/**
 * 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 { GraphQLError } from '../error/GraphQLError';
import { type ASTNode } from '../language/ast';
import invariant from '../jsutils/invariant';

const NAME_RX = /^[_a-zA-Z][_a-zA-Z0-9]*$/;

/**
 * Upholds the spec rules about naming.
 */
export function assertValidName(name: string): string {
  const error = isValidNameError(name);
  if (error) {
    throw error;
  }
  return name;
}

/**
 * Returns an Error if a name is invalid.
 */
export function isValidNameError(
  name: string,
  node?: ASTNode | void,
): GraphQLError | void {
  invariant(typeof name === 'string', 'Expected string');
  if (name.length > 1 && name[0] === '_' && name[1] === '_') {
    return new GraphQLError(
      `Name "${name}" must not begin with "__", which is reserved by ` +
        'GraphQL introspection.',
      node,
    );
  }
  if (!NAME_RX.test(name)) {
    return new GraphQLError(
      `Names must match /^[_a-zA-Z][_a-zA-Z0-9]*$/ but "${name}" does not.`,
      node,
    );
  }
}