1 /* 2 * Copyright (C) 2023 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.android.car.customization.tool.domain 18 19 /** 20 * A base class for state machines. 21 * 22 * It provides all the basic properties and functions and also implements the Observer pattern 23 * to make the state machine "reactive". 24 * 25 * @property allowDuplicates defines if the state observers should be notified or not 26 * if the new state produced by the reducer function is the same as the previous one. 27 */ 28 internal abstract class StateMachine<STATE, ACTION>( 29 private val allowDuplicates: Boolean, 30 ) : Subject<STATE>() { 31 32 /** 33 * The current state of the tool. 34 */ 35 protected abstract var currentState: STATE 36 37 /** 38 * The entity that observes the changes in the state. 39 */ 40 private var observable: Observer<STATE>? = null 41 42 /** 43 * Registers an observer for state updates. When registering the observer also receives 44 * immediately the current state (Hot observable). 45 */ registernull46 final override fun register(observer: Observer<STATE>) { 47 observable = observer 48 observer.render(currentState) 49 } 50 51 /** 52 * Removes an observer from the list. 53 */ unregisternull54 final override fun unregister() { 55 observable = null 56 } 57 58 /** 59 * Notifies the new state to all of the [Observer]. 60 */ updateStatenull61 final override fun updateState(newState: STATE) { 62 if (!allowDuplicates && currentState != newState) { 63 currentState = newState 64 observable?.render(newState) 65 } 66 } 67 68 /** 69 * Public function to accept actions from outside. 70 */ handleActionnull71 fun handleAction(action: ACTION) { 72 updateState(reducer(currentState, action)) 73 } 74 75 /** 76 * This function processes the current state and an action to produce a new one. 77 */ reducernull78 protected abstract fun reducer(state: STATE, action: ACTION): STATE 79 } 80