# Amplify Flutter Workshop

## Prerequisites

### CLI 설치와 업데이트
* Update the AWS CLI

pip install --user --upgrade awscli

* Install the AWS Amplify CLI

npm install -g @aws-amplify/cli

* Install and use Node.js v12.x (to match AWS Lambda)

nvm ls-remote | grep v12
nvm install v12.11.0
nvm alias default v12.11.0

* Flutter version 2.0.0 or higher (make sure you are using a stable version of flutter)

### 기본 region 설정하기
가장 좋은 방법은 인프라를 고객과 가까운 지역에 구성하는 것입니다. (Amplify는 서울 리전도 지원합니다.)

**AWS config file이 없다면 Workshop 진행의 편의를 위해서 생성**합니다. 원하는 리전을 선택해서 하나만 진행하시면 됩니다.

* us-east-1(버지니아)를 사용하는 경우

cat <<END > ~/.aws/config
[default]
region=us-east-1
END

* ap-northeast-2(한국)를 사용하는 경우

cat <<END > ~/.aws/config
[default]
region=ap-northeast-2
END

AWS Amplify CLI는 모바일과 웹 어플리케이션을 개발을 심플하게 해주는 강력한 기능들을 제공하는 툴체인 입니다. 위의 단계에서는 설치만 진행했기 때문에 설정 단계가 추가적으로 필요합니다. AWS Amplify CLI는 ~/.aws/config을 찾아 작업할 Region 정보를 판별합니다. Cloud9은 유효한 Administrator credentials이 ~/.aws/credentials 파일안에 있는지 확인만 할 뿐 ~/.aws/config을 생성하지 않습니다.

## Flutter 프로젝트

* Flutter CLI를 이용하여 새 프로젝트를 시작합니다.

flutter create amplified_todo

### 애플리케이션에 Amplify를 추가합니다.
Amplify for Flutter는 pub.dev를 통해 배포됩니다.

프로젝트 루트 디렉터리에서 **pubspec.yaml**을 찾아 수정하고 Amplify 플러그인을 프로젝트 종속성에 추가합니다.

 environment:
   sdk: ">=2.12.0 <3.0.0"

 dependencies:
  flutter:
    sdk: flutter

  amplify_flutter: ^0.2.0
  amplify_auth_cognito: ^0.2.0
  amplify_analytics_pinpoint: ^0.2.0
  amplify_storage_s3: ^0.2.0
  
  file_picker: ^3.0.0-nullsafety.2
  

다음 명령을 실행하여 종속성을 설치합니다. 개발 환경에 따라 IDE를 통해 이 단계를 수행할 수 있습니다.(또는 자동으로 수행될 수도 있음)

flutter pub get 

### iOS 플랫폼 업데이트

프로젝트 루트에서 **ios/** 디렉터리로 이동하고 선택한 텍스트 편집기를 사용하여 **Podfile**을 수정하고 대상 iOS 플랫폼을 13.0 이상으로 업데이트합니다.

platform :ios, '13.0'

### Android SDK 버전 업데이트

프로젝트 루트에서 **android/app/** 디렉터리로 이동하고 원하는 텍스트 편집기를 사용하여 **build.gradle**을 수정하고 대상 Android SDK 버전을 21 이상으로 업데이트합니다.

minSdkVersion 21

축하합니다🎉 Amplify로 구축을 시작할 준비가 되었습니다.

---

## Amplify CLI를 이용하여 백앤드 프로비저닝
백엔드에서 리소스 프로비저닝을 시작하려면 디렉터리를 프로젝트 디렉터리로 변경하고 amplify init를 실행합니다.

# in future, make sure you have Amplify CLI v4.28 and above for Flutter support
# npm install -g @aws-amplify/cli
amplify init

메시지가 표시되면 다음을 입력합니다.

? Enter a name for the environment
    `dev`
? Choose your default editor:
    `IntelliJ IDEA`
? Choose the type of app that you're building: 
    'flutter'
? Where do you want to store your configuration file? 
    ./lib/
? Do you want to use an AWS profile?
    `Yes`
? Please choose the profile you want to use
    `default`

amplifyconfiguration.dart.
amplify init를 성공적으로 실행하면 ./lib/에 amplifyconfiguration.dart라는 구성 파일이 생성된 것을 볼 수 있습니다.

이 파일은 Amplify 라이브러리가 프로비저닝된 백엔드 리소스에 도달하는 방법을 알 수 있도록 애플리케이션에 번들로 제공됩니다.

