/**
 * Copyright 2013-2014 Facebook, Inc.
 *
 * 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.
 *
 * @providesModule CSSCore
 * @typechecks
 */

var invariant = require('invariant');

/**
 * The CSSCore module specifies the API (and implements most of the methods)
 * that should be used when dealing with the display of elements (via their
 * CSS classes and visibility on screen. It is an API focused on mutating the
 * display and not reading it as no logical state should be encoded in the
 * display of elements.
 */

var CSSCore = {

  /**
   * Adds the class passed in to the element if it doesn't already have it.
   *
   * @param {DOMElement} element the element to set the class on
   * @param {string} className the CSS className
   * @return {DOMElement} the element passed in
   */
  addClass: function(element, className) {
    invariant(
      !/\s/.test(className),
      'CSSCore.addClass takes only a single class name. "%s" contains ' +
      'multiple classes.', className
    );

    if (className) {
      if (element.classList) {
        element.classList.add(className);
      } else if (!CSSCore.hasClass(element, className)) {
        element.className = element.className + ' ' + className;
      }
    }
    return element;
  },

  /**
   * Removes the class passed in from the element
   *
   * @param {DOMElement} element the element to set the class on
   * @param {string} className the CSS className
   * @return {DOMElement} the element passed in
   */
  removeClass: function(element, className) {
    invariant(
      !/\s/.test(className),
      'CSSCore.removeClass takes only a single class name. "%s" contains ' +
      'multiple classes.', className
    );

    if (className) {
      if (element.classList) {
        element.classList.remove(className);
      } else if (CSSCore.hasClass(element, className)) {
        element.className = element.className
          .replace(new RegExp('(^|\\s)' + className + '(?:\\s|$)', 'g'), '$1')
          .replace(/\s+/g, ' ') // multiple spaces to one
          .replace(/^\s*|\s*$/g, ''); // trim the ends
      }
    }
    return element;
  },

  /**
   * Helper to add or remove a class from an element based on a condition.
   *
   * @param {DOMElement} element the element to set the class on
   * @param {string} className the CSS className
   * @param {*} bool condition to whether to add or remove the class
   * @return {DOMElement} the element passed in
   */
  conditionClass: function(element, className, bool) {
    return (bool ? CSSCore.addClass : CSSCore.removeClass)(element, className);
  },

  /**
   * Tests whether the element has the class specified.
   *
   * @param {DOMNode|DOMWindow} element the element to set the class on
   * @param {string} className the CSS className
   * @returns {boolean} true if the element has the class, false if not
   */
  hasClass: function(element, className) {
    invariant(
      !/\s/.test(className),
      'CSS.hasClass takes only a single class name.'
    );
    if (element.classList) {
      return !!className && element.classList.contains(className);
    }
    return (' ' + element.className + ' ').indexOf(' ' + className + ' ') > -1;
  }

};

module.exports = CSSCore;
