usecasesample2.dart

//Usecase Implementation
class ValidateBillingAndShippingAddressUseCase extends UseCase<
    BillingAndShippingAddressValidationRequest,
    BillingAndShippingAddressValidationResponse> {
  final AddressRespository _addressRespository;

  ValidateBillingAndShippingAddressUseCase(this._addressRespository);

  @override
  Stream<BillingAndShippingAddressValidationResponse> buildUseCase(
      BillingAndShippingAddressValidationRequest param) {
    return _addressRespository.validate(param).asStream();
  }
}

//Usecase Implementation
class PostShippingAndValidationBillingShippingAddress extends UseCase<
    PostShippingAndValidationAddressRequest,
    BillingAndShippingAddressValidationResponse> {
  final PostShippingInfoUseCase _postShippingInfoUseCase;
  final ValidateBillingAndShippingAddressUseCase
      _billingAndShippingAddressUseCase;

  PostShippingAndValidationBillingShippingAddress(
      this._postShippingInfoUseCase, this._billingAndShippingAddressUseCase);

  @override
  Stream<BillingAndShippingAddressValidationResponse> buildUseCase(
      PostShippingAndValidationAddressRequest param) {
    return _postShippingInfoUseCase
        .buildUseCase(param._shippingInfoRequest)
        .flatMap((shippingResponse) => _billingAndShippingAddressUseCase
            .buildUseCase(param._addressValidationRequest));
  }
}

//Usecase invocation from presentation layer
PostShippingAndValidationBillingShippingAddress(
          PostShippingInfoUseCase(MockedShippingInfoRepository()),
          ValidateBillingAndShippingAddressUseCase(
              MockedAddressValidationRepository()))
      .execute(
          PostShippingAndValidationAddressRequest(ShippingInfoRequest(),
              BillingAndShippingAddressValidationRequest()),
          (result) {
            //TODO Display result
          },
          (errorMessage) {
            //TODO Display error
          });

//Usecase Implementation
class PostBillingShippingInfoAndValidateAddressUseCase extends UseCase<
    BillingShippingInfoRequest, BillingAndShippingAddressValidationResponse> {
  final PostBillingInfoUseCase _billingInfoUseCase;
  final PostShippingInfoUseCase _shippingInfoUseCase;
  final ValidateBillingAndShippingAddressUseCase
      _billingAndShippingAddressValidationUseCase;

  PostBillingShippingInfoAndValidateAddressUseCase(
    this._billingInfoUseCase,
    this._shippingInfoUseCase,
    this._billingAndShippingAddressValidationUseCase,
  );

  @override
  Stream<BillingAndShippingAddressValidationResponse> buildUseCase(
      BillingShippingInfoRequest param) {
    return Rx.zip2(
            _billingInfoUseCase.buildUseCase(param.billingInfoRequest),
            _shippingInfoUseCase.buildUseCase(param.shippingInfoRequest),
            (BillingInfoResponse billingResult,
                    ShippingInfoResponse shippingResult) =>
                BillingShippinInfoResponse.from(billingResult, shippingResult))
        .flatMap((billingShippingResult) =>
            _billingAndShippingAddressValidationUseCase
                .buildUseCase(BillingAndShippingAddressValidationRequest()));
  }
}

//Usecase invocation from presentation layer
  PostBillingShippingInfoAndValidateAddressUseCase(
          PostBillingAndShippingInfoUseCase(
              PostBillingInfoUseCase(MockedBillingInfoRepository()),
              PostShippingInfoUseCase(MockedShippingInfoRepository())),
          ValidateBillingAndShippingAddressUseCase(
              MockedAddressValidationRepository()))
      .execute(
          BillingShippingInfoRequest(
              BillingInfoRequest(), ShippingInfoRequest()), (result) {
    //TODO Display result
  }, (errorMessage) {
    //TODO Display error
  });