/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import {fork} from 'child_process';
import {BuiltPackage} from '../config/index';

/**
 * Builds the release output without polluting the process stdout. Build scripts commonly
 * print messages to stderr or stdout. This is fine in most cases, but sometimes other tooling
 * reserves stdout for data transfer (e.g. when `ng release build --json` is invoked). To not
 * pollute the stdout in such cases, we launch a child process for building the release packages
 * and redirect all stdout output to the stderr channel (which can be read in the terminal).
 */
export async function buildReleaseOutput(): Promise<BuiltPackage[]|null> {
  return new Promise(resolve => {
    const buildProcess = fork(require.resolve('./build-worker'), [], {
      // The stdio option is set to redirect any "stdout" output directly to the "stderr" file
      // descriptor. An additional "ipc" file descriptor is created to support communication with
      // the build process. https://nodejs.org/api/child_process.html#child_process_options_stdio.
      stdio: ['inherit', 2, 2, 'ipc'],
    });
    let builtPackages: BuiltPackage[]|null = null;

    // The child process will pass the `buildPackages()` output through the
    // IPC channel. We keep track of it so that we can use it as resolve value.
    buildProcess.on('message', buildResponse => builtPackages = buildResponse);

    // On child process exit, resolve the promise with the received output.
    buildProcess.on('exit', () => resolve(builtPackages));
  });
}