<template>
  <div class="sticky" :style="getPosition">
    <div class="sticky-warp">
      <slot></slot>
    </div>
  </div>
</template>

<style scoped lang="less" rel="stylesheet/less">
  .sticky {
    width: 100%;
    .sticky-warp {
      width: 100%;
      background: inherit;
      will-change: change;
      height: inherit;
      top: inherit;
    }
  }
</style>

<script type="text/babel">
  export default {
    data () {
      return {}
    },
    computed: {
      getPosition(){
        var position = this.cssSupport('position', 'sticky') ? 'sticky' : 'relative';
        return 'position:' + position;
      }
    },
    props: {},
    beforeMount () {
    },
    mounted(){
      this.init();
    },
    deactivated(){
      if(this.cssSupport('position', 'sticky')) {
        return;
      }
      /*复位*/
      var elWarp = this.$el.querySelector('.sticky-warp');
      elWarp.position = 'absolute';
    },
    methods: {
      init(){
        if (this.cssSupport('position', 'sticky')) {
          return;
        }
        var el = this.$el, target = this.$el.parentNode,
            elWarp = this.$el.querySelector('.sticky-warp'),
            top = this.getNumberValue(document.defaultView.getComputedStyle(el).top);
        this.addScrollListen(target, (event)=> {
          if (el.getBoundingClientRect().top <= top) {
            elWarp.style.position = 'fixed';
          }
          if (el.getBoundingClientRect().top >= 0 && elWarp.style.position != 'absolute') {
            elWarp.style.position = 'absolute';
          }
        })
      },
      cssSupport: function (attr, value) {
        var element = document.createElement('div');
        if (attr in element.style) {
          element.style[attr] = value;
          return element.style[attr] === value;
        } else {
          return false;
        }
      },
      getNumberValue(pxValue){
        var value = String(pxValue).match(/^\-?\+?[0-9]+/g);
        return value ? Number(value) : undefined;
      },
      addScrollListen(target, cb){
        target.addEventListener('y-scroll', (event)=> {
          cb && cb(event);
        });
      }
    },
  }

 
</script>