/**
 * 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.
 *
 *  strict
 */

import { GraphQLError } from '../../error';


export function duplicateVariableMessage(variableName) {
  return 'There can be only one variable named "' + variableName + '".';
}

/**
 * Unique variable names
 *
 * A GraphQL operation is only valid if all its variables are uniquely named.
 */
export function UniqueVariableNames(context) {
  var knownVariableNames = Object.create(null);
  return {
    OperationDefinition: function OperationDefinition() {
      knownVariableNames = Object.create(null);
    },
    VariableDefinition: function VariableDefinition(node) {
      var variableName = node.variable.name.value;
      if (knownVariableNames[variableName]) {
        context.reportError(new GraphQLError(duplicateVariableMessage(variableName), [knownVariableNames[variableName], node.variable.name]));
      } else {
        knownVariableNames[variableName] = node.variable.name;
      }
    }
  };
}