RecyclerView_and_cycle.kt

fun Observable<Int>.foo(userApp: UserAppService): Pair<Observable<UiModel>, Observable<Boolean>> {
  val shouldShowLoading = BehaviorSubject.createDefault<Boolean>(false).toSerialized()

  var isLoading = false
  var hasLoaded = false
  var page = 1

  val uiModel = this
      .filter { !hasLoaded && !isLoading }
      .doOnNext { _ ->
        isLoading = true
        if (page != 1) shouldShowLoading.onNext(true)
      }
      .flatMap(
          { _ ->
            userApp.getAllUsers(++page, 20)
                .doOnEach { shouldShowLoading.onNext(false) }
                .delay(2, TimeUnit.SECONDS)
                .subscribeOnIo()
                .observeOnMain()
          },
          { t1, t2 -> page to t2 })
      .doOnNext { (page, _) ->
        isLoading = false
        if (page != 1) shouldShowLoading.onNext(false)
      }
      .map { (page, userList) ->

        if (userList.isEmpty()) {
          hasLoaded = true
        }

        if (page == 1 && userList.isEmpty()) {
          EmptyModel
        } else {
          DataModel(userList, userList.isEmpty())
        }
      }
      .onErrorReturn { ErrorModel }
      .startWith(LoadingModel)

  return uiModel to shouldShowLoading.hide()
}

sealed class UiModel
object EmptyModel : UiModel()
object ErrorModel : UiModel()
object LoadingModel : UiModel()
data class DataModel(val data: List<User>, val hasLoaded: Boolean) : UiModel()