SampleMvvmViewState.kt

data class ViewState(
    val loginButtonEnabled: ObservableBoolean = ObservableBoolean(false)
) : ViewStateType

sealed class Mutation : MutationType {
    class LoginButtonEnabled(val enabled: Boolean) : Mutation()
}

sealed class Action : ActionType {
    object LoginButtonClicks : Action()
    data class EmailInputs(val inputs: String) : Action()
    data class PasswordInputs(val inputs: String) : Action()
    data class AccountItemAction(val action: AccountItemAction) : Action()
}

interface MainViewModel {

    class ViewModel(application: Application) : BaseViewModel<ViewState>(application) {

        init {
            val emailAndPassword = Observables.combineLatest(
                actions().filterType<Action.EmailInputs>()
                    .map { it.inputs },
                actions().filterType<Action.PasswordInputs>()
                    .map { it.inputs }
            )

            // test
            val loginButtonClicks = actions().filterType<Action.LoginButtonClicks>()
                .share()

            act(Action.LoginButtonClicks)

            // handle success and failure with notification
            val loginRequestNotification = loginButtonClicks
                .withLatestFrom(emailAndPassword) { _, pair -> pair }
                .switchMap { login(it.first, it.second) }
                .materialize()

            // mutate login button enabled state
            emailAndPassword
                .map { !it.first.isNullOrEmpty() && !it.second.isNullOrEmpty() }
                .map { enabled -> Mutation.LoginButtonEnabled(enabled) }
                .autoDispose()
                .subscribe { mutate(it) }
        }

        private fun login(email: String, password: String): Observable<Unit> {
            return Observable.empty()
        }

        override fun reduce(mutation: MutationType, viewState: ViewState): ViewState {
            return when (mutation) {
                is Mutation.LoginButtonEnabled -> {
                    viewState.apply {
                        this.loginButtonEnabled.set(mutation.enabled)
                    }
                }
                else -> viewState
            }
        }
    }
}