@Transactional
@Service
public class ChannelCreatedService {

  private MethodsClient slackClient;
  private ChannelRepository channels;

  public ChannelCreatedService(final MethodsClient slackClient, final ChannelRepository channels) {
    this.slackClient = slackClient;
    this.channels = channels;
  }

  public Channel execute(final String channelSlackId) {
    try {
      // slack api를 호출하는 부분
      Conversation conversation = slackClient
        .conversationsInfo(request -> request.channel(channelSlackId))
        .getChannel();

      // slack의 response를 우리 도메인인 channel 형태로 변환
      Channel channel = toChannel(conversation);

      // channel을 저장하고 return
      return channels.save(channel);

    } catch (IOException | SlackApiException e) { // slack api 호출로 인해 발생할 수 있는 exception
      throw new SlackApiCallException();
    }
  }
}

@Transactional
@Service
public class ChannelCreatedService {

  private CallSlackApi slackClient;
  private ChannelRepository channels;

  public ChannelCreatedService(final CallSlackApi slackClient, final ChannelRepository channels) {
    this.slackClient = slackClient;
    this.channels = channels;
  }

  public Channel execute(final String channelSlackId) {
    Channel channel = slackClient.callChannel(channelSlackId);
    return channels.save(channel);
  }
}

@Component
public class CallSlackApi {

  private final MethodsClient methodsClient;

  public CallSlackApi(final MethodsClient methodsClient) {
    this.methodsClient = methodsClient;
  }

  public Channel callChannel(final String channelSlackId) {
    try {
      // `Slack 라이브러리`를 호출
      Conversation conversation = methodsClient.conversationsInfo(
          request -> request.channel(channelSlackId))
        .getChannel();

      // 결과값을 우리가 사용하는 객체 형태로 변경
      return new Channel(conversation.getId(), conversation.getName());

    } catch (IOException | SlackApiException e) {
      throw new SlackApiCallException();
    }
  }
}

public interface ExternalClient {
  Channel callChannel(String channelSlackId);
}

@Component
public class SlackClient implements ExternalClient {

  private MethodsClient methodsClient;

  public SlackClient(final MethodsClient methodsClient) {
    this.methodsClient = slackClient;
  }

  public Channel callChannel(final String channelSlackId) {
    try {
      Conversation conversation = methodsClient.conversationsInfo(
          request -> request.channel(channelSlackId))
        .getChannel();

      return new Channel(conversation.getId(), conversation.getName());

    } catch (IOException | SlackApiException e) {
      throw new SlackApiCallException();
    }
  }
}

@Primary // SlackClient 보다 우선 순위가 높은 bean으로 등록하기 위해 붙였다.
@Component
public class FakeClient implements ExternalClient {

  private List<Channel> channels = List.of( ...); // 채널 데이터 초기화

  @Override
  public Channel callChannel(final String channelSlackId) {
    return channels.stream()
      .filter(it -> it.isSameSlackId(channelSlackId))
      .findAny()
      .orElseThrow(() -> new SlackApiCallException());
  }
}

@Test
void execute() {
  // given
  Workspace workspace = workspaces.save(WorkspaceFixture.JUPJUP.create());
  Channel channel = ChannelFixture.QNA.create(workspace);
  String request = createRequest(channel);

  given(slackClient.conversationsInfo((RequestConfigurator<ConversationsInfoRequestBuilder>) any()))
    .willReturn(setUpChannelMockData(channel));

  // when
  channelCreatedService.execute(request);

  // then
  Optional<Channel> actual = channels.findBySlackId(channel.getSlackId());
  assertThat(actual).isNotEmpty();
}

private ConversationsInfoResponse setUpChannelMockData(final Channel channel) {
  Conversation conversation = new Conversation();
  conversation.setId(channel.getSlackId());
  conversation.setName(channel.getName());

  ConversationsInfoResponse conversationsInfoResponse = new ConversationsInfoResponse();
  conversationsInfoResponse.setChannel(conversation);
  conversationsInfoResponse.setOk(true);

  return conversationsInfoResponse;
}

@Test
void execute() {
  // given
  Workspace workspace = workspaces.save(WorkspaceFixture.JUPJUP.create());
  Channel channel = ChannelFixture.QNA.create(workspace);
  String request = createRequest(channel);

  // when
  channelCreatedService.execute(request);

  // then
  Optional<Channel> actual = channels.findBySlackId(channel.getSlackId());
  assertThat(actual).isNotEmpty();
}