OpenAIのAssistant APIを使ってFlutter アプリを作ってみた

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;


void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Chatbot App',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        fontFamily: 'NotoSansJP',
      ),
      home: ChatScreen(),
    );
  }
}

class ChatScreen extends StatefulWidget {
  @override
  State createState() => ChatScreenState();
}

class ChatScreenState extends State<ChatScreen> {
  final TextEditingController _controller = TextEditingController();
  final List<Map<String, dynamic>> _messages = [];

  String api_key= '<Your API key>';
  String assistant_id = '<Your Assitant ID>';
  String thread_id ='';
  String message_id='';
  String run_id='';

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_) async{
      await _createThread().then((result) {
            setState(() {
                _messages.add({'text': 'こんにちは、お話ししましょう。', 'user': false});
            });
        
      });
    });
  }

  
  void _sendMessage() async {
    String userMessage = _controller.text;

    setState(() {
      _messages.add({'text': userMessage, 'user': true});
    });

    _controller.clear();

    message_id = await _createMessage(userMessage);
    run_id = await _createRun();
    await Future.delayed(Duration(seconds: 3)); // Assistantメッセージがセットされないことがあったので少しディレイを入れています。
    String botReply = await getAssistantReply(userMessage);
    
    setState(() {
      _messages.add({'text': botReply, 'user': false});
    });
  }


  Future<String> getAssistantReply(String message) async{

    final response = await http.get(
      Uri.parse('https://api.openai.com/v1/threads/$thread_id/messages?order=desc'), 
      headers: {
        'Content-Type': 'application/json',
        'OpenAI-Beta': 'assistants=v1',
        'Authorization': 'Bearer $api_key' , 
      },
    );

    if (response.statusCode == 200) {
      Map<String, dynamic> data = json.decode(utf8.decode(response.bodyBytes));
      return data['data'][0]['content'][0]['text']['value'];
    } else {
      throw Exception('Failed to load response');
    }

  }


  Future<String>  _createThread() async {

      final response = await http.post(
      Uri.parse('https://api.openai.com/v1/threads'), 
      headers: {
        'Content-Type': 'application/json',
        'OpenAI-Beta': 'assistants=v1',
        'Authorization': 'Bearer $api_key', 
        
      },
      body: null,
    );
    if (response.statusCode == 200) {
      Map<String, dynamic> data = json.decode(utf8.decode(response.bodyBytes));
      thread_id = data['id'];
      return thread_id;

    } else {
      throw Exception('Failed to load response');
    }
  }

  Future<String> _createMessage(String message) async {
      final response = await http.post(
      Uri.parse('https://api.openai.com/v1/threads/$thread_id/messages'), 
      headers: {
        'Content-Type': 'application/json',
        'OpenAI-Beta': 'assistants=v1',
        'Authorization': 'Bearer $api_key', 
      },
      body: json.encode({
        'role':'user',
        'content':message,
      }),
    );

    if (response.statusCode == 200) {
      Map<String, dynamic> data = json.decode(utf8.decode(response.bodyBytes));
      return data['id'];

    } else {
      throw Exception('Failed to load response');
    }
  }

  Future<String> _createRun()async{
      final response = await http.post(
      Uri.parse('https://api.openai.com/v1/threads/$thread_id/runs'), 
      headers: {
        'Content-Type': 'application/json',
        'OpenAI-Beta': 'assistants=v1',
        'Authorization': 'Bearer $api_key', 
        
      },
      body: json.encode({
        'assistant_id':assistant_id,
      }),
    );

    if (response.statusCode == 200) {
      Map<String, dynamic> data = json.decode(utf8.decode(response.bodyBytes));
  
      return data['id'];
    } else {
      throw Exception('Failed to load response');
    }

 }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Chatbot App'),
      ),
      body: Column(
        children: <Widget>[
          Expanded(
            child: ListView.builder(
              itemCount: _messages.length,
              itemBuilder: (context, index) {
                return ListTile(
                  title: Text(_messages[index]['text']),
                  leading: _messages[index]['user'] ? const Icon(Icons.face) : const Icon(Icons.android),
                );
              },
            ),
          ),
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: Row(
              children: <Widget>[
                Expanded(
                  child: TextField(
                    controller: _controller,
                    decoration: const InputDecoration(
                      hintText: 'Enter your message...',
                    ),
                  ),
                ),
                IconButton(
                  icon: const Icon(Icons.send),
                  onPressed: _sendMessage,
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}