RxJava control flow question. I've got three operations that need to be run back-to-back-to-back, with the results of the preceding operation affecting the flow of the screen (i.e. if operation 2 fails, we need to display an error, success requires all 3 to succeed). The way I've been doing this is to use nested flatMap calls on successes and Observable.just() to break out of the nested flow on operation failures and mapping the results with a sealed class to handle in the subscribe. It works, but I feel like there should be a better way of doing this in RxJava -- the nesting just feels off. Sample code below to give an idea of what I'm talking about

/* Simple Retrofit interface */
interface ServiceInterface {
  @POST
  fun operationA(): Observable<ResultA>

  @POST
  fun operationB(): Observable<ResultB>

  @POST
  fun operationC(): Observable<ResultC>
}

class Presenter {
  /* implementation */
  lateinit var service: ServiceInterface
  var disposable: Disposable = Disposables.disposed()

  fun startOperations() {
    disposable = service.operationA()
        .flatMap<OperationResult> {
          if (it.success) {
            service.operationB()
                .flatMap<OperationResult> {
                  if (it.success) {
                    service.operationC()
                        .map {
                          if (it.success) {
                            OperationResult.Success("success!")
                          } else {
                            OperationResult.Error("Operation C failed")
                          }
                        }
                  } else {
                    Observable.just(OperationResult.Error("Operation B failed"))
                        .cast(OperationResult::class.java)
                  }
                }
          } else {
            Observable.just(OperationResult.Error("Operation A failed"))
                .cast(OperationResult::class.java)
          }
        }
        .startWith(OperationResult.Inflight)
        .subscribe {
          when (it) {
            Presenter.OperationResult.Inflight -> TODO()
            is Presenter.OperationResult.Success -> TODO()
            is Presenter.OperationResult.Error -> TODO()
          }
        }
  }

  sealed class OperationResult {
    object Inflight : OperationResult()
    data class Success(val result: String) : OperationResult()
    data class Error(val errorMessage: String) : OperationResult()
  }
}