/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * 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 type ValidationContext from '../ValidationContext';
import { GraphQLError } from '../../error';
import type { ASTVisitor } from '../../language/visitor';

export function duplicateOperationNameMessage(operationName: string): string {
  return `There can be only one operation named "${operationName}".`;
}

/**
 * Unique operation names
 *
 * A GraphQL document is only valid if all defined operations have unique names.
 */
export function UniqueOperationNames(context: ValidationContext): ASTVisitor {
  const knownOperationNames = Object.create(null);
  return {
    OperationDefinition(node) {
      const operationName = node.name;
      if (operationName) {
        if (knownOperationNames[operationName.value]) {
          context.reportError(
            new GraphQLError(
              duplicateOperationNameMessage(operationName.value),
              [knownOperationNames[operationName.value], operationName],
            ),
          );
        } else {
          knownOperationNames[operationName.value] = operationName;
        }
      }
      return false;
    },
    FragmentDefinition: () => false,
  };
}