Subtheme of Radix subtheme post-processing

StarterKit.php

<?php
namespace Drupal\hd_radix;

use Drupal\Core\Theme\StarterKitInterface;
use Symfony\Component\Filesystem\Filesystem;

final class StarterKit implements StarterKitInterface {

  const HD_RADIX_RELATIVE_PATH = '../hd_radix';

  /**
   * {@inheritdoc}
   */
  public static function postProcess(string $working_dir, string $machine_name, string $theme_name): void {
    self::removeBuiltAssets($working_dir,$machine_name);
    self::symlinkNodeModules($working_dir, $machine_name);
    self::importSCSSAssets($working_dir, $machine_name);
  }

  /**
   * Delete copied node_modules directory and replace it with symlinkfrom hd_radix
   *
   * @param string $working_dir
   * @param string $machine_name
   *
   * @return void
   */
  private static function symlinkNodeModules(string $working_dir, string $machine_name) {
    $fs = new Filesystem();
    $fs->remove("{$working_dir}/node_modules");
    $fs->symlink( self::HD_RADIX_RELATIVE_PATH ."/node_modules", "{$working_dir}/node_modules");
  }

  /**
   * Delete built assets copied from hd_radix
   *
   * @param string $working_dir
   * @param string $machine_name
   *
   * @return void
   */
  private static function removeBuiltAssets(string $working_dir, string $machine_name) {
    $fs = new Filesystem();
    $fs->remove("{$working_dir}/build");
  }

  /**
   * Add import statement to the top of base SCSS files
   *
   * @param string $working_dir
   * @param string $machine_name
   *
   * @return void
   */
  private static function importSCSSAssets(string $working_dir, string $machine_name) {
    $fs = new Filesystem();
    $base_scss_path = "src/scss/base";
    $base_files = [
      'elements',
      'functions',
      'helpers',
      'mixins',
      'typography',
      'utilities'
    ];
    foreach ($base_files as $base_file) {
      $content = "\n@import \"../../../" . self::HD_RADIX_RELATIVE_PATH . "/{$base_scss_path}/{$base_file}\";";
      $fs->appendToFile("{$working_dir}/{$base_scss_path}/_{$base_file}.scss",$content);
    }
  }
}