compose-architecture-10

class MviViewModel(
    private val answerService: AnswerService,
) {

    private val coroutineScope = MainScope()

    private val _viewState: MutableStateFlow<ViewState> = MutableStateFlow(ViewState())
    val viewState = _viewState.asStateFlow()

    // See https://proandroiddev.com/android-singleliveevent-redux-with-kotlin-flow-b755c70bb055
    // For why channel > SharedFlow/StateFlow in this case
    private val _oneShotEvents = Channel<OneShotEvent>(Channel.BUFFERED)
    val oneShotEvents = _oneShotEvents.receiveAsFlow()

    fun onAction(uiAction: UiAction) {
        when (uiAction) {
            is UiAction.AnswerConfirmed -> {
                coroutineScope.launch {
                    _viewState.value = _viewState.value.copy(isLoading = true)
                    withContext(Dispatchers.IO) { answerService.save(uiAction.answer) }
                    val text = if (uiAction.answer == "Nacho cheese") {
                        "You've heard too many cheese jokes"
                    } else {
                        "Nacho cheese"
                    }
                    _viewState.value = _viewState.value.copy(textToDisplay = text)
                    _oneShotEvents.send(OneShotEvent.NavigateToResults)
                    _viewState.value = _viewState.value.copy(isLoading = false)
                }
            }
        }
    }

    data class ViewState(
        val isLoading: Boolean = false,
        val textToDisplay: String = "",
    )

    sealed class OneShotEvent {
        object NavigateToResults : OneShotEvent()
    }

    sealed class UiAction {
        class AnswerConfirmed(val answer: String) : UiAction()
    }
}