ExampleComponent.kt

package y2k.rxstateexample.react

import kotlinx.coroutines.experimental.Job
import kotlinx.coroutines.experimental.android.UI
import kotlinx.coroutines.experimental.channels.BroadcastChannel
import kotlinx.coroutines.experimental.launch
import y2k.rxstateexample.common.Service
import y2k.rxstateexample.common.toUser
import y2k.rxstateexample.react.ExampleComponent.Events
import y2k.rxstateexample.react.ExampleComponent.State

class ExampleComponent(private val service: Service) : Component<State, Events>() {

    /** Обработка входящих событий. */
    override fun update(event: Events) {
        when (event) {
            is Events.EmailChanged -> updateState(getState().copy(email = event.value))
            is Events.NameChanged -> updateState(getState().copy(name = event.value))
            is Events.SurnameChanged -> updateState(getState().copy(surname = event.value))
            Events.Clicked -> {
                service.saveUser(getState().toUser())
                updateState(getState())
            }
        }
    }

    private fun updateState(state: State) {
        val emailValid = state.email.contains("@")
        val usersEqual = service.readUser() == state.toUser()
        val newState = state.copy(
            emailValid = emailValid,
            buttonEnabled = emailValid && !usersEqual,
            buttonText = if (usersEqual) "Nothing changed" else "Save changes")
        setState(newState)
    }

    /** Создание начального стейта. */
    override fun getInitState(): State = State(buttonText = "Nothing changed")

    /** Весь "важный" для экрана UI стейт. */
    data class State(
        val email: String = "",
        val name: String = "",
        val surname: String = "",
        val buttonText: String = "",
        val buttonEnabled: Boolean = false,
        val emailValid: Boolean = true)

    /** События приходящие от UI в компонент. */
    sealed class Events {
        class EmailChanged(val value: String) : Events()
        class NameChanged(val value: String) : Events()
        class SurnameChanged(val value: String) : Events()
        object Clicked : Events()
    }
}

// *** *** *** *** *** *** *** *** *** *** *** ***
// Мини фреймворк
// *** *** *** *** *** *** *** *** *** *** *** ***

abstract class Component<TState, TEvent> {
    private var state: TState? = null
    private var callback: ((TState) -> Unit)? = null
    private var subscriptionJob: Job? = null

    abstract fun getInitState(): TState
    abstract fun update(event: TEvent)
    open fun subscription(): Pair<BroadcastChannel<*>, TEvent>? = null

    protected fun setState(state: TState) {
        if (this.state != state) {
            this.state = state
            callback?.invoke(state)
        }
    }

    protected fun getState(): TState {
        if (state == null)
            state = getInitState()
        return state!!
    }

    open fun onStateChanged(callback: ((TState) -> Unit)?) {
        this.callback = callback
        callback?.invoke(getState())
        updateSubscriptions(callback)
    }

    private fun updateSubscriptions(callback: ((TState) -> Unit)?) {
        subscriptionJob?.cancel()
        subscriptionJob = null

        if (callback != null) {
            val (broadcast, updateEvent) = subscription() ?: return
            subscriptionJob = launch(UI) {
                broadcast.openSubscription()
                    .use { s ->
                        while (true) {
                            s.receive()
                            update(updateEvent)
                        }
                    }
            }
        }
    }
}