class BlockPluginId

class BlockPluginId extends ProcessPluginBase implements ContainerFactoryPluginInterface {
  
  /**
   * The migrate lookup service.
   *
   * @var \Drupal\migrate\MigrateLookupInterface
   */
  protected $migrateLookup;
  
  /**
   * The block_content entity storage handler.
   *
   * @var \Drupal\Core\Entity\EntityStorageInterface
   */
  protected $blockContentStorage;
  
  /**
   * Constructs a BlockPluginId object.
   *
   * @param array $configuration
   *   The plugin configuration.
   * @param string $plugin_id
   *   The plugin ID.
   * @param array $plugin_definition
   *   The plugin definition.
   * @param \Drupal\Core\Entity\EntityStorageInterface $storage
   *   The block content storage object.
   * @param \Drupal\migrate\MigrateLookupInterface $migrate_lookup
   *   The migrate lookup service.
   */
  public function __construct(array $configuration, $plugin_id, array $plugin_definition, EntityStorageInterface $storage, MigrateLookupInterface $migrate_lookup) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->blockContentStorage = $storage;
    $this->migrateLookup = $migrate_lookup;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
    $entity_type_manager = $container->get('entity_type.manager');
    return new static($configuration, $plugin_id, $plugin_definition, $entity_type_manager->getDefinition('block_content') ? $entity_type_manager->getStorage('block_content') : NULL, $container->get('migrate.lookup'));
  }
  
  /**
   * {@inheritdoc}
   *
   * Set the block plugin id.
   */
  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
    if (is_array($value)) {
      [
        $module,
        $delta,
      ] = $value;
      switch ($module) {
        case 'aggregator':
          [
            $type,
          ] = explode('-', $delta);
          if ($type == 'feed') {
            return 'aggregator_feed_block';
          }
          break;

        case 'menu':
          return "system_menu_block:{$delta}";
        case 'block':
          if ($this->blockContentStorage) {
            $lookup_result = $this->migrateLookup
              ->lookup([
              'd6_custom_block',
              'd7_custom_block',
            ], [
              $delta,
            ]);
            if ($lookup_result) {
              $block_id = $lookup_result[0]['id'];
              return 'block_content:' . $this->blockContentStorage
                ->load($block_id)
                ->uuid();
            }
          }
          break;

        default:
          break;

      }
    }
    else {
      return $value;
    }
  }

}