Progress.js

import speedometer from './speedometer';

export default class Progress {
  constructor(length, emitDelay = 1000) {
    this.length = parseInt(length, 10) || 0;
    this.transferred = 0;
    this.speed = 0;
    this.streamSpeed = speedometer(this.speed || 5000);
    this.initial = false;
    this.emitDelay = emitDelay;
    this.eventStart = 0;
    this.percentage = 0;
  }

  getRemainingBytes() {
    return parseInt(this.length, 10) - parseInt(this.transferred, 10);
  }

  getEta() {
    return this.length >= this.transferred
      ? this.getRemainingBytes() / this.speed * 1000000000
      : 0;
  }

  flow(chunk, onProgress) {
    const chunkLength = chunk.length;
    this.transferred += chunkLength;
    this.speed = this.streamSpeed(chunkLength);
    this.percentage = Math.round(this.transferred / this.length * 100);
    if (!this.initial) {
      this.eventStart = Date.now();
      this.initial = true;
    }
    if (
      this.length >= this.transferred ||
      Date.now() - this.eventStart > this.emitDelay
    ) {
      this.eventStart = Date.now();

      const progress = {
        total: this.length,
        transferred: this.transferred,
        speed: this.speed,
        eta: this.getEta(),
      };
      if (this.length) {
        progress.remaining = this.getRemainingBytes();
        progress.percentage = this.percentage;
      }
      onProgress(progress);
    }
  }
}