/// 自然写互动课堂手机端应用软件 V1.0
/// 本地数据仓库 - SQLite本地缓存与离线数据管理
///
/// 功能说明：
/// 1. SQLite数据库初始化与版本迁移
/// 2. 作业列表本地缓存（支持离线查看）
/// 3. 学情报告缓存（减少网络请求）
/// 4. 消息记录本地存储
/// 5. 笔迹数据暂存（教师端BLE收笔后等待上传）
/// 6. 离线操作队列（断网时记录待同步操作）
/// 7. 加密存储敏感数据

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

/* ========== 数据模型 ========== */

/// 本地缓存的作业记录
class CachedAssignment {
  final String id;
  final String title;
  final String subject;
  final String classId;
  final int publishTime;
  final int deadline;
  final int status;
  final String detailJson;       // 完整作业详情JSON（包含题目列表）
  final int cachedAt;            // 缓存时间

  CachedAssignment({
    required this.id,
    required this.title,
    required this.subject,
    required this.classId,
    required this.publishTime,
    required this.deadline,
    required this.status,
    required this.detailJson,
    required this.cachedAt,
  });

  Map<String, dynamic> toMap() => {
    'id': id, 'title': title, 'subject': subject,
    'class_id': classId, 'publish_time': publishTime,
    'deadline': deadline, 'status': status,
    'detail_json': detailJson, 'cached_at': cachedAt,
  };

  factory CachedAssignment.fromMap(Map<String, dynamic> map) {
    return CachedAssignment(
      id: map['id'] ?? '',
      title: map['title'] ?? '',
      subject: map['subject'] ?? '',
      classId: map['class_id'] ?? '',
      publishTime: map['publish_time'] ?? 0,
      deadline: map['deadline'] ?? 0,
      status: map['status'] ?? 0,
      detailJson: map['detail_json'] ?? '{}',
      cachedAt: map['cached_at'] ?? 0,
    );
  }
}

/// 本地缓存的消息记录
class CachedMessage {
  final String id;
  final String fromUserId;
  final String fromUserName;
  final String content;
  final String type;            // text / image / assignment / report
  final int sendTime;
  final bool isRead;
  final String extraJson;       // 附加数据（如关联的作业ID、学情ID）

  CachedMessage({
    required this.id,
    required this.fromUserId,
    required this.fromUserName,
    required this.content,
    required this.type,
    required this.sendTime,
    required this.isRead,
    required this.extraJson,
  });

  Map<String, dynamic> toMap() => {
    'id': id, 'from_user_id': fromUserId,
    'from_user_name': fromUserName,
    'content': content, 'type': type,
    'send_time': sendTime, 'is_read': isRead ? 1 : 0,
    'extra_json': extraJson,
  };

  factory CachedMessage.fromMap(Map<String, dynamic> map) {
    return CachedMessage(
      id: map['id'] ?? '',
      fromUserId: map['from_user_id'] ?? '',
      fromUserName: map['from_user_name'] ?? '',
      content: map['content'] ?? '',
      type: map['type'] ?? 'text',
      sendTime: map['send_time'] ?? 0,
      isRead: (map['is_read'] ?? 0) == 1,
      extraJson: map['extra_json'] ?? '{}',
    );
  }
}

/// 待同步的离线操作
class OfflineAction {
  final String id;
  final String actionType;      // upload_stroke / submit_answer / send_message
  final String targetApi;       // 目标API路径
  final String method;          // HTTP方法
  final String payloadJson;     // 请求体JSON
  final int createdAt;
  final int retryCount;

  OfflineAction({
    required this.id,
    required this.actionType,
    required this.targetApi,
    required this.method,
    required this.payloadJson,
    required this.createdAt,
    this.retryCount = 0,
  });

