cache)
@@ -136,6 +141,40 @@ func open_config_folder() -> void:
 	show_folder.call(dir)
 
 
+## Deletes the downloaded character pictures, covers and songs, except the songs the
+## quiz uses, and shows how much space that freed.
+func clear_cache() -> void:
+	var freed: int = cache_size()
+	clear_cache_requested.emit()
+	Playlist.clear_song_files(Playlist.song_files_in_use())
+	cache_size_label.text = "Cleared " + size_text(freed)
+	clear_cache_button.disabled = true
+
+
+## Shows how much space the downloaded files take.
+func show_cache_size() -> void:
+	var size: int = cache_size()
+	cache_size_label.text = size_text(size)
+	clear_cache_button.disabled = size == 0
+
+
+## How many bytes the downloaded character pictures, covers and songs take, leaving out
+## the songs the quiz uses, which clearing keeps.
+static func cache_size() -> int:
+	return FileCache.folder_size(CharacterCache.folder()) \
+			+ FileCache.folder_size(CoverCache.folder()) \
+			+ FileCache.folder_size(Playlist.songs_folder(), Playlist.song_files_in_use())
+
+
+## [param bytes] for people, e.g. "350 KB" or "14.2 MB".
+static func size_text(bytes: int) -> String:
+	if bytes == 0:
+		return "Nothing"
+	if bytes < 1 << 20:
+		return "%d KB" % ceili(bytes / 1024.0)
+	return "%.1f MB" % (bytes / float(1 << 20))
+
+
 ## Reads the characters from the folder at [param path] instead of the server. A folder
 ## without pictures is not used, and the popup says so.
 func use_character_folder(path: String) -> void:
@@ -189,6 +228,7 @@ func _use_server(new_server: int) -> void:
 func _on_visibility_changed() -> void:
 	if visible:
 		_update_fullscreen_button()
+		show_cache_size()
 		random_mode_button.select(Settings.random_mode)
 		add_to_database_button.set_pressed_no_signal(Settings.add_to_stats)
 	else: