import 'dart:async';

import 'package:analytics_sdk/entity/app_lifecycle_event.dart';
import 'package:analytics_sdk/manager/session_manager.dart';
import 'package:analytics_sdk/observer/page_lifecycle_observer.dart';
import 'package:analytics_sdk/utils/environment_info_util.dart';
import 'package:analytics_sdk/utils/logger.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/widgets.dart';

/// 应用生命周期观察者：监听应用前后台切换，用于会话管理与生命周期埋点
class AppLifecycleObserver with WidgetsBindingObserver {
  static final AppLifecycleObserver instance = AppLifecycleObserver._internal();

  factory AppLifecycleObserver() => instance;

  AppLifecycleObserver._internal();

  bool _isInitialized = false;
  void Function(dynamic event)? _track;
  DateTime Function() _now = DateTime.now;
  DateTime? _foregroundStartedAt;
  DateTime? _backgroundStartedAt;
  int _foregroundCountInSid = 0;
  String _foregroundCountSid = '';

  /// 初始化观察者
  void initialize({
    void Function(dynamic event)? track,
    DateTime Function()? now,
  }) {
    if (track != null) _track = track;
    if (now != null) _now = now;
    _foregroundStartedAt ??= _now();
    if (!_isInitialized) {
      WidgetsBinding.instance.addObserver(this);
      _isInitialized = true;
      Logger.analyticsSdk('应用生命周期观察者已初始化');
    }
  }

  /// 销毁观察者
  void dispose() {
    if (_isInitialized) {
      WidgetsBinding.instance.removeObserver(this);
      _isInitialized = false;
      Logger.analyticsSdk('应用生命周期观察者已销毁');
    }
    _track = null;
    _foregroundStartedAt = null;
    _backgroundStartedAt = null;
    _foregroundCountInSid = 0;
    _foregroundCountSid = '';
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    super.didChangeAppLifecycleState(state);

    try {
      switch (state) {
        case AppLifecycleState.resumed:
          if (!kIsWeb) {
            final now = _now();
            final backgroundStartedAt = _backgroundStartedAt;
            final backgroundDurationMs = backgroundStartedAt == null
                ? 0
                : now.difference(backgroundStartedAt).inMilliseconds;
            // 应用从后台恢复前台
            SessionManager.instance.onAppForeground();
            if (backgroundStartedAt != null) {
              _emit(AppLifecycleEvent.warmStart(
                backgroundDurationMs: backgroundDurationMs,
                resumeReason: 'unknown',
              ));
              _emit(AppLifecycleEvent.foreground(
                foregroundCountInSid: _nextForegroundCountInSid(),
              ));
            }
            _backgroundStartedAt = null;
            _foregroundStartedAt = now;
          }
          unawaited(
            EnvironmentInfoUtil.refreshBatteryLevelIfNeeded(force: true),
          );
          unawaited(EnvironmentInfoUtil.refreshRuntimeObservationFields());
          Logger.analyticsSdk('应用恢复前台');
          break;
        case AppLifecycleState.paused:
          if (!kIsWeb) {
            final now = _now();
            final foregroundDurationMs = _foregroundStartedAt == null
                ? 0
                : now.difference(_foregroundStartedAt!).inMilliseconds;
            _emit(AppLifecycleEvent.background(
              foregroundDurationMs: foregroundDurationMs,
              lastActivePageKey: PageLifecycleObserver.currentPageKey,
            ));
            // Android 和 iOS 进入后台均走 paused（iOS 先经过 hidden 再到 paused）
            // 统一在此记录后台开始时间，避免在 hidden 重复记录
            SessionManager.instance.onAppBackground();
            _backgroundStartedAt = now;
          }
          Logger.analyticsSdk('应用进入后台');
          break;
        case AppLifecycleState.inactive:
          // inactive 是过渡状态（进后台和回前台都会经过），不记录后台时间
          Logger.analyticsSdk('应用进入 inactive 状态');
          break;
        case AppLifecycleState.detached:
          if (!kIsWeb) {
            final now = _now();
            _emit(AppLifecycleEvent.terminate(
              lastActivePageKey: PageLifecycleObserver.currentPageKey,
              terminateType: 'unknown',
              sessionDurationMs: _sessionDurationMs(now),
              terminateTs: now.millisecondsSinceEpoch ~/ 1000,
            ));
          }
          Logger.analyticsSdk('应用即将终止');
          break;
        default:
          // Flutter 3.0 没有 hidden；较新版本的 hidden 是过渡状态，
          // 不应影响会话开始或后台时长。
          Logger.analyticsSdk('应用生命周期过渡状态: $state');
          break;
      }
    } catch (e) {
      Logger.analyticsSdk('应用生命周期状态变化处理异常: $e');
      _emit(AppLifecycleEvent.unknown(unknownReason: 'collect_error'));
    }
  }

  void _emit(AppLifecycleEvent event) {
    try {
      final track = _track;
      if (track == null) return;
      track(event);
    } catch (e) {
      Logger.analyticsSdk('app_lifecycle 上报异常，已安全处理: $e');
    }
  }

  int _nextForegroundCountInSid() {
    final sid = SessionManager.instance.currentSessionId ?? '';
    if (sid != _foregroundCountSid) {
      _foregroundCountSid = sid;
      _foregroundCountInSid = 0;
    }
    _foregroundCountInSid += 1;
    return _foregroundCountInSid;
  }

  int _sessionDurationMs(DateTime now) {
    final start = SessionManager.instance.sessionStartTime;
    if (start == null) return 0;
    final duration = now.difference(start).inMilliseconds;
    return duration < 0 ? 0 : duration;
  }
}