export default function mobileAdapt () {
  var dpr, rem, scale
  var docEl = document.documentElement
  var fontEl = document.createElement('style')
  var metaEl = document.querySelector('meta[name="viewport"]')

  dpr = window.devicePixelRatio || 2
  rem = docEl.clientWidth * dpr / 10
  scale = 1 / dpr

  // 设置viewport，进行缩放，达到高清效果
  metaEl.setAttribute('content', 'width=' + dpr * docEl.clientWidth + ',initial-scale=' + scale + ',maximum-scale=' + scale + ', minimum-scale=' + scale + ',user-scalable=no')

  // 设置data-dpr属性，留作的css hack之用
  docEl.setAttribute('data-dpr', dpr)

  // 动态写入样式
  docEl.firstElementChild.appendChild(fontEl)
  fontEl.innerHTML = 'html{font-size:' + rem + 'px!important;}'

  // 给js调用的，某一dpr下rem和px之间的转换函数
  window.rem2px = function (v) {
    v = parseFloat(v)
    return v * rem
  }
  window.px2rem = function (v) {
    v = parseFloat(v)
    return v / rem
  }

  // window.dpr = dpr
  // window.rem = rem
}