/**
 * 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 ReactEventTopLevelCallback
 * @typechecks static-only
 */

"use strict";

var ExecutionEnvironment = require('ExecutionEnvironment');
var ReactEventEmitter = require('ReactEventEmitter');
var ReactID = require('ReactID');
var ReactInstanceHandles = require('ReactInstanceHandles');

var getEventTarget = require('getEventTarget');

/**
 * @type {boolean}
 * @private
 */
var _topLevelListenersEnabled = true;

/**
 * Top-level callback creator used to implement event handling using delegation.
 * This is used via dependency injection in `ReactEventEmitter.ensureListening`.
 */
var ReactEventTopLevelCallback = {

  /**
   * Sets whether or not any created callbacks should be enabled.
   *
   * @param {boolean} enabled True if callbacks should be enabled.
   */
  setEnabled: function(enabled) {
    _topLevelListenersEnabled = !!enabled;
  },

  /**
   * @return {boolean} True if callbacks are enabled.
   */
  isEnabled: function() {
    return _topLevelListenersEnabled;
  },

  /**
   * Creates a callback for the supplied `topLevelType` that could be added as
   * a listener to the document. The callback computes a `topLevelTarget` which
   * should be the root node of a mounted React component where the listener
   * is attached.
   *
   * @param {string} topLevelType Record from `EventConstants`.
   * @return {function} Callback for handling top-level events.
   */
  createTopLevelCallback: function(topLevelType) {
    return function(nativeEvent) {
      if (!_topLevelListenersEnabled) {
        return;
      }
      // TODO: Remove when synthetic events are ready, this is for IE<9.
      if (nativeEvent.srcElement &&
          nativeEvent.srcElement !== nativeEvent.target) {
        nativeEvent.target = nativeEvent.srcElement;
      }
      var topLevelTarget = ReactInstanceHandles.getFirstReactDOM(
        getEventTarget(nativeEvent)
      ) || ExecutionEnvironment.global;
      var topLevelTargetID = ReactID.getID(topLevelTarget) || '';
      ReactEventEmitter.handleTopLevel(
        topLevelType,
        topLevelTarget,
        topLevelTargetID,
        nativeEvent
      );
    };
  }

};

module.exports = ReactEventTopLevelCallback;