1// Copyright (C) 2024 The Android Open Source Project 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14 15type Reducer = () => unknown; 16type Callback = () => void; 17 18/** 19 * A little helper that monitors a list of immutable objects and calls a 20 * callback only when at least one them changes. 21 */ 22export class Monitor { 23 private cached: unknown[]; 24 25 constructor(private reducers: Reducer[]) { 26 this.cached = reducers.map(() => undefined); 27 } 28 29 /** 30 * Invokes all reducers and compares values against with the previous values. 31 * 32 * If any of the values have changed, |callback| is called (if present) and 33 * returns true, otherwise no callback is called and returns false. 34 * 35 * @param callback Optional callback to call when diffs are detected. 36 * @returns True if diffs were detected, false otherwise. 37 */ 38 ifStateChanged(callback?: Callback): boolean { 39 const oldState = this.cached; 40 const newState = this.reducers.map((f) => f()); 41 this.cached = newState; 42 if (newState.some((x, i) => x !== oldState[i])) { 43 callback?.(); 44 return true; 45 } 46 47 return false; 48 } 49} 50