content: import React from 'react';
  import ColumnHeader from './column_header';
  import PropTypes from 'prop-types';
  import { debounce } from 'lodash';
  
  const easingOutQuint = (x, t, b, c, d) => c*((t=t/d-1)*t*t*t*t + 1) + b;
  
  const scrollTop = (node) => {
    const startTime = Date.now();
    const offset    = node.scrollTop;
    const targetY   = -offset;
    const duration  = 1000;
    let interrupt   = false;
  
    const step = () => {
      const elapsed    = Date.now() - startTime;
      const percentage = elapsed / duration;
  
      if (percentage > 1 || interrupt) {
        return;
      }
  
      node.scrollTop = easingOutQuint(0, elapsed, offset, targetY, duration);
      requestAnimationFrame(step);
    };
  
    step();
  
    return () => {
      interrupt = true;
    };
  };
  
  class Column extends React.PureComponent {
  
    static propTypes = {
      heading: PropTypes.string,
      icon: PropTypes.string,
      children: PropTypes.node,
      active: PropTypes.bool,
      hideHeadingOnMobile: PropTypes.bool,
    };
  
    handleHeaderClick = () => {
      const scrollable = this.node.querySelector('.scrollable');
      if (!scrollable) {
        return;
      }
      this._interruptScrollAnimation = scrollTop(scrollable);
    }
  
    handleScroll = debounce(() => {
      if (typeof this._interruptScrollAnimation !== 'undefined') {
        this._interruptScrollAnimation();
      }
    }, 200)
  
    setRef = (c) => {
      this.node = c;
    }
  
    render () {
      const { heading, icon, children, active, hideHeadingOnMobile } = this.props;
  
      let columnHeaderId = null;
      let header = '';
  
      if (heading) {
        columnHeaderId = heading.replace(/ /g, '-');
        header = <ColumnHeader icon={icon} active={active} type={heading} onClick={this.handleHeaderClick} hideOnMobile={hideHeadingOnMobile} columnHeaderId={columnHeaderId}/>;
      }
      return (
        <div
          ref={this.setRef}
          role='region'
          aria-labelledby={columnHeaderId}
          className='column'
          onScroll={this.handleScroll}>
          {header}
          {children}
        </div>
      );
    }
  
  }
  
  export default Column;
  