const sqlite3 = require('sqlite3').verbose();
const path = require('path');
const fs = require('fs');

class Database {
  constructor() {
    this.db = null;
    this.dbPath = process.env.DB_PATH || path.join(__dirname, '../database/chat.db');
  }

  /**
   * 初始化数据库连接
   */
  async initialize() {
    try {
      // 确保数据库目录存在
      const dbDir = path.dirname(this.dbPath);
      if (!fs.existsSync(dbDir)) {
        fs.mkdirSync(dbDir, { recursive: true });
      }

      // 创建数据库连接
      this.db = new sqlite3.Database(this.dbPath, (err) => {
        if (err) {
          console.error('数据库连接失败:', err.message);
          throw err;
        }
        console.log('SQLite数据库连接成功');
      });

      // 启用外键约束
      await this.run('PRAGMA foreign_keys = ON');
      
      // 初始化数据库表结构
      await this.initializeTables();
      
      return this.db;
    } catch (error) {
      console.error('数据库初始化失败:', error);
      throw error;
    }
  }

  /**
   * 初始化数据库表结构
   */
  async initializeTables() {
    try {
      const schemaPath = path.join(__dirname, '../database/schema.sql');
      const schema = fs.readFileSync(schemaPath, 'utf8');
      
      // 分割SQL语句并执行
      const statements = schema.split(';').filter(stmt => stmt.trim());
      
      for (const statement of statements) {
        if (statement.trim()) {
          await this.run(statement);
        }
      }
      
      console.log('数据库表结构初始化完成');
    } catch (error) {
      console.error('数据库表结构初始化失败:', error);
      throw error;
    }
  }

  /**
   * 执行SQL语句 (INSERT, UPDATE, DELETE)
   */
  run(sql, params = []) {
    return new Promise((resolve, reject) => {
      this.db.run(sql, params, function(err) {
        if (err) {
          reject(err);
        } else {
          resolve({ id: this.lastID, changes: this.changes });
        }
      });
    });
  }

  /**
   * 查询单条记录
   */
  get(sql, params = []) {
    return new Promise((resolve, reject) => {
      this.db.get(sql, params, (err, row) => {
        if (err) {
          reject(err);
        } else {
          resolve(row);
        }
      });
    });
  }

  /**
   * 查询多条记录
   */
  all(sql, params = []) {
    return new Promise((resolve, reject) => {
      this.db.all(sql, params, (err, rows) => {
        if (err) {
          reject(err);
        } else {
          resolve(rows);
        }
      });
    });
  }

  /**
   * 开始事务
   */
  async beginTransaction() {
    await this.run('BEGIN TRANSACTION');
  }

  /**
   * 提交事务
   */
  async commit() {
    await this.run('COMMIT');
  }

  /**
   * 回滚事务
   */
  async rollback() {
    await this.run('ROLLBACK');
  }

  /**
   * 关闭数据库连接
   */
  close() {
    return new Promise((resolve, reject) => {
      if (this.db) {
        this.db.close((err) => {
          if (err) {
            reject(err);
          } else {
            console.log('数据库连接已关闭');
            resolve();
          }
        });
      } else {
        resolve();
      }
    });
  }
}

// 创建单例实例
const database = new Database();

module.exports = database;