/**
 * 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 SyntheticWheelEvent
 * @typechecks static-only
 */

"use strict";

var SyntheticMouseEvent = require('SyntheticMouseEvent');

/**
 * @interface WheelEvent
 * @see http://www.w3.org/TR/DOM-Level-3-Events/
 */
var WheelEventInterface = {
  deltaX: function(event) {
    return (
      'deltaX' in event ? event.deltaX :
      // Fallback to `wheelDeltaX` for Webkit and normalize (right is positive).
      'wheelDeltaX' in event ? -event.wheelDeltaX : 0
    );
  },
  deltaY: function(event) {
    return (
      'deltaY' in event ? event.deltaY :
      // Fallback to `wheelDeltaY` for Webkit and normalize (down is positive).
      'wheelDeltaY' in event ? -event.wheelDeltaY :
      // Fallback to `wheelDelta` for IE<9 and normalize (down is positive).
      'wheelDelta' in event ? -event.wheelDelta : 0
    );
  },
  deltaZ: null,

  // Browsers without "deltaMode" is reporting in raw wheel delta where one
  // notch on the scroll is always +/- 120, roughly equivalent to pixels.
  // A good approximation of DOM_DELTA_LINE (1) is 5% of viewport size or
  // ~40 pixels, for DOM_DELTA_SCREEN (2) it is 87.5% of viewport size.
  deltaMode: null
};

/**
 * @param {object} dispatchConfig Configuration used to dispatch this event.
 * @param {string} dispatchMarker Marker identifying the event target.
 * @param {object} nativeEvent Native browser event.
 * @extends {SyntheticMouseEvent}
 */
function SyntheticWheelEvent(dispatchConfig, dispatchMarker, nativeEvent) {
  SyntheticMouseEvent.call(this, dispatchConfig, dispatchMarker, nativeEvent);
}

SyntheticMouseEvent.augmentClass(SyntheticWheelEvent, WheelEventInterface);

module.exports = SyntheticWheelEvent;
