import 'dart:convert';

import 'package:crypto/crypto.dart';

/// Session 内自动汇总指标。
///
/// 只记录成功进入 SDK 队列的事件。这里不采集滚动轨迹、键盘输入内容、
/// 长按、双指缩放等高风险/不稳定指标，避免为了汇总事件扩大监听面。
class SessionMetricsManager {
  static final SessionMetricsManager instance =
      SessionMetricsManager._internal();

  factory SessionMetricsManager() => instance;

  SessionMetricsManager._internal();

  static const int _maxBehaviorSequence = 200;
  static const int _maxPageStayRecords = 100;

  static const Set<String> _nonBusinessEvents = {
    'sdk_init',
    'app_lifecycle',
    'network_state_change',
    'app_session_summary',
    'app_page_view',
    'page_click',
    'navigation',
    'page_lifecycle',
  };

  String _sid = '';
  int _eventCountTotal = 0;
  int _businessEventCount = 0;
  int _foregroundCount = 0;
  int _backgroundCountInSid = 0;
  int _pageViewCount = 0;
  int _pageClickCount = 0;
  int _networkChangeCount = 0;
  String _lastEventName = '';
  final Set<String> _pageKeys = <String>{};
  final Set<String> _pagesWithInteraction = <String>{};
  final List<String> _behaviorSequence = <String>[];
  final List<_PageStayRecord> _activePageStays = <_PageStayRecord>[];
  final List<_PageStayRecord> _completedPageStays = <_PageStayRecord>[];

  void recordAcceptedEvent(Map<String, dynamic> event) {
    final eventName = event['event']?.toString() ?? '';
    if (eventName.isEmpty || eventName == 'app_session_summary') return;

    final sid = event['sid']?.toString() ?? '';
    if (sid != _sid) {
      reset(sid: sid);
    }

    _eventCountTotal += 1;
    _lastEventName = eventName;
    _recordBehaviorSequence(eventName, _payloadPageKey(event));

    if (!_nonBusinessEvents.contains(eventName)) {
      _businessEventCount += 1;
    }

    if (eventName == 'app_page_view') {
      _pageViewCount += 1;
      _recordPageKey(event);
    } else if (eventName == 'page_click') {
      _pageClickCount += 1;
      _recordPageKey(event);
      final pageKey = _payloadPageKey(event);
      if (pageKey.isNotEmpty) _pagesWithInteraction.add(pageKey);
    } else if (eventName == 'app_lifecycle') {
      final key = _payloadString(event, 'lifecycle_event_key',
          fallback: event['lifecycle_event_key']);
      if (key == 'foreground') {
        _foregroundCount += 1;
      } else if (key == 'background') {
        _backgroundCountInSid += 1;
      }
    } else if (eventName == 'network_state_change') {
      _networkChangeCount += 1;
    }
  }

  void recordPageEnter({
    required String pageKey,
    required String pageName,
    required DateTime enterTime,
  }) {
    final normalizedPageKey = pageKey.trim();
    if (normalizedPageKey.isEmpty) return;
    _pageKeys.add(normalizedPageKey);
    _closeActivePageStays(exitTime: enterTime);
    _activePageStays.add(_PageStayRecord(
      pageKey: normalizedPageKey,
      pageName: pageName,
      enterTime: enterTime,
    ));
  }

  void recordPageExit({
    required String pageKey,
    required String pageName,
    required DateTime enterTime,
    required DateTime exitTime,
  }) {
    final normalizedPageKey = pageKey.trim();
    if (normalizedPageKey.isEmpty) return;
    _pageKeys.add(normalizedPageKey);

    final index = _findActivePageStayIndex(normalizedPageKey, enterTime);
    if (index < 0) return;
    final record = _activePageStays.removeAt(index);
    _completedPageStays.add(record.close(
      exitTime: exitTime,
      hasInteraction: _pagesWithInteraction.contains(normalizedPageKey),
    ));
    _trimCompletedPageStays();
  }

  SessionMetricsSnapshot snapshot({DateTime? endedAt}) {
    final now = endedAt ?? DateTime.now();
    return SessionMetricsSnapshot(
      eventCountTotal: _eventCountTotal,
      businessEventCount: _businessEventCount,
      foregroundCount: _foregroundCount,
      backgroundCountInSid: _backgroundCountInSid,
      pageCount: _pageKeys.length,
      pageViewCount: _pageViewCount,
      pageClickCount: _pageClickCount,
      networkChangeCount: _networkChangeCount,
      sessionSid: _sid,
      lastEventName: _lastEventName,
      pageStayList: _pageStayList(now),
      behaviorSequenceHash: _behaviorSequenceHash(),
    );
  }

  void reset({String sid = ''}) {
    _sid = sid;
    _eventCountTotal = 0;
    _businessEventCount = 0;
    _foregroundCount = 0;
    _backgroundCountInSid = 0;
    _pageViewCount = 0;
    _pageClickCount = 0;
    _networkChangeCount = 0;
    _lastEventName = '';
    _pageKeys.clear();
    _pagesWithInteraction.clear();
    _behaviorSequence.clear();
    _activePageStays.clear();
    _completedPageStays.clear();
  }

  void _recordPageKey(Map<String, dynamic> event) {
    final pageKey = _payloadPageKey(event);
    if (pageKey.isNotEmpty) _pageKeys.add(pageKey);
  }

