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]));
    }

}