QueryHandler.ts

/**
 * Copyright 2020 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

export interface QueryHandler {
  (element: Element | Document, selector: string):
    | Element
    | Element[]
    | NodeListOf<Element>;
}

const _customQueryHandlers = new Map<string, QueryHandler>();

export function registerCustomQueryHandler(
  name: string,
  handler: Function
): void {
  if (_customQueryHandlers.get(name))
    throw new Error(`A custom query handler named "${name}" already exists`);

  const isValidName = /^[a-zA-Z]+$/.test(name);
  if (!isValidName)
    throw new Error(`Custom query handler names may only contain [a-zA-Z]`);

  _customQueryHandlers.set(name, handler as QueryHandler);
}

/**
 * @param {string} name
 */
export function unregisterCustomQueryHandler(name: string): void {
  _customQueryHandlers.delete(name);
}

export function customQueryHandlers(): Map<string, QueryHandler> {
  return _customQueryHandlers;
}

export function clearQueryHandlers(): void {
  _customQueryHandlers.clear();
}

export function getQueryHandlerAndSelector(
  selector: string,
  defaultQueryHandler: QueryHandler
): { updatedSelector: string; queryHandler: QueryHandler } {
  const hasCustomQueryHandler = /^[a-zA-Z]+\//.test(selector);
  if (!hasCustomQueryHandler)
    return { updatedSelector: selector, queryHandler: defaultQueryHandler };

  const index = selector.indexOf('/');
  const name = selector.slice(0, index);
  const updatedSelector = selector.slice(index + 1);
  const queryHandler = customQueryHandlers().get(name);
  if (!queryHandler)
    throw new Error(
      `Query set to use "${name}", but no query handler of that name was found`
    );

  return {
    updatedSelector,
    queryHandler,
  };
}