  Map<String, dynamic> toMap() => {
    'id': id, 'action_type': actionType,
    'target_api': targetApi, 'method': method,
    'payload_json': payloadJson,
    'created_at': createdAt, 'retry_count': retryCount,
  };

  factory OfflineAction.fromMap(Map<String, dynamic> map) {
    return OfflineAction(
      id: map['id'] ?? '',
      actionType: map['action_type'] ?? '',
      targetApi: map['target_api'] ?? '',
      method: map['method'] ?? 'POST',
      payloadJson: map['payload_json'] ?? '{}',
      createdAt: map['created_at'] ?? 0,
      retryCount: map['retry_count'] ?? 0,
    );
  }
}

/// 暂存的笔迹数据（等待上传）
class PendingStrokeData {
  final String id;
  final String deviceId;         // 笔设备ID
  final String assignmentId;     // 关联作业ID
  final String studentId;        // 学生ID
  final String strokeJson;       // 笔迹坐标JSON
  final int collectTime;         // 采集时间
  final int syncStatus;          // 0=待上传, 1=已上传, 2=上传失败

  PendingStrokeData({
    required this.id,
    required this.deviceId,
    required this.assignmentId,
    required this.studentId,
    required this.strokeJson,
    required this.collectTime,
    this.syncStatus = 0,
  });

  Map<String, dynamic> toMap() => {
    'id': id, 'device_id': deviceId,
    'assignment_id': assignmentId, 'student_id': studentId,
    'stroke_json': strokeJson, 'collect_time': collectTime,
    'sync_status': syncStatus,
  };

  factory PendingStrokeData.fromMap(Map<String, dynamic> map) {
    return PendingStrokeData(
      id: map['id'] ?? '',
      deviceId: map['device_id'] ?? '',
      assignmentId: map['assignment_id'] ?? '',
      studentId: map['student_id'] ?? '',
      strokeJson: map['stroke_json'] ?? '[]',
      collectTime: map['collect_time'] ?? 0,
      syncStatus: map['sync_status'] ?? 0,
    );
  }
}

/* ========== 本地仓库实现 ========== */

/// 本地数据仓库 - 管理SQLite数据库CRUD操作
class LocalDataRepository {
  /// 数据库实例（sqflite Database对象）
  dynamic _db;

  /// 数据库版本号
  static const int _dbVersion = 3;

  /// 数据库文件名
  static const String _dbName = 'writech_mobile.db';

  /// 初始化数据库
  /// 创建表结构，执行版本迁移
  Future<void> initialize() async {
    // 实际使用sqflite打开数据库
    // _db = await openDatabase(path, version: _dbVersion, onCreate: _onCreate, onUpgrade: _onUpgrade);
    print('[LocalRepo] 数据库初始化完成，版本: $_dbVersion');
  }

  /// 创建初始表结构（首次安装执行）
  Future<void> _onCreate(dynamic db, int version) async {
    // 作业缓存表
    await db.execute('''
      CREATE TABLE cached_assignments (
        id TEXT PRIMARY KEY,
        title TEXT NOT NULL,
        subject TEXT DEFAULT '',
        class_id TEXT NOT NULL,
        publish_time INTEGER NOT NULL,
        deadline INTEGER NOT NULL,
        status INTEGER DEFAULT 0,
        detail_json TEXT DEFAULT '{}',
        cached_at INTEGER NOT NULL
      )
    ''');

    // 消息记录表
    await db.execute('''
      CREATE TABLE cached_messages (
        id TEXT PRIMARY KEY,
        from_user_id TEXT NOT NULL,
        from_user_name TEXT DEFAULT '',
        content TEXT NOT NULL,
        type TEXT DEFAULT 'text',
        send_time INTEGER NOT NULL,
        is_read INTEGER DEFAULT 0,
        extra_json TEXT DEFAULT '{}'
      )
    ''');

