WTF-Adventure/client/utils/transition.js

export default class Transition {
  constructor() {
    this.startValue = 0;
    this.endValue = 0;
    this.duration = 0;
    this.inProgress = false;
  }

  start(
    currentTime,
    updateFunction,
    stopFunction,
    startValue,
    endValue,
    duration,
  ) {
    this.startTime = currentTime;
    this.updateFunction = updateFunction;
    this.stopFunction = stopFunction;
    this.startValue = startValue;
    this.endValue = endValue;
    this.duration = duration;

    this.inProgress = true;
    this.count = 0;
  }

  step(currentTime) {
    if (!this.inProgress) {
      return;
    }

    if (this.count > 0) {
      this.count -= 1;
    } else {
      let elapsed = currentTime - this.startTime;

      if (elapsed > this.duration) {
        elapsed = this.duration;
      }

      const diff = this.endValue - this.startValue;

      const interval = Math.round(
        this.startValue + (diff / this.duration) * elapsed,
      );

      if (elapsed === this.duration || interval === this.endValue) {
        this.stop();
        if (this.stopFunction) {
          this.stopFunction();
        }
      } else if (this.updateFunction) {
        this.updateFunction(interval);
      }
    }
  }

  restart(currentTime, startValue, endValue) {
    this.start(
      currentTime,
      this.updateFunction,
      this.stopFunction,
      startValue,
      endValue,
      this.duration,
    );
    this.step(currentTime);
  }

  stop() {
    this.inProgress = false;
  }
}