(function() {
  const vueSticky = {};
  let listenAction;
  vueSticky.install = Vue => {
    Vue.directive('sticky', {
      inserted(el, binding) {
        const params = binding.value || {},
          stickyTop = params.stickyTop || 0,
          zIndex = params.zIndex || 1000,
          elStyle = el.style;

        elStyle.position = '-webkit-sticky';
        elStyle.position = 'sticky';
        // if the browser support css sticky（Currently Safari, Firefox and Chrome Canary）
        // if (~elStyle.position.indexOf('sticky')) {
        //     elStyle.top = `${stickyTop}px`;
        //     elStyle.zIndex = zIndex;
        //     return
        // }
        const elHeight = el.getBoundingClientRect().height;
        const elWidth = el.getBoundingClientRect().width;
        elStyle.cssText = `top: ${stickyTop}px; z-index: ${zIndex}`;

        const parentElm = el.parentNode || document.documentElement;
        const placeholder = document.createElement('div');
        placeholder.style.display = 'none';
        placeholder.style.width = `${elWidth}px`;
        placeholder.style.height = `${elHeight}px`;
        parentElm.insertBefore(placeholder, el)

        let active = false;

        const getScroll = (target, top) => {
          const prop = top ? 'pageYOffset' : 'pageXOffset';
          const method = top ? 'scrollTop' : 'scrollLeft';
          let ret = target[prop];
          if (typeof ret !== 'number') {
            ret = window.document.documentElement[method];
          }
          return ret;
        };

        const sticky = () => {
          if (active) {
            return
          }
          if (!elStyle.height) {
            elStyle.height = `${el.offsetHeight}px`
          }

          elStyle.position = 'fixed';
          elStyle.width = `${elWidth}px`;
          placeholder.style.display = 'inline-block';
          active = true
        };

        const reset = () => {
          if (!active) {
            return
          }

          elStyle.position = '';
          placeholder.style.display = 'none';
          active = false;
        };

        const check = () => {
          const scrollTop = getScroll(window, true);
          const offsetTop = el.getBoundingClientRect().top;
          if (offsetTop < stickyTop) {
            sticky();
          } else {
            if (scrollTop < elHeight + stickyTop) {
              reset()
            }
          }
        };
        listenAction = () => {
          check()
        };

        window.addEventListener('scroll', listenAction)
      },

      unbind() {
        window.removeEventListener('scroll', listenAction)
      }
    })
  };
  if (typeof exports == 'object') {
    module.exports = vueSticky
  } else if (typeof define == 'function' && define.amd) {
    define([], () => vueSticky)
  } else if (window.Vue) {
    window.vueSticky = vueSticky;
    Vue.use(vueSticky)
  }
}());