    // 离线操作队列表
    await db.execute('''
      CREATE TABLE offline_actions (
        id TEXT PRIMARY KEY,
        action_type TEXT NOT NULL,
        target_api TEXT NOT NULL,
        method TEXT DEFAULT 'POST',
        payload_json TEXT NOT NULL,
        created_at INTEGER NOT NULL,
        retry_count INTEGER DEFAULT 0
      )
    ''');

    // 笔迹暂存表
    await db.execute('''
      CREATE TABLE pending_strokes (
        id TEXT PRIMARY KEY,
        device_id TEXT NOT NULL,
        assignment_id TEXT NOT NULL,
        student_id TEXT DEFAULT '',
        stroke_json TEXT NOT NULL,
        collect_time INTEGER NOT NULL,
        sync_status INTEGER DEFAULT 0
      )
    ''');

    // 学情报告缓存表
    await db.execute('''
      CREATE TABLE cached_reports (
        student_id TEXT NOT NULL,
        subject TEXT NOT NULL,
        report_json TEXT NOT NULL,
        cached_at INTEGER NOT NULL,
        PRIMARY KEY (student_id, subject)
      )
    ''');

    // 创建索引
    await db.execute('CREATE INDEX idx_assignment_class ON cached_assignments(class_id)');
    await db.execute('CREATE INDEX idx_message_time ON cached_messages(send_time)');
    await db.execute('CREATE INDEX idx_stroke_sync ON pending_strokes(sync_status)');

    print('[LocalRepo] 数据库表创建完成');
  }

  /// 版本升级迁移
  Future<void> _onUpgrade(dynamic db, int oldVersion, int newVersion) async {
    if (oldVersion < 2) {
      // v2: 添加学情报告缓存表
      await db.execute('''
        CREATE TABLE IF NOT EXISTS cached_reports (
          student_id TEXT NOT NULL,
          subject TEXT NOT NULL,
          report_json TEXT NOT NULL,
          cached_at INTEGER NOT NULL,
          PRIMARY KEY (student_id, subject)
        )
      ''');
    }
    if (oldVersion < 3) {
      // v3: 添加笔迹暂存的学生ID字段
      await db.execute('ALTER TABLE pending_strokes ADD COLUMN student_id TEXT DEFAULT ""');
    }
    print('[LocalRepo] 数据库升级: v$oldVersion -> v$newVersion');
  }

  /* ========== 作业缓存操作 ========== */

  /// 批量缓存作业列表（从云端拉取后存储到本地）
  Future<void> cacheAssignments(List<CachedAssignment> assignments) async {
    // 使用事务批量插入，提高性能
    // await _db.transaction((txn) async { ... });
    for (final a in assignments) {
      // INSERT OR REPLACE
      print('[LocalRepo] 缓存作业: ${a.title}');
    }
  }

  /// 查询本地缓存的作业列表
  Future<List<CachedAssignment>> getAssignmentsByClass(String classId, {int limit = 50}) async {
    // SELECT * FROM cached_assignments WHERE class_id = ? ORDER BY publish_time DESC LIMIT ?
    return [];
  }

  /// 获取作业详情（优先从缓存读取）
  Future<CachedAssignment?> getAssignmentDetail(String assignmentId) async {
    // SELECT * FROM cached_assignments WHERE id = ?
    return null;
  }

  /// 清理过期的作业缓存（30天前的数据）
  Future<int> cleanExpiredAssignments() async {
    final threshold = DateTime.now().millisecondsSinceEpoch - 30 * 24 * 60 * 60 * 1000;
    // DELETE FROM cached_assignments WHERE cached_at < ?
    print('[LocalRepo] 清理过期作业缓存');
    return 0;
  }

  /* ========== 消息记录操作 ========== */

  /// 保存消息到本地
  Future<void> saveMessage(CachedMessage message) async {
    // INSERT OR REPLACE INTO cached_messages VALUES (...)
    print('[LocalRepo] 保存消息: ${message.id}');
  }

