var React = require('react');

module.exports = {

  isInViewport: function() {

    var el = React.findDOMNode(this);

    if(!el) return false;

    var rect = el.getBoundingClientRect();

    return (
      rect.top >= 0 &&
      rect.left >= 0 &&
      rect.bottom <= (global.window.innerHeight || global.document.documentElement.clientHeight) && /*or $(window).height() */
      rect.right <= (global.window.innerWidth || global.document.documentElement.clientWidth) /*or $(window).width() */
    );

  },

  componentDidMount: function() {

    function _onInViewport(){
      if( this.isInViewport() ) {
        this.onInViewport();
      }
    }

    var el = React.findDOMNode(this);

    if(typeof this.onInViewport === 'function') {
      window.document.addEventListener('scroll', debounce(_onInViewport.bind(this), 250), true);
    }

    _onInViewport.call(this);

  }

};

function debounce(func, wait, immediate) {
  var timeout;
	return function() {
		var context = this, args = arguments;
		var later = function() {
			timeout = null;
			if (!immediate) func.apply(context, args);
		};
		var callNow = immediate && !timeout;
		clearTimeout(timeout);
		timeout = setTimeout(later, wait);
		if (callNow) func.apply(context, args);
	};
}