const { Worker, isMainThread, parentPort, workerData } = require('worker_threads');

// Here's the worker, of which we'll run several concurrent instances.
// These workers will receive work on the `workerData` and send the corresponding
// results back to the main thread. We'll use a setTimeout to simulate an expensive task.
if (!isMainThread) {
  const worker = async (id, job) => {
    console.log(`worker ${id} started job ${job}`);
    await new Promise(resolve => setTimeout(resolve, 1000));
    console.log(`worker ${id} finished job ${job}`);
    parentPort.postMessage(job * 2);
  };

  worker(workerData.id, workerData.job);
}

// Main thread code
if (isMainThread) {
  const numJobs = 5;
  const numWorkers = 3;
  let completedJobs = 0;

  // This function creates a new worker
  const createWorker = (id, job) => {
    return new Promise((resolve) => {
      const worker = new Worker(__filename, {
        workerData: { id, job }
      });
      worker.on('message', (result) => {
        console.log(`Job ${job} returned ${result}`);
        completedJobs++;
        if (completedJobs === numJobs) {
          console.log('All jobs completed');
        }
        resolve(result);
      });
    });
  };

  // This starts up our worker pool
  const runJobs = async () => {
    const workers = [];
    for (let i = 1; i <= numJobs; i++) {
      const workerId = (i - 1) % numWorkers + 1;
      workers.push(createWorker(workerId, i));
      
      // If we've queued up enough jobs to fill the worker pool,
      // wait for one to complete before queueing more
      if (workers.length === numWorkers) {
        await Promise.race(workers);
        workers.length = 0;
      }
    }
    
    // Wait for any remaining jobs
    await Promise.all(workers);
  };

  console.time('Jobs completed in');
  runJobs().then(() => console.timeEnd('Jobs completed in'));
}