# AppLifecycle (F5) —— 移动端应用生命周期集中处理。
#
# 把 SceneTree 转发来的 MainLoop 通知收成信号，并做默认动作：后台时暂停游戏
# 逻辑 / 降帧 / 停 BGM，恢复时还原；iOS 内存告警时广播让各缓存自清。渲染上下文
# 丢失（Android Vulkan surface）由 Godot 自己重建，我们持有的 GPU 资源都由
# RenderingServer 托管，无需干预。
#
# 用法：
#   var life := preload("res://app_lifecycle.gd").new()
#   add_child(life)                       # 越早越好（autoload 亦可）
#   life.bind(m2client, audio)            # 可选：自动接常见消费方
#   life.paused.connect(_on_bg); life.resumed.connect(_on_fg)
extends Node

signal paused                      # 进入后台（NOTIFICATION_APPLICATION_PAUSED）
signal resumed                     # 回到前台
signal focus_changed(focused: bool)
signal memory_warning             # iOS 内存压力
signal back_requested             # Android 返回键
signal close_requested            # 窗口关闭请求（桌面）

## 后台时是否 get_tree().paused = true（默认开；纯观战/录像可关）
var pause_tree_on_background := true
## 后台时把 max_fps 压到这个值省电（0 = 不改）
var background_max_fps := 8

var _bound_client: Node
var _bound_audio: Node
var _saved_max_fps := 0
var _bg := false

func _ready() -> void:
	# 通知在暂停树时也要能收到
	process_mode = Node.PROCESS_MODE_ALWAYS

func bind(m2client: Node = null, audio: Node = null) -> void:
	_bound_client = m2client
	_bound_audio = audio

func is_backgrounded() -> bool:
	return _bg

func _notification(what: int) -> void:
	match what:
		NOTIFICATION_APPLICATION_PAUSED:
			_enter_background()
		NOTIFICATION_APPLICATION_RESUMED:
			_exit_background()
		NOTIFICATION_APPLICATION_FOCUS_IN, NOTIFICATION_WM_WINDOW_FOCUS_IN:
			focus_changed.emit(true)
		NOTIFICATION_APPLICATION_FOCUS_OUT, NOTIFICATION_WM_WINDOW_FOCUS_OUT:
			focus_changed.emit(false)
		NOTIFICATION_OS_MEMORY_WARNING:
			memory_warning.emit()
		NOTIFICATION_WM_GO_BACK_REQUEST:
			back_requested.emit()
		NOTIFICATION_WM_CLOSE_REQUEST:
			close_requested.emit()

func _enter_background() -> void:
	if _bg:
		return
	_bg = true
	if background_max_fps > 0:
		_saved_max_fps = Engine.max_fps
		Engine.max_fps = background_max_fps
	if _bound_audio and _bound_audio.has_method("stop_bgm"):
		_bound_audio.stop_bgm()
	if _bound_client and _bound_client.has_method("suspend"):
		_bound_client.suspend()
	if pause_tree_on_background:
		get_tree().paused = true
	paused.emit()

func _exit_background() -> void:
	if not _bg:
		return
	_bg = false
	if pause_tree_on_background:
		get_tree().paused = false
	if background_max_fps > 0:
		Engine.max_fps = _saved_max_fps
	if _bound_client and _bound_client.has_method("resume"):
		_bound_client.resume()
	resumed.emit()