:::warning

:information_source: 팁! iOS 오류 해결
* iOS에서 테스트를 하는 동안 아래와 같은 오류가 발생하였다면,

Error running pod install
Error launching application on iPhone 11.

* 다음과 같은 명령을 통해서 해결이 가능합니다.

cd ios && pod update

:::

---

## Amplify
* 이 프로젝트에서 사용할 Amplify 기능들을 추가합니다.
* Amplify 카테고리 추가(이 예에서는 기본값 선택)

amplify add auth
amplify add analytics
amplify add storage

* 클라우드에 변경 사항을 푸시하여 백엔드 리소스를 프로비저닝합니다.

amplify push

---
## lib/main.dart
* Amplify 패키지 추가합니다.

import 'package:amplify_flutter/amplify.dart';
import 'package:amplify_analytics_pinpoint/amplify_analytics_pinpoint.dart';
import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_storage_s3/amplify_storage_s3.dart';
import 'package:flutter/material.dart';

import 'amplifyconfiguration.dart';

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

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  bool _isAmplifyConfigured = false;

  @override
  initState() {
    super.initState();
    _initAmplifyFlutter();
  }

  void _initAmplifyFlutter() async {
    Amplify.addPlugins(
        [AmplifyAuthCognito(), AmplifyStorageS3(), AmplifyAnalyticsPinpoint()]);

    // Initialize AmplifyFlutter
    try {
      await Amplify.configure(amplifyconfig);
      print('Successfully configured Amplify 🎉');
    } on AmplifyAlreadyConfiguredException {
      print(
          "Amplify was already configured. Looks like app restarted on android.");
    }

    setState(() {
      _isAmplifyConfigured = true;
    });
  }

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Amplify App',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text("Hello Flutter App"),
        ),
        body: new Center(
          child: new Text("Hello Flutter"),
        ),
      ),
    );
  }
}

### landing / loading page
* /lib/Pages 폴더를 생성합니다.

* Amplify SDK 가 로딩되지 않았을때, 표시해줄 페이지를 만듭니다.
* /lib/Pages/LoadingPage.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

class LoadingPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Landing Page")),
      body:
          Center(child: Text("Please Wait.  Configuring Amplify Flutter SDK")),
    );
  }
}

* 첫 페이지를 작성합니다.
* /lib/Pages/LandingPage.dart

import 'package:flutter/material.dart';

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

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

class _LandingPageState extends State<LandingPage> {
  Future<Null> _showDialogForResult(
      String text, Function onSuccess, Widget dialogWidget) async {
    bool result = await showDialog(
        context: context,
        builder: (BuildContext context) {
          return new SimpleDialog(title: Text(text), children: [
            dialogWidget,
            ElevatedButton(
              child: const Text("Cancel"),
              onPressed: () {
                Navigator.pop(context, false);
              },
            ),
          ]);
        });

    if (result) onSuccess();
  }

  // dialogWidget must return true or false
  Widget openDialogButton(
      String text, Function onSuccess, Widget dialogWidget) {
    return ElevatedButton(
        child: Text(text),
        onPressed: () {
          _showDialogForResult(text, onSuccess, dialogWidget);
        });
  }

  void onSignInSuccess() {
    print('Sign in Success');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Landing Page"),
        ),
        body: Center(
            child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            Center(child: Text("This is a Landing Page!")),
          ],
        )));
  }
}

* main.dart파일에서 import를 추가 합니다.

import 'Pages/LoadingPage.dart';
import 'Pages/LandingPage.dart';

* _display 함수를 추가합니다.

  Widget _display() {
    if (_isAmplifyConfigured) {
      return LandingPage();
    } else {
      return LoadingPage();
    }
  }

* build 함수를 업데이트 합니다.

@override
Widget build(BuildContext context) {
    return MaterialApp(
        title: 'Flutter Amplify App',
        theme: ThemeData(
          primarySwatch: Colors.blue,
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: _display());
  }

---
## 뷰 작성
* 뷰를 위한 폴더를 생성합니다. : /lib/Views

### 오류 표기를 위한 페이지 작성
* 오류 페이지를 작성합니다. /lib/Views/ErrorView.dart

import 'package:flutter/material.dart';

class ErrorView extends StatelessWidget {
  final String error;

  ErrorView(this.error);

  @override
  Widget build(BuildContext context) {
    if (error.isNotEmpty) {
      return Column(children: <Widget>[
        Text('Error: $error',
            textAlign: TextAlign.center,
            overflow: TextOverflow.visible,
            style: TextStyle(fontWeight: FontWeight.bold)),
      ]);
    } else {
      return Container();
    }
  }
}

