import React,{ PureComponent } from 'react';


export const getScrollTop = () => {
  let scroll_top = 0;
  if (document.documentElement && document.documentElement.scrollTop) {
    scroll_top = document.documentElement.scrollTop;
  }
  else if (document.body) {
    scroll_top = document.body.scrollTop;
  }
  return scroll_top;
};

const checkInPage = el => {
  const pageHeight = document.documentElement.clientHeight;
  const contentTop = el.getBoundingClientRect().top;
  const contentHeight = el.offsetHeight;
  return (contentTop < pageHeight && contentTop >= 0) || (contentTop < 0 && (contentTop + contentHeight > 0));
};

const lazyLoading = ({ minHeight = 0 }) => (ChildComponent) => {
  return class extends PureComponent{

    static defaultProps={
      lazyLoading:true
    };

    state = {
      visible:false
    };

    checkInPage = () => {
      let isVisible = checkInPage(this.el);
      let { visible } = this.state;
      if ( visible === true ){
        window.removeEventListener('scroll',this.checkInPage);
        return;
      }
      this.setState({ visible:isVisible });
    };

    componentDidMount(){
      if ( this.props.lazyLoading === false ){
        return;
      }
      setTimeout(()=>{ 
        this.checkInPage();
        window.addEventListener('scroll',this.checkInPage);
      },200)
    }

    componentWillUnmount(){
      if ( this.props.lazyLoading === false ){
        return;
      }
      window.removeEventListener('scroll',this.checkInPage);
    }

    render(){

      if ( this.props.lazyLoading === false ){
        return <ChildComponent {...this.props} />
      }

      return <div ref={el=>this.el=el} style={{ minHeight }} >
        { this.state.visible && <ChildComponent {...this.props} /> }
      </div>
    }
  }
};

export default lazyLoading;