/**
 * Copyright 2013 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 ReactComponentWithPureRender
*/

"use strict";

/**
 * If your React component's render function is "pure", e.g. it will render the
 * same result given the same props and state, provide this Mixin for a
 * considerable performance boost.
 *
 * Most React components have pure render functions.
 *
 * Example:
 *
 *   var ReactComponentWithPureRender = require('ReactComponentWithPureRender');
 *   React.createClass({
 *     mixins: [ReactComponentWithPureRender],
 *
 *     render: function() {
 *       return <div className={this.props.className}>foo</div>;
 *     }
 *   });
 *
 * Note: This only checks shallow equality for props and state. If these contain
 * complex data structures this mixin may have false-negatives for deeper
 * differences. Only mixin to components which have simple props and state, or
 * use `forceUpdate()` when you know deep data structures have changed.
 */
var ReactComponentWithPureRender = {
  shouldComponentUpdate: function(nextProps, nextState) {
    return !shallowEqual(this.props, nextProps) ||
           !shallowEqual(this.state, nextState);
  }
};

/**
 * Performs equality by iterating through keys on an object and returning
 * false when any key has values which are not strictly equal between
 * objA and objB. Returns true when the values of all keys are strictly equal.
 */
function shallowEqual(objA, objB) {
  if (objA === objB) {
    return true;
  }
  var key;
  // Test for A's keys different from B.
  for (key in objA) {
    if (objA.hasOwnProperty(key) &&
        (!objB.hasOwnProperty(key) || objA[key] !== objB[key])) {
      return false;
    }
  }
  // Test for B'a keys missing from A.
  for (key in objB) {
    if (objB.hasOwnProperty(key) && !objA.hasOwnProperty(key)) {
      return false;
    }
  }
  return true;
}

module.exports = ReactComponentWithPureRender;
