/**
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule TapEventPlugin
 */

'use strict';

var EventConstants = require('./EventConstants');
var EventPluginUtils = require('./EventPluginUtils');
var EventPropagators = require('./EventPropagators');
var SyntheticUIEvent = require('./SyntheticUIEvent');
var TouchEventUtils = require('fbjs/lib/TouchEventUtils');
var ViewportMetrics = require('./ViewportMetrics');

var keyOf = require('fbjs/lib/keyOf');
var topLevelTypes = EventConstants.topLevelTypes;

var isStartish = EventPluginUtils.isStartish;
var isEndish = EventPluginUtils.isEndish;

/**
 * Number of pixels that are tolerated in between a `touchStart` and `touchEnd`
 * in order to still be considered a 'tap' event.
 */
var tapMoveThreshold = 10;
var startCoords = { x: null, y: null };

var Axis = {
  x: { page: 'pageX', client: 'clientX', envScroll: 'currentPageScrollLeft' },
  y: { page: 'pageY', client: 'clientY', envScroll: 'currentPageScrollTop' }
};

function getAxisCoordOfEvent(axis, nativeEvent) {
  var singleTouch = TouchEventUtils.extractSingleTouch(nativeEvent);
  if (singleTouch) {
    return singleTouch[axis.page];
  }
  return axis.page in nativeEvent ? nativeEvent[axis.page] : nativeEvent[axis.client] + ViewportMetrics[axis.envScroll];
}

function getDistance(coords, nativeEvent) {
  var pageX = getAxisCoordOfEvent(Axis.x, nativeEvent);
  var pageY = getAxisCoordOfEvent(Axis.y, nativeEvent);
  return Math.pow(Math.pow(pageX - coords.x, 2) + Math.pow(pageY - coords.y, 2), 0.5);
}

var touchEvents = [topLevelTypes.topTouchStart, topLevelTypes.topTouchCancel, topLevelTypes.topTouchEnd, topLevelTypes.topTouchMove];

var dependencies = [topLevelTypes.topMouseDown, topLevelTypes.topMouseMove, topLevelTypes.topMouseUp].concat(touchEvents);

var eventTypes = {
  touchTap: {
    phasedRegistrationNames: {
      bubbled: keyOf({ onTouchTap: null }),
      captured: keyOf({ onTouchTapCapture: null })
    },
    dependencies: dependencies
  }
};

var usedTouch = false;
var usedTouchTime = 0;
var TOUCH_DELAY = 1000;

var TapEventPlugin = {

  tapMoveThreshold: tapMoveThreshold,

  eventTypes: eventTypes,

  extractEvents: function (topLevelType, targetInst, nativeEvent, nativeEventTarget) {
    if (!isStartish(topLevelType) && !isEndish(topLevelType)) {
      return null;
    }
    // on ios, there is a delay after touch event and synthetic
    // mouse events, so that user can perform double tap
    // solution: ignore mouse events following touchevent within small timeframe
    if (touchEvents.indexOf(topLevelType) !== -1) {
      usedTouch = true;
      usedTouchTime = Date.now();
    } else {
      if (usedTouch && Date.now() - usedTouchTime < TOUCH_DELAY) {
        return null;
      }
    }
    var event = null;
    var distance = getDistance(startCoords, nativeEvent);
    if (isEndish(topLevelType) && distance < tapMoveThreshold) {
      event = SyntheticUIEvent.getPooled(eventTypes.touchTap, targetInst, nativeEvent, nativeEventTarget);
    }
    if (isStartish(topLevelType)) {
      startCoords.x = getAxisCoordOfEvent(Axis.x, nativeEvent);
      startCoords.y = getAxisCoordOfEvent(Axis.y, nativeEvent);
    } else if (isEndish(topLevelType)) {
      startCoords.x = 0;
      startCoords.y = 0;
    }
    EventPropagators.accumulateTwoPhaseDispatches(event);
    return event;
  }

};

module.exports = TapEventPlugin;