import cs from 'classnames';

class FixedTab extends React.Component{
 constructor(props){
   super(props);
   
   this.state = {
    navTop: false
   }

   this.$tab = null;
   this.offsetTop = 0;
 }

 componentDidMount(){
  this.$tab = this.refs.tab;
  if(this.$tab){
   this.offsetTop = this.$tab.offsetTop;
   window.addEventListener('scroll',this.handleScroll);
  }
 }

 handleScroll(){
  let sTop = document.documentElement.scrollTop || window.pageYOffset || document.body.scrollTop;

  if(sTop >= this.offsetTop){
    this.setState({
     navTop: true
    })
  }

  if(sTop < this.offsetTop){
    this.setState({
     navTop:false
    })
  }
 }

 render(){
  return(
    <div ref="tab" className={cs({'fixed':this.state.navTop})}></div>
  )
 } 
}

handleScroll(){
  let sTop = document.documentElement.scrollTop || window.pageYOffset || document.body.scrollTop;

  if(!this.state.navTop && sTop >= this.offsetTop){
    this.setState({
     navTop: true
    })
  }

  if(sTop < this.offsetTop){
    this.setState({
     navTop:false
    })
  }
 }