/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow strict
 */

import { Kind } from '../language/kinds';
import {
  type DocumentNode,
  type OperationDefinitionNode,
} from '../language/ast';

/**
 * Returns an operation AST given a document AST and optionally an operation
 * name. If a name is not provided, an operation is only returned if only one is
 * provided in the document.
 */
export function getOperationAST(
  documentAST: DocumentNode,
  operationName: ?string,
): ?OperationDefinitionNode {
  let operation = null;
  for (let i = 0; i < documentAST.definitions.length; i++) {
    const definition = documentAST.definitions[i];
    if (definition.kind === Kind.OPERATION_DEFINITION) {
      if (!operationName) {
        // If no operation name was provided, only return an Operation if there
        // is one defined in the document. Upon encountering the second, return
        // null.
        if (operation) {
          return null;
        }
        operation = definition;
      } else if (definition.name && definition.name.value === operationName) {
        return definition;
      }
    }
  }
  return operation;
}