### 회원 가입과 로그인 뷰 만들기
* 회원 가입 뷰를 생성합니다.
* /lib/Views/SignUpView.dart

import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_flutter/amplify.dart';
import 'package:flutter/material.dart';
import 'ErrorView.dart';

class SignUpView extends StatefulWidget {
  @override
  _SignUpViewState createState() => _SignUpViewState();
}

class _SignUpViewState extends State<SignUpView> {
  final usernameController = TextEditingController();
  final passwordController = TextEditingController();
  final emailController = TextEditingController();
  final confirmationCodeController = TextEditingController();

  String _signUpError = "";
  bool _isSignedUp = false;

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

  void _signUp() async {
    setState(() {
      _signUpError = "";
    });

    Map<String, String> userAttributes = {
      "email": emailController.text,
    };
    try {
      SignUpResult res = await Amplify.Auth.signUp(
          username: usernameController.text.trim(),
          password: passwordController.text.trim(),
          options: CognitoSignUpOptions(userAttributes: userAttributes));

      setState(() {
        _isSignedUp = true;
      });
    } on AuthException catch (error) {
      _setError(error);
    }
  }

  void _confirmSignUp() async {
    setState(() {
      _signUpError = "";
    });

    try {
      SignUpResult res = await Amplify.Auth.confirmSignUp(
          username: usernameController.text.trim(),
          confirmationCode: confirmationCodeController.text.trim());
      Navigator.pop(context, true);
    } on AuthException catch (error) {
      _setError(error);
    }
  }

  void _setError(AuthException error) {
    setState(() {
      _signUpError = error.message;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: <Widget>[
        Expanded(
          // wrap your Column in Expanded
          child: Padding(
            padding: EdgeInsets.all(10.0),
            child: Column(
              children: [
                Visibility(
                  visible: !_isSignedUp,
                  child: Column(children: [
                    TextFormField(
                      controller: usernameController,
                      decoration: const InputDecoration(
                        icon: Icon(Icons.person),
                        hintText: 'Username',
                        labelText: 'Username *',
                      ),
                    ),
                    TextFormField(
                      obscureText: true,
                      controller: passwordController,
                      decoration: const InputDecoration(
                        icon: Icon(Icons.lock),
                        hintText: 'Password',
                        labelText: 'Password *',
                      ),
                    ),
                    TextFormField(
                      controller: emailController,
                      decoration: const InputDecoration(
                        icon: Icon(Icons.email),
                        hintText: 'Email',
                        labelText: 'Email *',
                      ),
                    ),
                    ElevatedButton(
                      onPressed: _signUp,
                      child: const Text('Sign Up'),
                    ),
                  ]),
                ),
                Visibility(
                    visible: _isSignedUp,
                    child: Column(children: [
                      TextFormField(
                          controller: confirmationCodeController,
                          decoration: const InputDecoration(
                            icon: Icon(Icons.confirmation_number),
                            hintText: 'The code we sent you',
                            labelText: 'Confirmation Code *',
                          )),
                      ElevatedButton(
                        onPressed: _confirmSignUp,
                        child: const Text('Confirm Sign Up'),
                      ),
                    ])),
                const Padding(padding: EdgeInsets.all(10.0)),
                ErrorView(_signUpError)
              ],
            ),
          ),
        ),
      ],
    );
  }
}

* 로그인 뷰를 생성합니다.
* /lib/Views/SignInView.dart

import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_flutter/amplify.dart';
import 'package:flutter/material.dart';

import 'ErrorView.dart';

class SignInView extends StatefulWidget {
  @override
  _SignInViewState createState() => _SignInViewState();
}

class _SignInViewState extends State<SignInView> {
  final usernameController = TextEditingController();
  final passwordController = TextEditingController();

  String _signUpError = "";

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

  void _signIn() async {
    // Sign out before in case a user is already signed in
    // If a user is already signed in - Amplify.Auth.signIn will throw an exception
    try {
      await Amplify.Auth.signOut();
    } on AuthException catch (e) {
      print(e);
    }

    try {
      SignInResult res = await Amplify.Auth.signIn(
          username: usernameController.text.trim(),
          password: passwordController.text.trim());
      Navigator.pop(context, true);
    } on AuthException catch (e) {
      setState(() {
        _signUpError = e.message;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: <Widget>[
        Expanded(
          // wrap your Column in Expanded
          child: Padding(
            padding: EdgeInsets.all(10.0),
            child: Column(
              children: [
                TextFormField(
                  controller: usernameController,
                  decoration: const InputDecoration(
                    icon: Icon(Icons.person),
                    hintText: 'Enter your username',
                    labelText: 'Username *',
                  ),
                ),
                TextFormField(
                  obscureText: true,
                  controller: passwordController,
                  decoration: const InputDecoration(
                    icon: Icon(Icons.lock),
                    hintText: 'Enter your password',
                    labelText: 'Password *',
                  ),
                ),
                const Padding(padding: EdgeInsets.all(10.0)),
                ElevatedButton(
                  onPressed: _signIn,
                  child: const Text('Sign In'),
                ),
                ErrorView(_signUpError)
              ],
            ),
          ),
        ),
      ],
    );
  }
}

