Redux implementation in Kotlin

appstore1.kt

data class AppState(val searchState: SearchState = SearchState())

class AppStore: Store<AppState>(
  initialState = AppState(),
  reducers = listOf(::reduceSearchState)) {
  
  companion object {
    val instance by lazy {
      AppStore()
    }
  }
  
}

appstore2.kt

data class AppState(val searchState: SearchState = SearchState())

class AppStore: Store<AppState>(
  initialState = AppState(),
  reducers = listOf(::reduceSearchState),
  middleware = listOf(::loggerMiddleware, ::searchMiddleware)) {
  
  companion object {
    val instance by lazy {
      AppStore()
    }
  }
  
}

reduxstore1.kt

abstract class SimpleStore<State>(
  private val initialState: State,
  private val reducers: List<Reducer<State>>): Store<State> {

  private var currentState: State = initialState
  private val subscriptions = arrayListOf<Subscription<State>>()

  override fun getState() = currentState

  override fun dispatch(action: Action) {
    val newState = applyReducers(currentState, action)
    if (newState == currentState) {
      // No change in state
      return
    }
    currentState = newState
    subscriptions.forEach { it(currentState) }
  }

  private fun applyReducers(current: State, action: Action): State {
    var newState = current
    for (reducer in reducers) {
      newState = reducer(newState, action)
    }
    return newState
  }

  override fun subscribe(subscription: Subscription<State>) {
    subscriptions.add(subscription)
    // notify subscription of the current state
    subscription(state)
  }

  override fun unsubscribe(subscription: Subscription<State>) {
    subscriptions.remove(subscription)
  }
}

reduxstore2.kt

abstract class SimpleStore<State>(
  private val initialState: State,
  private val reducers: List<Reducer<State>>): Store<State> {

  private var currentState: State = initialState
  private val subscriptions = arrayListOf<Subscription<State>>()

  private fun dispatch(action: Action) {
    val newState = applyReducers(currentState, action)
    if (newState == currentState) {
      // No change in state
      return
    }
    currentState = newState
    subscriptions.forEach { it(currentState, ::dispatch) }
  }

  override fun subscribe(subscription: Subscription<State>): Unsubscribe {
    subscriptions.add(subscription)
    // notify subscription of the current state
    subscription(state, ::dispatch)
    return { subscriptions.remove(subscription) }
  }
  
  // Rest of the code - reudcers and stuff.
}

reduxstore3.kt

abstract class SimpleStore<State>(
  private val initialState: State,
  private val reducers: List<Reducer<State>>,
  private val middleware: List<Middleware>): Store<State> {

  private var currentState: State = initialState
  private val subscriptions = arrayListOf<Subscription<State>>()

  private fun dispatch(action: Action) {
    val newAction = applyMiddleware(currentState, action)
    val newState = applyReducers(currentState, newAction)
    if (newState == currentState) {
      // No change in state
      return
    }
    currentState = newState
    subscriptions.forEach { it(currentState, ::dispatch) }
  }
  
  private fun applyMiddleware(state: State, action: Action): Action {
    return next(0)(state, action, ::dispatch)
  }
  
  private fun next(index: Int): Next<State> {
    if (index == middleware.size) {
      // Last link of the chain. It just returns the action as is.
      return { _, action, _ -> action }
    }
    
    return { state, action, dispatch -> middleware[index].invoke(state, action, dispatch, next(index+1)) }
  }
  
  // Rest of the code - reudcers and stuff.
}

searchfragment1.kt

class SearchFragment: Fragment() {
  
  override fun onViewCreated(View view) {
    super.onViewCreated(view)
    // .. initialize views
    AppStore.instance.subscribe(::render)
    
    searchButton.setOnClickListener {
      AppStore.instance.dispatch(Seaarch(queryEditText.getText().toString()))
    }
    
    clearButton.setOnClickListener {
      AppStore.instance.dispatch(ClearSearch)
    }
  }
  
  override fun onDestroyView() {
    super.onDestroyView()
    AppStore.instance.unsubscribe(::render)
  }
  
  private fun render(state: AppState) {
    progressbar.show(state.loading)
    clearButton.show(movies.size > 0)
    searchButton.show(!state.loading)
    queryEdittext.setText(state.query)
    adapter.setMovies(movies)
  }
}

searchfragment2.kt

class SearchFragment: Fragment() {
  
  private var dispatch: Dispatch? = null
  private lateinit var unsubscribe: Unsubscribe
  
  override fun onViewCreated(View view) {
    super.onViewCreated(view)
    // .. initialize views
    unsubscribe = AppStore.instance.subscribe(::render)
    
    searchButton.setOnClickListener {
      dispatch?.invoke(Seaarch(queryEditText.getText().toString()))
    }
    
    clearButton.setOnClickListener {
      dispatch?.invoke(ClearSearch)
    }
  }
  
  override fun onDestroyView() {
    super.onDestroyView()
    unsubscribe.invoke()
    dispatch = null
  }
  
  private fun render(state: AppState, dispatch: Dispatch) {
    this.dispatch = dispatch
    // .. rest of the code
  }
}

searchreducer1.kt

data class SearchState(val loading: Boolean = false, val query: String = "", val movies: List<Movie> = listOf())

object ClearSearch: Action
data class Search(val query: String): Action 
data class LoadingSearch(val query: String): Action
data class SearchResultsLoaded(val query: String, val movies: List<Movie>): Action

fun reduceSearchState(state: AppState, action: Action): AppState {
  return when(action) {
    is ClearSearch -> state.copy(searchState = SearchState())
    is LoadingSearch -> state.copy(searchState = SearchState(loading = true, query = action.query))
    is SearchResultsLoaded -> state.copy(searchState = SearchState(query = action.query, loading = false, movies = action.movies))
    else -> state
  }
}