class MenuLinkParent

class MenuLinkParent extends ProcessPluginBase implements ContainerFactoryPluginInterface {
  
  /**
   * The menu link plugin manager.
   *
   * @var \Drupal\Core\Menu\MenuLinkManagerInterface
   */
  protected $menuLinkManager;
  
  /**
   * The currently running migration.
   *
   * @var \Drupal\migrate\Plugin\MigrationInterface
   */
  protected $migration;
  
  /**
   * The migrate lookup service.
   *
   * @var \Drupal\migrate\MigrateLookupInterface
   */
  protected $migrateLookup;
  
  /**
   * The menu link entity storage handler.
   *
   * @var \Drupal\Core\Entity\EntityStorageInterface
   */
  protected $menuLinkStorage;
  
  /**
   * Constructs a MenuLinkParent object.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\migrate\MigrateLookupInterface $migrate_lookup
   *   The migrate lookup service.
   * @param \Drupal\Core\Menu\MenuLinkManagerInterface $menu_link_manager
   *   The menu link manager.
   * @param \Drupal\Core\Entity\EntityStorageInterface $menu_link_storage
   *   The menu link storage object.
   * @param \Drupal\migrate\Plugin\MigrationInterface $migration
   *   The currently running migration.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrateLookupInterface $migrate_lookup, MenuLinkManagerInterface $menu_link_manager, EntityStorageInterface $menu_link_storage, MigrationInterface $migration) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->migration = $migration;
    $this->migrateLookup = $migrate_lookup;
    $this->menuLinkManager = $menu_link_manager;
    $this->menuLinkStorage = $menu_link_storage;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('migrate.lookup'), $container->get('plugin.manager.menu.link'), $container->get('entity_type.manager')
      ->getStorage('menu_link_content'), $migration);
  }
  
  /**
   * {@inheritdoc}
   *
   * Find the parent link GUID.
   */
  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
    $parent_id = array_shift($value);
    // Handle root elements of a menu.
    if (!$parent_id) {
      return '';
    }
    $lookup_result = $this->migrateLookup
      ->lookup($this->migration
      ->id(), [
      $parent_id,
    ]);
    if ($lookup_result) {
      $already_migrated_id = $lookup_result[0]['id'];
    }
    if (!empty($already_migrated_id) && $link = $this->menuLinkStorage
      ->load($already_migrated_id)) {
      return $link->getPluginId();
    }
    // Parent could not be determined by ID, so we try to determine by the
    // combination of the menu name and parent link path.
    if (isset($value[1])) {
      [$menu_name, $parent_link_path] = $value;
      // If the parent link path is external, URL will be useless because the
      // link will definitely not correspond to a Drupal route.
      if (UrlHelper::isExternal($parent_link_path)) {
        $links = $this->menuLinkStorage
          ->loadByProperties([
          'menu_name' => $menu_name,
          'link.uri' => $parent_link_path,
        ]);
      }
      else {
        $url = Url::fromUserInput('/' . ltrim($parent_link_path, '/'));
        if ($url->isRouted()) {
          $links = $this->menuLinkManager
            ->loadLinksByRoute($url->getRouteName(), $url->getRouteParameters(), $menu_name);
        }
      }
      if (!empty($links)) {
        return reset($links)->getPluginId();
      }
    }
    // Parent could not be determined.
    throw new MigrateSkipRowException(sprintf("No parent link found for plid '%d' in menu '%s'.", $parent_id, $value[0]));
  }

}