extends Node
## Background music that carries on across scene changes. Scenes ask for a track; the
## player crossfades to it, or keeps playing if it is already on.

## Loaded on first use rather than preloaded, so this autoload never depends on the
## music having been imported yet. Looping is set in each track's .import file.
const TRACKS := {
	menu = "res://assets/music/menu.ogg",
	game = "res://assets/music/game.ogg",
}
const VOLUME_DB := { menu = -6.0, game = -10.0 }
const FADE_SECONDS := 0.8
const SILENT_DB := -40.0

var _player := AudioStreamPlayer.new()
var _track := ""


func _ready() -> void:
	process_mode = Node.PROCESS_MODE_ALWAYS
	add_child(_player)


func play(track: String) -> void:
	if track == _track and _player.playing:
		return
	_track = track
	if not Progress.music_on():
		return
	var tween := create_tween()
	if _player.playing:
		tween.tween_property(_player, "volume_db", SILENT_DB, FADE_SECONDS / 2.0)
	tween.tween_callback(_start.bind(track))
	tween.tween_property(_player, "volume_db", VOLUME_DB[track], FADE_SECONDS / 2.0)


func set_enabled(on: bool) -> void:
	Progress.set_music_on(on)
	if on:
		var track := _track
		_track = ""
		play(track if track != "" else "menu")
	else:
		_player.stop()


func _start(track: String) -> void:
	_player.stream = load(TRACKS[track])
	_player.volume_db = SILENT_DB
	_player.play()