/**
 * Copyright 2015 CANAL+ Group
 *
 * 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.
 */

let hasClassList: boolean | undefined;

/**
 * Add className to an HTMLElement. Do nothing if the className was already
 * added.
 * @param {HTMLElement} elt
 * @param {string} className
 */
export default function addClassName(elt: HTMLElement, className: string): void {
  if (hasClassList === undefined) {
    hasClassList = elt.classList !== undefined && typeof elt.classList.add === "function";
  }

  if (hasClassList) {
    elt.classList.add(className);
  } else {
    const classNamesWithSpaces = " " + elt.className + " ";
    if (classNamesWithSpaces.indexOf(" " + className + " ") < 0) {
      elt.className += " " + className;
    }
  }
}