import 'json_util.dart';

/// 会话列表项（不含消息）
class ChatSessionItem {
  final int id;
  final String title;
  final String updateTime;

  /// 本会话绑定的人设 id。null = 内置默认人设。
  ///
  /// 会话的人设在**新建时确定、之后不可改** —— 一次对话从头到尾是同一个人。
  final int? personaId;

  /// 人设显示名。人设被删了会回落成「默认人设」，历史会话不会因此打不开
  final String personaName;

  /// 人设头像相对路径。null = 用默认头像
  final String? personaAvatar;

  const ChatSessionItem({
    required this.id,
    required this.title,
    required this.updateTime,
    this.personaId,
    this.personaName = '默认人设',
    this.personaAvatar,
  });

  factory ChatSessionItem.fromJson(Map<String, dynamic> json) {
    return ChatSessionItem(
      id: asInt(json['id']),
      title: asNonEmpty(json['title'], '新对话'),
      updateTime: formatDateTime(json['updateTime']),
      personaId: asNullableInt(json['personaId']),
      personaName: asNonEmpty(json['personaName'], '默认人设'),
      personaAvatar: asNonEmpty(json['personaAvatar'], ''),
    );
  }
}

/// 会话里的一条消息。工具调用的中间过程后端不入库，所以只有 user / assistant
class ChatMessageItem {
  final int id;
  final String role;
  final String content;

  const ChatMessageItem({
    required this.id,
    required this.role,
    required this.content,
  });

  bool get isUser => role == 'user';

  factory ChatMessageItem.fromJson(Map<String, dynamic> json) {
    return ChatMessageItem(
      id: asInt(json['id']),
      role: asString(json['role'], fallback: 'assistant'),
      content: asString(json['content']),
    );
  }
}

/// 页面上的一个气泡。
///
/// 和 [ChatMessageItem] 的区别：这个没有 id、带 streaming 标记，
/// 因为正在生成的那条回答还没落库。
class ChatBubble {
  final String role;
  final String content;

  /// 正在生成中（末尾会显示光标 / 工具提示）
  final bool streaming;

  const ChatBubble({
    required this.role,
    required this.content,
    this.streaming = false,
  });

  const ChatBubble.user(String content) : this(role: 'user', content: content);

  const ChatBubble.assistant(String content, {bool streaming = false})
      : this(role: 'assistant', content: content, streaming: streaming);

  bool get isUser => role == 'user';

  ChatBubble copyWith({String? content, bool? streaming}) {
    return ChatBubble(
      role: role,
      content: content ?? this.content,
      streaming: streaming ?? this.streaming,
    );
  }

  factory ChatBubble.fromItem(ChatMessageItem item) =>
      ChatBubble(role: item.role, content: item.content);
}

/// SSE 事件类型
enum AiEventType { delta, tool, done, error }

/// 一次 SSE 事件。后端只会发这四种，见 AiChatService。
class AiEvent {
  final AiEventType type;

  /// delta：本次新增的文本
  final String? content;

  /// tool：正在调用的工具名
  final String? toolName;

  /// done：会话 ID（新会话时后端才刚创建，App 要靠它接着聊）
  final int? sessionId;

  /// error：错误提示
  final String? message;

  const AiEvent._(this.type, {this.content, this.toolName, this.sessionId, this.message});

  const AiEvent.delta(String content) : this._(AiEventType.delta, content: content);

  const AiEvent.tool(String name) : this._(AiEventType.tool, toolName: name);

  const AiEvent.done(int? sessionId) : this._(AiEventType.done, sessionId: sessionId);

  const AiEvent.error(String message) : this._(AiEventType.error, message: message);
}