code: public static function getOperation(DocumentNode $document, $operationName = null)
      {
          if ($document->definitions) {
              foreach ($document->definitions as $def) {
                  if (! ($def instanceof OperationDefinitionNode)) {
                      continue;
                  }
  
                  if (! $operationName || (isset($def->name->value) && $def->name->value === $operationName)) {
                      return $def->operation;
                  }
              }
          }
  
          return false;
      }
docs: Returns operation type ("query", "mutation" or "subscription") given a document and operation name
  
  @param string $operationName
  
  @return bool
  
  @api