@react-native-ohos/flash-list/src/utils/AverageWindow.ts

FlashList is a more performant FlatList replacement

/**
 * MIT License
 *
 * Copyright (C) 2024 Huawei Device Co., Ltd.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/**
 * Helper class to calculate running average of the most recent n values
 */
export class AverageWindow {
  private currentAverage: number;
  private currentCount: number;
  private inputValues: (number | undefined)[];
  private nextIndex = 0;
  constructor(size: number, startValue?: number) {
    this.inputValues = new Array<number>(Math.max(1, size));
    this.currentAverage = startValue ?? 0;
    this.currentCount = startValue === undefined ? 0 : 1;
    this.nextIndex = this.currentCount;
    this.inputValues[0] = startValue;
  }

  /**
   * Can be used to get the current average value
   */
  public get currentValue(): number {
    return this.currentAverage;
  }

  /**
   *
   * @param value Add new value to the average window and updated current average
   */
  public addValue(value: number): void {
    const target = this.getNextIndex();
    const oldValue = this.inputValues[target];
    const newCount =
      oldValue === undefined ? this.currentCount + 1 : this.currentCount;

    this.inputValues[target] = value;

    this.currentAverage =
      this.currentAverage * (this.currentCount / newCount) +
      (value - (oldValue ?? 0)) / newCount;

    this.currentCount = newCount;
  }

  private getNextIndex(): number {
    // starts from 0 once we reach end of the array
    const newTarget = this.nextIndex;
    this.nextIndex = (this.nextIndex + 1) % this.inputValues.length;
    return newTarget;
  }
}