class MigrateLookup

class MigrateLookup implements MigrateLookupInterface {
    
    /**
     * The migration plugin manager.
     *
     * @var \Drupal\migrate\Plugin\MigrationPluginManagerInterface
     */
    protected $migrationPluginManager;
    
    /**
     * Constructs a MigrateLookup object.
     *
     * @param \Drupal\migrate\Plugin\MigrationPluginManagerInterface $migration_plugin_manager
     *   The migration plugin manager.
     */
    public function __construct(MigrationPluginManagerInterface $migration_plugin_manager) {
        $this->migrationPluginManager = $migration_plugin_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public function lookup($migration_id, array $source_id_values) {
        $results = [];
        $migrations = $this->migrationPluginManager
            ->createInstances($migration_id);
        if (!$migrations) {
            if (is_array($migration_id)) {
                if (count($migration_id) != 1) {
                    throw new PluginException("Plugin IDs '" . implode("', '", $migration_id) . "' were not found.");
                }
                $migration_id = reset($migration_id);
            }
            throw new PluginNotFoundException($migration_id);
        }
        foreach ($migrations as $migration) {
            if ($result = $this->doLookup($migration, $source_id_values)) {
                $results = array_merge($results, $result);
            }
        }
        return $results;
    }
    
    /**
     * Performs a lookup.
     *
     * @param \Drupal\migrate\Plugin\MigrationInterface $migration
     *   The migration upon which to perform the lookup.
     * @param array $source_id_values
     *   The source ID values to look up.
     *
     * @return array
     *   An array of arrays of destination identifier values.
     *
     * @throws \Drupal\migrate\MigrateException
     *   Thrown when $source_id_values contains unknown keys, or the wrong number
     *   of keys.
     */
    protected function doLookup(MigrationInterface $migration, array $source_id_values) {
        $destination_keys = array_keys($migration->getDestinationPlugin()
            ->getIds());
        $indexed_ids = $migration->getIdMap()
            ->lookupDestinationIds($source_id_values);
        $keyed_ids = [];
        foreach ($indexed_ids as $id) {
            $keyed_ids[] = array_combine($destination_keys, $id);
        }
        return $keyed_ids;
    }

}