elm-review/lib/sync-get.js

Run elm-review from Node.js

/**
 * @import {PortResponse, WorkerData} from './types/sync-get';
 */

const path = require('node:path');
const {
  Worker,
  MessageChannel,
  receiveMessageOnPort
} = require('node:worker_threads');
const Result = require('./result');

/**
 * Start a worker thread and return a `syncGetWorker`
 *
 * Capable of making sync requests until shut down.
 *
 * @returns {{get: (url : string) => string, shutDown: () => void}}
 */
function startWorker() {
  const {port1: localPort, port2: workerPort} = new MessageChannel();
  const sharedLock = new SharedArrayBuffer(4);
  const sharedLockArray = new Int32Array(sharedLock);
  const workerPath = path.resolve(__dirname, 'sync-get-worker.js');
  const worker = new Worker(workerPath, {
    workerData: /** @satisfies {WorkerData} */ ({
      sharedLock,
      requestPort: workerPort
    }),
    transferList: [workerPort]
  });

  /**
   * @param {string} url
   * @returns {string}
   */
  function get(url) {
    worker.postMessage(url);
    Atomics.wait(sharedLockArray, 0, 0); // Blocks until notified at index 0.
    /** @type {{ message: PortResponse } | undefined} */
    const response = receiveMessageOnPort(localPort);
    if (!response?.message) {
      return '';
    }

    return Result.orThrow(response.message);
  }

  /**
   * Shut down the worker thread.
   *
   * @returns {void}
   */
  function shutDown() {
    localPort.close();
    void worker.terminate();
  }

  return {get, shutDown};
}

module.exports = {
  startWorker
};