  String _payloadPageKey(Map<String, dynamic> event) {
    return _payloadString(event, 'page_key');
  }

  String _payloadString(
    Map<String, dynamic> event,
    String key, {
    Object? fallback,
  }) {
    final payload = event['payload'];
    if (payload is Map) {
      final value = payload[key]?.toString().trim() ?? '';
      if (value.isNotEmpty) return value;
    }
    return fallback?.toString().trim() ?? '';
  }

  void _recordBehaviorSequence(String eventName, String pageKey) {
    final token = pageKey.isEmpty ? eventName : '$eventName:$pageKey';
    _behaviorSequence.add(token);
    if (_behaviorSequence.length > _maxBehaviorSequence) {
      _behaviorSequence.removeAt(0);
    }
  }

  String _behaviorSequenceHash() {
    if (_behaviorSequence.isEmpty) return '';
    return sha256.convert(utf8.encode(_behaviorSequence.join('|'))).toString();
  }

  List<Map<String, dynamic>> _pageStayList(DateTime endedAt) {
    final all = [
      ..._completedPageStays,
      ..._activePageStays.map((record) => record.close(
            exitTime: endedAt,
            hasInteraction: _pagesWithInteraction.contains(record.pageKey),
          )),
    ]..sort((a, b) => a.enterTime.compareTo(b.enterTime));
    final capped = all.length > _maxPageStayRecords
        ? all.sublist(all.length - _maxPageStayRecords)
        : all;
    return capped.map((record) => record.toJson()).toList();
  }

  void _closeActivePageStays({required DateTime exitTime}) {
    if (_activePageStays.isEmpty) return;
    for (final record in _activePageStays) {
      _completedPageStays.add(record.close(
        exitTime: exitTime,
        hasInteraction: _pagesWithInteraction.contains(record.pageKey),
      ));
    }
    _activePageStays.clear();
    _trimCompletedPageStays();
  }

  int _findActivePageStayIndex(String pageKey, DateTime enterTime) {
    for (var i = _activePageStays.length - 1; i >= 0; i--) {
      final record = _activePageStays[i];
      if (record.pageKey == pageKey && record.enterTime == enterTime) return i;
    }
    return -1;
  }

  void _trimCompletedPageStays() {
    while (_completedPageStays.length > _maxPageStayRecords) {
      _completedPageStays.removeAt(0);
    }
  }
}

class SessionMetricsSnapshot {
  final int eventCountTotal;
  final int businessEventCount;
  final int foregroundCount;
  final int backgroundCountInSid;
  final int pageCount;
  final int pageViewCount;
  final int pageClickCount;
  final int networkChangeCount;
  final String sessionSid;
  final String lastEventName;
  final List<Map<String, dynamic>> pageStayList;
  final String behaviorSequenceHash;

  const SessionMetricsSnapshot({
    required this.eventCountTotal,
    required this.businessEventCount,
    required this.foregroundCount,
    required this.backgroundCountInSid,
    required this.pageCount,
    required this.pageViewCount,
    required this.pageClickCount,
    required this.networkChangeCount,
    required this.sessionSid,
    required this.lastEventName,
    required this.pageStayList,
    required this.behaviorSequenceHash,
  });
}

class _PageStayRecord {
  final String pageKey;
  final String pageName;
  final DateTime enterTime;
  final DateTime? exitTime;
  final bool hasInteraction;

  const _PageStayRecord({
    required this.pageKey,
    required this.pageName,
    required this.enterTime,
    this.exitTime,
    this.hasInteraction = false,
  });

  _PageStayRecord close({
    required DateTime exitTime,
    required bool hasInteraction,
  }) {
    return _PageStayRecord(
      pageKey: pageKey,
      pageName: pageName,
      enterTime: enterTime,
      exitTime: exitTime,
      hasInteraction: hasInteraction,
    );
  }

  Map<String, dynamic> toJson() {
    final endTime = exitTime ?? DateTime.now();
    final stayDurationMs = endTime.difference(enterTime).inMilliseconds;
    return {
      'page_key': pageKey,
      'page_name': pageName,
      'stay_duration_ms': stayDurationMs < 0 ? 0 : stayDurationMs,
      'enter_time': enterTime.millisecondsSinceEpoch ~/ 1000,
      'has_interaction': hasInteraction ? 1 : 0,
    };
  }
}