job.js

import EventEmitter from 'eventemitter3';

export default class Job extends EventEmitter {
  constructor(pool) {
    super();
    this.pool   = pool;
    this.thread = null;

    this.runArgs = [];
    this.sendArgs = [];

    pool.emit('newJob', this);
  }

  run(...args) {
    if (args.length === 0) {
      throw new Error('Cannot call .run() without arguments.');
    }

    this.runArgs = args;
    return this;
  }

  send(...args) {
    if (this.runArgs.length === 0) {
      throw new Error('Cannot .send() before .run().');
    }

    this.sendArgs = args;

    this.emit('readyToRun');
    return this;
  }

  executeOn(thread) {
    const onProgress = (...args) => this.emit('progress', ...args);
    const onMessage = (...args) => {
      this.emit('done', ...args);
      thread.removeListener('progress', onProgress);
    };
    const onError = (...args) => {
      this.emit('error', ...args);
      thread.removeListener('progress', onProgress);
    };
    
    thread
      .on('progress', onProgress)
      .once('message', onMessage)
      .once('error', onError)
      .run(...this.runArgs)
      .send(...this.sendArgs);

    this.thread = thread;
    this.emit('threadChanged');
    return this;
  }

  promise() {
    // Always return a promise
    return new Promise((resolve) => {
      // If the thread isn't set, listen for the threadChanged event
      if (!this.thread) {
        this.once('threadChanged', () => {
          resolve(this.thread.promise());
        });
      } else {
        resolve(this.thread.promise());
      }
    });
  }

  destroy () {
    this.removeAllListeners();
    delete this.runArgs;
    delete this.sendArgs;
  }
}