class Message {
  final String role; // 'user' or 'assistant'
  final String content;
  final DateTime timestamp;
  final bool isLoading;

  Message({
    required this.role,
    required this.content,
    required this.timestamp,
    this.isLoading = false,
  });

  // 从JSON构造函数
  factory Message.fromJson(Map<String, dynamic> json) {
    return Message(
      role: json['role'] as String,
      content: json['content'] as String,
      timestamp: DateTime.parse(json['timestamp'] as String),
      isLoading: json['isLoading'] as bool? ?? false,
    );
  }

  // 转换为JSON
  Map<String, dynamic> toJson() {
    return {
      'role': role,
      'content': content,
      'timestamp': timestamp.toIso8601String(),
      'isLoading': isLoading,
    };
  }

  // 创建一个加载中的消息
  factory Message.loading() {
    return Message(
      role: 'assistant',
      content: '',
      timestamp: DateTime.now(),
      isLoading: true,
    );
  }

  // 复制并修改
  Message copyWith({
    String? role,
    String? content,
    DateTime? timestamp,
    bool? isLoading,
  }) {
    return Message(
      role: role ?? this.role,
      content: content ?? this.content,
      timestamp: timestamp ?? this.timestamp,
      isLoading: isLoading ?? this.isLoading,
    );
  }
}