* 로그인과 회원가입 기능(버튼)을 추가합니다.
* /lib/Pages/LandingPage.dart

import '../Views/SignInView.dart';
import '../Views/SignUpView.dart';


        body: Center(
            child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            openDialogButton("Sign In", onSignInSuccess, SignInView()),
            openDialogButton(
                "Sign Up", () => {print("sign up success")}, SignUpView())
          ],
        )));

---

### MainPage
* /lib/Pages/MainPage.dart 파일을 생성합니다.

import 'package:amplify_flutter/amplify.dart';
import 'package:amplify_storage_s3/amplify_storage_s3.dart';
import 'package:flutter/material.dart';

class MainPage extends StatefulWidget {
  @override
  _MainPageState createState() => _MainPageState();
}

class _MainPageState extends State<MainPage> {
  List<String> itemKeys = [];

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

  void _loadImages() async {
    try {
      print('In list');
      S3ListOptions options =
          S3ListOptions(accessLevel: StorageAccessLevel.guest);
      ListResult result = await Amplify.Storage.list(options: options);

      var newList = itemKeys.toList();
      for (StorageItem item in result.items) {
        newList.add(item.key);
      }

      setState(() {
        itemKeys = newList;
      });
    } catch (e) {
      print('List Err: ' + e.toString());
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          title: Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [Text("Main Page")])),
      body: new Center(
        child: new Text("Hello Flutter. This is main page."),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

* 로그인후 페이지 이동
* /lib/Pages/LandingPage.dart

import 'MainPage.dart';

void onSignInSuccess() {
    Navigator.pushAndRemoveUntil(context,
        MaterialPageRoute(builder: (context) => MainPage()), (route) => false);
  }
  
...

* 사용자 로그아웃을 위한 뷰를 생성합니다.
* /lib/Views/UserView.dart

import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_flutter/amplify.dart';
import 'package:flutter/material.dart';
import '../Pages/LandingPage.dart';

class UserView extends StatefulWidget {
  @override
  _UserProfileState createState() => _UserProfileState();
}

class _UserProfileState extends State<UserView> {
  @override
  void initState() {
    super.initState();
  }

  void _signOut() async {
    try {
      SignOutResult res = await Amplify.Auth.signOut();

      Navigator.pushAndRemoveUntil(
          context,
          MaterialPageRoute(builder: (context) => LandingPage()),
          (route) => false);
    } on AuthException catch (e) {
      print(e);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: <Widget>[
        ElevatedButton(onPressed: _signOut, child: const Text("Log Out")),
      ],
    );
  }
}

* /lib/Pages/MainPage.dart 파일을 생성합니다.

import '../Views/UserView.dart';

...
      appBar: AppBar(
          title: Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [Text("Main Page"), UserView()])),

---
## 업로드된 이미지 보기 기능 추가
### 이미지 보기 뷰 추가
* /lib/Views/ImageLineItem.dart

import 'package:flutter/material.dart';

class ImageLineItem extends StatelessWidget {
  final String storageKey;

  const ImageLineItem({
    Key? key,
    required this.storageKey,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Padding(
        padding: EdgeInsets.all(5.0),
        child: Row(mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [
          Text(storageKey),
          Spacer(),
        ]));
  }
}

### 메인 페이지에 기능 추가
* /lib/Pages/MainPage.dart 파일을 수정합니다.
* 업로드 이미지 보기

import '../Views/ImageLineItem.dart';


    body: ListView.builder(
          itemCount: itemKeys.length,
          itemBuilder: (context, index) {
            return ImageLineItem(storageKey: itemKeys[index]);
          }),
          

