data class State(
  val isLoading: Boolean = false,
  val value: Int? = null
)

sealed class Effect {
  object ShowError : Effect()
}

sealed class Command {
  object LoadValue : Command()
}

sealed class Event {
  sealed class Ui : Event() {
    object Init : Ui()
    object ReloadClick : Ui()
  }
  sealed class Internal : Event() {
    data class ValueLoadingSuccess(val value: Int) : Internal()
    object ValueLoadingError : Internal()
  }
}

object ValueRepository {
private val random = Random()
fun getValue() = Single.timer(2, TimeUnit.SECONDS)
    .map { random.nextInt() }
    .doOnSuccess { if (it % 3 == 0) error("Simulate unexpected error") }
}

class Actor : Actor<Command, Event> {
override fun execute(command: Command): Observable<Event> = when (command) {
    is Command.LoadNewValue -> ValueRepository.getValue()
        .mapEvents(Internal::ValueLoaded, Internal.ErrorLoadingValue)
}
}

class Reducer : DslReducer<Event, State, Effect, Command>() {
override fun Result.reducer(event: Event) = when (event) {
    is Internal.ValueLoaded -> {
        state { copy(isLoading = false, value = event.value) }
    }
    is Internal.ErrorLoadingValue -> {
        state { copy(isLoading = false) }
        effects { +Effect.ShowError }
    }
    is Ui.Init -> {
        state { copy(isLoading = true) }
        commands { +Command.LoadNewValue }
    }
    is Ui.ClickReload -> {
        state { copy(isLoading = true, value = null) }
        commands { +Command.LoadNewValue }
    }
}
}

fun storeFactory() = ElmStore(
    initialState = State(),
    reducer = MyReducer(),
    actor = MyActor()
).start()

class MainActivity : ElmActivity<Event, Effect, State>() {
override val initEvent: Event = Event.Ui.Init
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    findViewById<Button>(R.id.reload).setOnClickListener {
       store.accept(Event.Ui.ClickReload)
    }
}
override fun createStore() = storeFactory()
override fun render(state: State) {
    findViewById<TextView>(R.id.currentValue).text = when {
        state.isLoading -> "Loading..."
        state.value == null -> "Value = Unknown"
        else -> "Value = ${state.value}"
    }
}
override fun handleEffect(effect: Effect) = when (effect) {
    Effect.ShowError -> Snackbar
        .make(findViewById(R.id.content), "Error!", Snackbar.LENGTH_SHORT)
        .show()
}
}