add sqllite utils

lib/config/database_helper.dart

@@ -0,0 +1,56 @@
+import 'dart:io';
+import 'package:sqflite/sqflite.dart';
+import 'package:path/path.dart';
+import 'package:path_provider/path_provider.dart';
+
+class DatabaseHelper {
+  static final DatabaseHelper _instance = DatabaseHelper._internal();
+  factory DatabaseHelper() => _instance;
+  static Database? _database;
+
+  DatabaseHelper._internal();
+
+  Future<Database> get database async {
+    if (_database != null) return _database!;
+    _database = await _initDatabase();
+    return _database!;
+  }
+
+  Future<Database> _initDatabase() async {
+    Directory documentsDirectory = await getApplicationDocumentsDirectory();
+    String path = join(documentsDirectory.path, 'chat.db');
+    return await openDatabase(
+      path,
+      version: 1,
+      onCreate: _onCreate,
+    );
+  }
+
+  Future<void> _onCreate(Database db, int version) async {
+    await db.execute('''
+      CREATE TABLE messages (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        role TEXT NOT NULL,
+        message TEXT NOT NULL,
+        timestamp INTEGER DEFAULT (strftime('%s', 'now'))
+      ''');
+  }
+
+  // 插入一条消息
+  Future<int> insertMessage(Map<String, dynamic> message) async {
+    Database db = await database;
+    return await db.insert('messages', message);
+  }
+
+  // 获取所有消息（按时间排序）
+  Future<List<Map<String, dynamic>>> getMessages() async {
+    Database db = await database;
+    return await db.query('messages', orderBy: 'timestamp ASC');
+  }
+
+  // 删除所有消息
+  Future<int> clearMessages() async {
+    Database db = await database;
+    return await db.delete('messages');
+  }
+}