// 同步引擎 — Web 平台实现（无 Isar 持久化）
//
// Web 平台上 Isar 不可用，操作队列仅保存在内存中。
// 核心同步逻辑与原生版一致，仅持久化部分为空实现。

import 'dart:async';
import 'dart:convert';
import 'dart:collection';

import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:flutter/foundation.dart';

import '../remote/api_client.dart';

/// 同步操作类型
enum SyncOperationType {
  create('POST'),
  update('PUT'),
  delete('DELETE');

  const SyncOperationType(this.httpMethod);
  final String httpMethod;
}

/// 同步状态
enum SyncStatus {
  idle,
  syncing,
  paused,
  error,
}

/// 待同步操作
class PendingOperation {
  final String id;
  final SyncOperationType type;
  final String endpoint;
  final Map<String, dynamic> data;
  final int version;
  final DateTime createdAt;
  final int retryCount;

  static const int maxRetryCount = 5;

  const PendingOperation({
    required this.id,
    required this.type,
    required this.endpoint,
    required this.data,
    required this.version,
    required this.createdAt,
    this.retryCount = 0,
  });

  PendingOperation copyWith({
    String? id,
    SyncOperationType? type,
    String? endpoint,
    Map<String, dynamic>? data,
    int? version,
    DateTime? createdAt,
    int? retryCount,
  }) =>
      PendingOperation(
        id: id ?? this.id,
        type: type ?? this.type,
        endpoint: endpoint ?? this.endpoint,
        data: data ?? this.data,
        version: version ?? this.version,
        createdAt: createdAt ?? this.createdAt,
        retryCount: retryCount ?? this.retryCount,
      );

  bool get isExhausted => retryCount >= maxRetryCount;
}

/// 同步引擎 — Web 版（内存队列，无持久化）
class SyncEngine {
  final ApiClient _apiClient;
  final Queue<PendingOperation> _pendingQueue = Queue();
  StreamSubscription<List<ConnectivityResult>>? _connectivitySub;

  SyncStatus _status = SyncStatus.idle;
  String? _lastError;

  SyncEngine({required ApiClient apiClient}) : _apiClient = apiClient;

  SyncStatus get status => _status;
  String? get lastError => _lastError;
  int get pendingCount => _pendingQueue.length;
  bool get isSyncing => _status == SyncStatus.syncing;

  /// 入队待同步操作 — 私密日记（is_private=true）不入队
  void enqueue(PendingOperation operation) {
    // 防御性检查：私密日记仅保存在本地，不上传后端
    final isPrivate = operation.data['is_private'] as bool? ?? false;
    if (isPrivate) {
      debugPrint('SyncEngine.enqueue: 跳过私密日记 ${operation.id}');
      return;
    }

    _pendingQueue.add(operation);
    if (_status == SyncStatus.idle) {
      _status = SyncStatus.paused;
    }
  }

  void enqueueAll(List<PendingOperation> operations) {
    for (final op in operations) {
      _pendingQueue.add(op);
    }
    if (_status == SyncStatus.idle && _pendingQueue.isNotEmpty) {
      _status = SyncStatus.paused;
    }
  }

  Future<void> trySync() async {
    if (_status == SyncStatus.syncing) return;
    if (_pendingQueue.isEmpty) {
      _status = SyncStatus.idle;
      return;
    }

    final connectivity = Connectivity();
    final result = await connectivity.checkConnectivity();
    final isOnline = result.any((r) => r != ConnectivityResult.none);
    if (!isOnline) {
      _status = SyncStatus.paused;
      _lastError = '网络不可用';
      return;
    }

    _status = SyncStatus.syncing;
    _lastError = null;

    while (_pendingQueue.isNotEmpty) {
      final operation = _pendingQueue.removeFirst();

      try {
        await _executeOperation(operation);
      } on OfflineException {
        _pendingQueue.addFirst(operation);
        _status = SyncStatus.paused;
        _lastError = '同步中断：网络不可用';
        return;
      } catch (e) {
        debugPrint('SyncEngine.trySync 操作失败: $e');
        final retried = operation.copyWith(retryCount: operation.retryCount + 1);

        if (retried.isExhausted) {
          _lastError = '操作同步失败（已耗尽重试次数）: ${operation.endpoint}';
          continue;
        }

        _pendingQueue.addFirst(retried);
        _status = SyncStatus.error;
        _lastError = '同步失败: $e';
        return;
      }
    }

    _status = SyncStatus.idle;
    _lastError = null;
  }

  Future<void> _executeOperation(PendingOperation operation) async {
    switch (operation.type) {
      case SyncOperationType.create:
        await _apiClient.post(operation.endpoint, data: operation.data);
      case SyncOperationType.update:
        await _apiClient.put(operation.endpoint, data: operation.data);
      case SyncOperationType.delete:
        await _apiClient.delete(operation.endpoint);
    }
  }

  void clear() {
    _pendingQueue.clear();
    _status = SyncStatus.idle;
    _lastError = null;
  }

  List<PendingOperation> get snapshot => _pendingQueue.toList();

  /// Web 平台：持久化为空操作（队列仅保存在内存中）
  Future<void> persistPendingQueue() async {}

  /// Web 平台：恢复队列为空操作（无持久化数据）
  Future<void> restorePendingQueue() async {}

  void startAutoSync() {
    _connectivitySub = Connectivity().onConnectivityChanged.listen((result) {
      final isOnline = result.any((r) => r != ConnectivityResult.none);
      if (isOnline && _pendingQueue.isNotEmpty && _status != SyncStatus.syncing) {
        debugPrint('SyncEngine: 网络恢复，开始同步 ${_pendingQueue.length} 个操作');
        trySync();
      }
    });
  }

  void dispose() {
    _connectivitySub?.cancel();
    _connectivitySub = null;
  }

  String _encodeJson(Map<String, dynamic> data) {
    try {
      return jsonEncode(data);
    } catch (_) {
      return '{}';
    }
  }

  Map<String, dynamic> _decodeJson(String json) {
    try {
      return jsonDecode(json) as Map<String, dynamic>;
    } catch (_) {
      return {};
    }
  }
}