export const TouchEmulator = (() => {
  /**
   * 模拟移动端 touch 事件
   */
  var eventTarget

  // polyfills
  if (!document.createTouch) {
    document.createTouch = function (
      view,
      target,
      identifier,
      pageX,
      pageY,
      screenX,
      screenY
    ) {
      // auto set
      return new Touch(
        target,
        identifier,
        {
          pageX: pageX,
          pageY: pageY,
          screenX: screenX,
          screenY: screenY,
          clientX: pageX - window.pageXOffset,
          clientY: pageY - window.pageYOffset,
        },
        0,
        0
      )
    }
  }

  if (!document.createTouchList) {
    document.createTouchList = function () {
      var touchList = TouchList()
      for (var i = 0; i < arguments.length; i++) {
        touchList[i] = arguments[i]
      }
      touchList.length = arguments.length
      return touchList
    }
  }

  /**
   * create an touch point
   * @constructor
   * @param target
   * @param identifier
   * @param pos
   * @param deltaX
   * @param deltaY
   * @returns {Object} touchPoint
   */

  var Touch = function Touch(target, identifier, pos, deltaX, deltaY) {
    deltaX = deltaX || 0
    deltaY = deltaY || 0

    this.identifier = identifier
    this.target = target
    this.clientX = pos.clientX + deltaX
    this.clientY = pos.clientY + deltaY
    this.screenX = pos.screenX + deltaX
    this.screenY = pos.screenY + deltaY
    this.pageX = pos.pageX + deltaX
    this.pageY = pos.pageY + deltaY
  }

  /**
   * create empty touchlist with the methods
   * @constructor
   * @returns touchList
   */
  function TouchList() {
    var touchList = []

    touchList['item'] = function (index) {
      return this[index] || null
    }

    // specified by Mozilla
    touchList['identifiedTouch'] = function (id) {
      return this[id + 1] || null
    }

    return touchList
  }

  /**
   * Simple trick to fake touch event support
   * this is enough for most libraries like Modernizr and Hammer
   */
  function fakeTouchSupport() {
    var objs = [window, document.documentElement]
    var props = ['ontouchstart', 'ontouchmove', 'ontouchcancel', 'ontouchend']

    for (var o = 0; o < objs.length; o++) {
      for (var p = 0; p < props.length; p++) {
        if (objs[o] && objs[o][props[p]] === undefined) {
          objs[o][props[p]] = null
        }
      }
    }
  }

  /**
   * only trigger touches when the left mousebutton has been pressed
   * @param touchType
   * @returns {Function}
   */
  function onMouse(touchType) {
    return function (ev) {
      // prevent mouse events

      if (ev.which !== 1) {
        return
      }

      // The EventTarget on which the touch point started when it was first placed on the surface,
      // even if the touch point has since moved outside the interactive area of that element.
      // also, when the target doesnt exist anymore, we update it
      if (
        ev.type === 'mousedown' ||
        !eventTarget ||
        (eventTarget && !eventTarget.dispatchEvent)
      ) {
        eventTarget = ev.target
      }

      triggerTouch(touchType, ev)

      // reset
      if (ev.type === 'mouseup') {
        eventTarget = null
      }
    }
  }

  /**
   * trigger a touch event
   * @param eventName
   * @param mouseEv
   */
  function triggerTouch(eventName, mouseEv) {
    var touchEvent = document.createEvent('Event')
    touchEvent.initEvent(eventName, true, true)

    touchEvent.altKey = mouseEv.altKey
    touchEvent.ctrlKey = mouseEv.ctrlKey
    touchEvent.metaKey = mouseEv.metaKey
    touchEvent.shiftKey = mouseEv.shiftKey

    touchEvent.touches = getActiveTouches(mouseEv)
    touchEvent.targetTouches = getActiveTouches(mouseEv)
    touchEvent.changedTouches = createTouchList(mouseEv)

    eventTarget.dispatchEvent(touchEvent)
  }

  /**
   * create a touchList based on the mouse event
   * @param mouseEv
   * @returns {TouchList}
   */
  function createTouchList(mouseEv) {
    var touchList = TouchList()
    touchList.push(new Touch(eventTarget, 1, mouseEv, 0, 0))
    return touchList
  }

  /**
   * receive all active touches
   * @param mouseEv
   * @returns {TouchList}
   */
  function getActiveTouches(mouseEv) {
    // empty list
    if (mouseEv.type === 'mouseup') {
      return TouchList()
    }
    return createTouchList(mouseEv)
  }

  /**
   * TouchEmulator initializer
   */
  function TouchEmulator(target) {
    fakeTouchSupport()

    target.addEventListener('mousedown', onMouse('touchstart'), true)
    target.addEventListener('mousemove', onMouse('touchmove'), true)
    target.addEventListener('mouseup', onMouse('touchend'), true)
  }

  // start distance when entering the multitouch mode
  TouchEmulator['multiTouchOffset'] = 75

  return TouchEmulator
})()