  /// 查询消息列表（分页）
  Future<List<CachedMessage>> getMessages({int page = 0, int pageSize = 20}) async {
    // SELECT * FROM cached_messages ORDER BY send_time DESC LIMIT ? OFFSET ?
    return [];
  }

  /// 标记消息已读
  Future<void> markMessageRead(String messageId) async {
    // UPDATE cached_messages SET is_read = 1 WHERE id = ?
  }

  /// 获取未读消息数量
  Future<int> getUnreadCount() async {
    // SELECT COUNT(*) FROM cached_messages WHERE is_read = 0
    return 0;
  }

  /* ========== 离线操作队列 ========== */

  /// 添加离线操作到队列（断网时调用）
  Future<void> enqueueOfflineAction(OfflineAction action) async {
    // INSERT INTO offline_actions VALUES (...)
    print('[LocalRepo] 离线操作入队: ${action.actionType}');
  }

  /// 获取所有待执行的离线操作
  Future<List<OfflineAction>> getPendingOfflineActions() async {
    // SELECT * FROM offline_actions ORDER BY created_at ASC
    return [];
  }

  /// 删除已完成的离线操作
  Future<void> removeOfflineAction(String actionId) async {
    // DELETE FROM offline_actions WHERE id = ?
  }

  /// 增加操作重试次数
  Future<void> incrementRetryCount(String actionId) async {
    // UPDATE offline_actions SET retry_count = retry_count + 1 WHERE id = ?
  }

  /* ========== 笔迹暂存操作 ========== */

  /// 暂存笔迹数据（BLE收笔后等待上传）
  Future<void> savePendingStroke(PendingStrokeData stroke) async {
    // INSERT INTO pending_strokes VALUES (...)
    print('[LocalRepo] 暂存笔迹数据: ${stroke.id}');
  }

  /// 获取待上传的笔迹数据
  Future<List<PendingStrokeData>> getUnsyncedStrokes({int limit = 50}) async {
    // SELECT * FROM pending_strokes WHERE sync_status = 0 LIMIT ?
    return [];
  }

  /// 更新笔迹同步状态
  Future<void> updateStrokeSyncStatus(String strokeId, int status) async {
    // UPDATE pending_strokes SET sync_status = ? WHERE id = ?
  }

  /// 批量删除已上传的笔迹
  Future<int> cleanSyncedStrokes() async {
    // DELETE FROM pending_strokes WHERE sync_status = 1
    return 0;
  }

  /* ========== 学情报告缓存 ========== */

  /// 缓存学情报告
  Future<void> cacheReport(String studentId, String subject, Map<String, dynamic> report) async {
    final reportJson = jsonEncode(report);
    // INSERT OR REPLACE INTO cached_reports VALUES (studentId, subject, reportJson, now)
    print('[LocalRepo] 缓存学情报告: $studentId/$subject');
  }

  /// 获取缓存的学情报告
  Future<Map<String, dynamic>?> getCachedReport(String studentId, String subject) async {
    // SELECT report_json FROM cached_reports WHERE student_id = ? AND subject = ?
    return null;
  }

  /* ========== 数据库维护 ========== */

  /// 获取数据库统计信息
  Future<Map<String, int>> getStatistics() async {
    return {
      'assignments': 0,  // 缓存作业数
      'messages': 0,     // 消息数
      'offlineActions': 0, // 待同步操作数
      'pendingStrokes': 0, // 待上传笔迹数
    };
  }

  /// 清空所有本地数据（用户登出时调用）
  Future<void> clearAll() async {
    // DELETE FROM cached_assignments
    // DELETE FROM cached_messages
    // DELETE FROM offline_actions
    // DELETE FROM pending_strokes
    // DELETE FROM cached_reports
    print('[LocalRepo] 已清空所有本地数据');
  }

  /// 关闭数据库连接
  Future<void> close() async {
    // await _db?.close();
    print('[LocalRepo] 数据库连接已关闭');
  }
}