rthythm_archor_game/scenes/audio/audio_layer_controller.gd

class_name AudioLayerController
extends Node

## Presentation-layer dual music loops (AnchorV1.0 chapter 20).
## Past and Future layers start together and stay in sync forever; a phase
## switch only crossfades volumes. The clock authority stays with
## RhythmManager — drift correction seeks THESE players, never the clock.
##
## Placeholder assets: both layers use the same song; the Future layer is
## routed through a low-pass bus so the switch is audible until a real
## Future loop asset lands (BPM/beat-aligned per the design doc).

const FUTURE_BUS_NAME := "TimePhaseFuture"
const MUSIC_BUS_NAME := "Music"

@export var past_stream: AudioStream
@export var future_stream: AudioStream
@export var default_stream_path := "res://assets/audio/ev_past1.mp3"
@export var crossfade_seconds := 0.35
@export var active_volume_db := 0.0
@export var inactive_volume_db := -60.0
@export var drift_check_interval := 2.0
@export var drift_threshold_seconds := 0.015
@export var mute_clock := true
@export var future_lowpass_cutoff_hz := 2200.0

var past_player: AudioStreamPlayer
var future_player: AudioStreamPlayer

var _fade_tween: Tween
var _drift_accum := 0.0


func _ready() -> void:
	if DisplayServer.get_name() == "headless":
		return
	if past_stream == null and ResourceLoader.exists(default_stream_path):
		past_stream = load(default_stream_path)
	if future_stream == null:
		future_stream = past_stream
	_ensure_future_bus()
	# 双音轨走 Music 总线（Future 层经 TimePhaseFuture 低通后 send 到 Music），
	# 与标题音乐一致，音乐音量设置才能同时约束标题与局内音乐。
	past_player = _make_layer_player("PastLoop", past_stream, MUSIC_BUS_NAME if AudioServer.get_bus_index(MUSIC_BUS_NAME) != -1 else "Master")
	future_player = _make_layer_player("FutureLoop", future_stream, FUTURE_BUS_NAME)
	var bus := _event_bus_or_null()
	if bus != null and bus.has_signal("time_phase_changed") and not bus.is_connected("time_phase_changed", _on_time_phase_changed):
		bus.connect("time_phase_changed", _on_time_phase_changed)
	_start_layers()
	_apply_phase_volumes(_current_time_phase(), true)
	if mute_clock:
		var rhythm := _rhythm_manager_or_null()
		if rhythm != null:
			rhythm.set("volume_db", -80.0)


func _process(delta: float) -> void:
	if past_player == null:
		return
	_drift_accum += delta
	if _drift_accum < drift_check_interval:
		return
	_drift_accum = 0.0
	_correct_layer_drift()


## Snaps both layers back onto the clock immediately (a fresh run just
## re-zeroed RhythmManager) instead of waiting for the next drift check.
func restart_layers() -> void:
	_start_layers()
	_apply_phase_volumes(_current_time_phase(), true)
	_drift_accum = 0.0


func _start_layers() -> void:
	var rhythm := _rhythm_manager_or_null()
	var start_position := 0.0
	if rhythm != null and rhythm.has_method("song_position"):
		start_position = maxf(0.0, float(rhythm.call("song_position")))
	for player: AudioStreamPlayer in [past_player, future_player]:
		if player != null and player.stream != null:
			player.play(start_position)


func _correct_layer_drift() -> void:
	var rhythm := _rhythm_manager_or_null()
	if rhythm == null or not rhythm.has_method("song_position"):
		return
	if not bool(rhythm.get("running")):
		return
	var target := float(rhythm.call("song_position"))
	for player: AudioStreamPlayer in [past_player, future_player]:
		if player == null or not player.playing or player.stream == null:
			continue
		var length := float(player.stream.get_length())
		var wrapped_target := fmod(target, length) if length > 0.0 else target
		var raw_drift := absf(player.get_playback_position() - wrapped_target)
		var drift := minf(raw_drift, length - raw_drift) if length > 0.0 else raw_drift
		if drift > drift_threshold_seconds:
			player.seek(wrapped_target)


func _on_time_phase_changed(_previous: StringName, current: StringName, _reason: StringName) -> void:
	_apply_phase_volumes(current, false)


func _apply_phase_volumes(time_phase: StringName, instant: bool) -> void:
	if past_player == null or future_player == null:
		return
	var past_target := active_volume_db if time_phase != &"future" else inactive_volume_db
	var future_target := active_volume_db if time_phase == &"future" else inactive_volume_db
	if _fade_tween != null and _fade_tween.is_valid():
		_fade_tween.kill()
	if instant:
		past_player.volume_db = past_target
		future_player.volume_db = future_target
		return
	_fade_tween = create_tween()
	_fade_tween.set_parallel(true)
	_fade_tween.tween_property(past_player, "volume_db", past_target, crossfade_seconds)
	_fade_tween.tween_property(future_player, "volume_db", future_target, crossfade_seconds)


func _make_layer_player(player_name: String, stream: AudioStream, bus_name: String) -> AudioStreamPlayer:
	var player := AudioStreamPlayer.new()
	player.name = player_name
	player.stream = stream
	player.volume_db = inactive_volume_db
	if AudioServer.get_bus_index(bus_name) != -1:
		player.bus = bus_name
	add_child(player)
	return player


func _ensure_future_bus() -> void:
	var existing := AudioServer.get_bus_index(FUTURE_BUS_NAME)
	if existing != -1:
		_route_bus_to_music(existing)
		return
	AudioServer.add_bus()
	var bus_index := AudioServer.bus_count - 1
	AudioServer.set_bus_name(bus_index, FUTURE_BUS_NAME)
	var lowpass := AudioEffectLowPassFilter.new()
	lowpass.cutoff_hz = future_lowpass_cutoff_hz
	AudioServer.add_bus_effect(bus_index, lowpass)
	_route_bus_to_music(bus_index)


func _route_bus_to_music(bus_index: int) -> void:
	if AudioServer.get_bus_index(MUSIC_BUS_NAME) != -1:
		AudioServer.set_bus_send(bus_index, MUSIC_BUS_NAME)


func _current_time_phase() -> StringName:
	var manager := get_tree().root.get_node_or_null("TimePhaseManager") if is_inside_tree() else null
	if manager != null:
		return StringName(str(manager.get("current_time_phase")))
	return &"past"


func _rhythm_manager_or_null() -> Node:
	if not is_inside_tree():
		return null
	return get_tree().root.get_node_or_null("RhythmManager")


func _event_bus_or_null() -> Node:
	if not is_inside_tree():
		return null
	return get_tree().root.get_node_or_null("EventBus")