---
## 이미지 업로드 기능 추가
### 이미지 업로드 뷰 추가
* /lib/Views/ImageUploader.dart

import 'package:flutter/material.dart';
import 'dart:io';
import 'package:file_picker/file_picker.dart';
import 'package:amplify_flutter/amplify.dart';
import 'package:amplify_storage_s3/amplify_storage_s3.dart';

class ImageUploader extends StatelessWidget {
  void _upload(BuildContext context) async {
    List<PlatformFile>? _paths;
    try {
      print('In upload');
      // Uploading the file with options
      _paths =
          (await FilePicker.platform.pickFiles(type: FileType.image))?.files;

      File local = File(_paths!.single.path!);
      local.existsSync();
      final key = new DateTime.now().toString();
      Map<String, String> metadata = <String, String>{};
      metadata['name'] = 'filename';
      metadata['desc'] = 'A test file';
      S3UploadFileOptions options = S3UploadFileOptions(
          accessLevel: StorageAccessLevel.guest, metadata: metadata);
      UploadFileResult result = await Amplify.Storage.uploadFile(
          key: key, local: local, options: options);

      print('File uploaded.  Key: ' + result.key);
      Navigator.pop(context, result.key);
    } catch (e) {
      print('UploadFile Err: ' + e.toString());
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(children: [
      ElevatedButton(
        child: const Text("Upload Image"),
        onPressed: () {
          _upload(context);
        },
      )
    ]);
  }
}

### 메인 페이지에 기능 추가
* /lib/Pages/MainPage.dart 파일을 수정합니다.
* 이미지 업로드 기능 추가

import '../Views/ImageUploader.dart';

...

  void _showImageUploader() async {
    try {
      String key;
      key = await showDialog(
          context: context,
          builder: (BuildContext context) {
            return new SimpleDialog(
                title: Text("Upload Image"), children: [ImageUploader()]);
          });

      if (key.isNotEmpty) {
        var newList = itemKeys.toList();
        newList.add(key);

        setState(() {
          itemKeys = newList;
        });
      }
    } catch (e) {
      print('Dialog Err: ' + e.toString());
    }
  }
  
  ...
  
     floatingActionButton: FloatingActionButton(
        onPressed: () {
          _showImageUploader();
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),

---
## 이미지 보기 기능 추가
### 이미지 보기 뷰 추가
* /lib/Views/ImagePreview.dart

import 'package:amplify_analytics_pinpoint/amplify_analytics_pinpoint.dart';
import 'package:amplify_flutter/amplify.dart';
import 'package:amplify_storage_s3/amplify_storage_s3.dart';
import 'package:flutter/material.dart';

class ImagePreview extends StatefulWidget {
  final String storageKey;

  ImagePreview({Key? key, required this.storageKey}) : super(key: key);

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

class _ImagePreviewState extends State<ImagePreview> {
  String _imageURL = '';

  @override
  void initState() {
    super.initState();
    _getUrl(widget.storageKey);
  }

  void _getUrl(String storageKey) async {
    try {
      print('In getUrl');
      String key = storageKey;
      S3GetUrlOptions options = S3GetUrlOptions(
          accessLevel: StorageAccessLevel.guest, expires: 10000);
      GetUrlResult result =
          await Amplify.Storage.getUrl(key: key, options: options);

      setState(() {
        _imageURL = result.url;
      });

      print('URL: ' + _imageURL);
      AnalyticsEvent event = AnalyticsEvent("image_url_retrieved");
      event.properties.addStringProperty("file_key", storageKey);
      Amplify.Analytics.recordEvent(event: event);
    } catch (e) {
      print('GetUrl Err: ' + e.toString());
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(children: [
      //Image(image: AssetImage('images/image.png')),
      Center(child: Image.network(_imageURL))
    ]);
  }
}

### 이미지 리스트 뷰에 기능 추가
* /lib/Views/ImageLineItem.dart

import 'ImagePreview.dart';

...

return Padding(
        padding: EdgeInsets.all(5.0),
        child: Row(mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [
          Text(storageKey),
          Spacer(),
          ElevatedButton(
              child: const Text("open"),
              onPressed: () => {
                    showDialog(
                        context: context,
                        builder: (BuildContext context) {
                          return new SimpleDialog(
                              title: Text(storageKey),
                              children: [ImagePreview(storageKey: storageKey)]);
                        })
                  })
        ]));

---

## References
* https://github.com/aws-amplify/amplify-flutter/tree/main/example
* https://docs.amplify.aws/start/q/integration/flutter
* https://docs.amplify.aws/lib/q/platform/flutter
* https://aws.amazon.com/ko/blogs/korea/amplify-flutter-is-now-generally-available-build-beautiful-cross-platform-apps/
* https://aws.amazon.com/ko/getting-started/hands-on/build-flutter-app-amplify/