bot_service.dart

import 'dart:convert';
import 'dart:developer';

import 'package:amazon_cognito_identity_dart_2/sig_v4.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:sigv4/sigv4.dart';

class BotService {
  Map<String,dynamic> result;
  String botName= "<NAME_OF_BOT>";
  String kAccessKeyId = '<ACCESS_KEY>';
  String kSecretAccessKey = '<SECRET_ACCESS_KEY>';
  String botAlias= "<BOT_ALIAS>";
  String botAWSRegion= "<AWS_LEX_REGION>";

  Future<Map<String,dynamic>> callBot(String message) async {
    var response;

    String requestUrl= "https://runtime.lex."+botAWSRegion+".amazonaws.com/bot/"+botName+"/alias/"+botAlias+"/user/1234/text";

    Sigv4Client client = Sigv4Client(
      region: botAWSRegion,
      serviceName: 'lex',
      defaultContentType: 'application/json; charset=utf-8',
      keyId: kAccessKeyId,
      accessKey: kSecretAccessKey,
    );

    final request = client.request(
     requestUrl,
      method: 'POST',
      body: jsonEncode({'inputText': message}),
    );

    response = await http.post(request.url,
        headers: request.headers, body: request.body);
    result = jsonDecode(response.body);
    return result;
  }
}

chat.dart

import 'dart:developer';

import 'package:flutter/material.dart';
import 'package:flutter_chat_ui/flutter_chat_ui.dart';
import 'package:flutter_chat_types/flutter_chat_types.dart' as types;
import 'package:uuid/uuid.dart';

import './bot_service.dart';

class BotScreen extends StatefulWidget {
  const BotScreen({Key? key}) : super(key: key);

  @override
  _BotScreenState createState() => _BotScreenState();
}

class _BotScreenState extends State<BotScreen> {
  List<types.Message> messages=[];
  final _user = const types.User(id: '1234556');
  final _bot = const types.User(id: "123");
//id of bot and user doesn't matter here as we have only pair interaction

  BotService _botService = BotService();

  @override
  void initState() {
    super.initState();
    _loadMessages();
  }

  void _addMessage(types.Message message) async {
    setState(() {
      messages.insert(0, message);
    });
    log("${message.toJson()["text"]}");
    var data = await _botService.callBot(message.toJson()["text"]);
    log("#####${data['message']}");
    setState(() {
      messages.insert(0, botMessageReply(data['message']));
    });
  }

  types.Message botMessageReply(String message) {
    return types.TextMessage(
      author: _bot,
      createdAt: DateTime.now().millisecondsSinceEpoch,
      id: const Uuid().v4(),
      text: message,
    );
  }

  void _handleSendPressed(types.PartialText message) {
    final textMessage = types.TextMessage(
      author: _user,
      createdAt: DateTime.now().millisecondsSinceEpoch,
      id: const Uuid().v4(),
      text: message.text,
    );
    _addMessage(textMessage);
  }

  void _loadMessages() async {
    List<types.Message> messagesList = [];
    Future.delayed(Duration(milliseconds: 300), () {
      messagesList.add(types.TextMessage(
        author: _bot,
        createdAt: DateTime.now().millisecondsSinceEpoch,
        id: const Uuid().v4(),
        text: "Hello. My name is TUTU- your bot. How can I help you?",
      ));

      setState(() {
        messages = messagesList;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar:AppBar(automaticallyImplyLeading: false,title:Text("BOT"),backgroundColor:Colors.purpleAccent),
      body: Chat(
        messages: messages,
        showUserNames: true,
        onSendPressed: _handleSendPressed,
        user: _user,
      ),
    );
  }
}