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;
        }
    }

}