llm-chat/backend/models/Message.js

const database = require('./database');

class Message {
  constructor(data = {}) {
    this.id = data.id;
    this.conversation_id = data.conversation_id;
    this.role = data.role; // 'user' 或 'assistant'
    this.content = data.content;
    this.timestamp = data.timestamp;
  }

  /**
   * 创建新消息
   */
  static async create(conversationId, role, content) {
    try {
      // 验证角色
      if (!['user', 'assistant'].includes(role)) {
        throw new Error('无效的消息角色');
      }

      const sql = `
        INSERT INTO messages (conversation_id, role, content, timestamp) 
        VALUES (?, ?, ?, datetime('now'))
      `;
      const result = await database.run(sql, [conversationId, role, content]);
      
      // 返回新创建的消息
      return await Message.findById(result.id);
    } catch (error) {
      console.error('创建消息失败:', error);
      throw error;
    }
  }

  /**
   * 根据ID查找消息
   */
  static async findById(id) {
    try {
      const sql = 'SELECT * FROM messages WHERE id = ?';
      const row = await database.get(sql, [id]);
      return row ? new Message(row) : null;
    } catch (error) {
      console.error('查找消息失败:', error);
      throw error;
    }
  }

  /**
   * 获取对话的所有消息（按时间正序）
   */
  static async findByConversationId(conversationId, limit = 100, offset = 0) {
    try {
      const sql = `
        SELECT * FROM messages 
        WHERE conversation_id = ? 
        ORDER BY timestamp ASC 
        LIMIT ? OFFSET ?
      `;
      const rows = await database.all(sql, [conversationId, limit, offset]);
      return rows.map(row => new Message(row));
    } catch (error) {
      console.error('获取对话消息失败:', error);
      throw error;
    }
  }

  /**
   * 获取对话的最近N条消息（用于构建上下文）
   */
  static async getRecentMessages(conversationId, limit = 10) {
    try {
      const sql = `
        SELECT * FROM messages 
        WHERE conversation_id = ? 
        ORDER BY timestamp DESC 
        LIMIT ?
      `;
      const rows = await database.all(sql, [conversationId, limit]);
      // 返回正序排列的消息
      return rows.reverse().map(row => new Message(row));
    } catch (error) {
      console.error('获取最近消息失败:', error);
      throw error;
    }
  }

  /**
   * 获取对话的消息总数
   */
  static async getMessageCount(conversationId) {
    try {
      const sql = 'SELECT COUNT(*) as count FROM messages WHERE conversation_id = ?';
      const result = await database.get(sql, [conversationId]);
      return result.count;
    } catch (error) {
      console.error('获取消息数量失败:', error);
      throw error;
    }
  }

  /**
   * 删除指定消息
   */
  static async delete(id) {
    try {
      const sql = 'DELETE FROM messages WHERE id = ?';
      const result = await database.run(sql, [id]);
      
      if (result.changes === 0) {
        throw new Error('消息不存在');
      }
      
      return true;
    } catch (error) {
      console.error('删除消息失败:', error);
      throw error;
    }
  }

  /**
   * 删除对话的所有消息
   */
  static async deleteByConversationId(conversationId) {
    try {
      const sql = 'DELETE FROM messages WHERE conversation_id = ?';
      const result = await database.run(sql, [conversationId]);
      return result.changes;
    } catch (error) {
      console.error('删除对话消息失败:', error);
      throw error;
    }
  }

  /**
   * 批量创建消息
   */
  static async createBatch(messages) {
    try {
      await database.beginTransaction();
      
      const results = [];
      for (const messageData of messages) {
        const { conversationId, role, content } = messageData;
        const message = await Message.create(conversationId, role, content);
        results.push(message);
      }
      
      await database.commit();
      return results;
    } catch (error) {
      await database.rollback();
      console.error('批量创建消息失败:', error);
      throw error;
    }
  }

  /**
   * 搜索消息内容
   */
  static async search(query, conversationId = null, limit = 50) {
    try {
      let sql = `
        SELECT m.*, c.title as conversation_title 
        FROM messages m 
        JOIN conversations c ON m.conversation_id = c.id 
        WHERE m.content LIKE ?
      `;
      const params = [`%${query}%`];
      
      if (conversationId) {
        sql += ' AND m.conversation_id = ?';
        params.push(conversationId);
      }
      
      sql += ' ORDER BY m.timestamp DESC LIMIT ?';
      params.push(limit);
      
      const rows = await database.all(sql, params);
      return rows.map(row => ({
        ...new Message(row),
        conversation_title: row.conversation_title
      }));
    } catch (error) {
      console.error('搜索消息失败:', error);
      throw error;
    }
  }

  /**
   * 获取用户消息和AI回复的对话历史（用于LLM上下文）
   */
  static async getConversationHistory(conversationId, maxTokens = 4000) {
    try {
      // 简单估算：每个字符约占1个token，中文可能占更多
      const messages = await Message.getRecentMessages(conversationId, 20);
      
      const history = [];
      let totalLength = 0;
      
      // 从最新消息开始，控制总长度
      for (let i = messages.length - 1; i >= 0; i--) {
        const message = messages[i];
        const messageLength = message.content.length;
        
        if (totalLength + messageLength > maxTokens && history.length > 0) {
          break;
        }
        
        history.unshift({
          role: message.role,
          content: message.content
        });
        
        totalLength += messageLength;
      }
      
      return history;
    } catch (error) {
      console.error('获取对话历史失败:', error);
      throw error;
    }
  }
}

module.exports = Message;