var container = document.querySelector('.page-container')
// 获取根元素高度, 页面可视高度
var viewHeight = document.documentElement.clientHeight
// 获取滚动的页数
var pageNum = document.querySelectorAll('.page-item').length
// 初始化当前位置, 距离原始顶部距离
var currentPosition = 0
// 设置页面高度
container.style.height = viewHeight + 'px'

// 向下滚动页面
function goDown () {
  if (currentPosition > - viewHeight * (pageNum - 1)) {
    currentPosition = currentPosition - viewHeight
    container.style.top = currentPosition + 'px'
  }
}

// 向上滚动页面
function goUp () {
  if (currentPosition < 0) {
    currentPosition = currentPosition + viewHeight
    container.style.top = currentPosition + 'px'
  }
}

function throttle (fn, delay) {
  let baseTime = 0
  return function () {
    const currentTime = Date.now()
    if (baseTime + delay < currentTime) {
      fn.apply(this, arguments)
      baseTime = currentTime
    }
  }
}

var handlerWheel = throttle(scrollMove, 1000)
// https://developer.mozilla.org/en-US/docs/Web/API/Element/mousewheel_event#The_detail_property
// firefox的页面滚动事件其他浏览器不一样
if (navigator.userAgent.toLowerCase().indexOf('firefox') === -1) {
  document.addEventListener('mousewheel', handlerWheel)
} else {
  document.addEventListener('DOMMouseScroll', handlerWheel)
}
function scrollMove (e) {
  if (e.deltaY > 0) {
    goDown()
  } else {
    goUp()
  }
}

var touchStartY = 0
document.addEventListener('touchstart', event => {
  touchStartY = event.touches[0].pageY
})
var handleTouchEnd = throttle(touchEnd, 500)
document.addEventListener('touchend', handleTouchEnd)
function touchEnd (e) {
  var touchEndY = e.changedTouches[0].pageY
  if (touchEndY - touchStartY < 0) { // 向上滑动, 页面向下滚动
    goDown()
  } else {
    goUp()
  }
}