/**
 * @file
 * Used to load CSS via JS so css doesn't block the browser.
 */

/* @codingStandardsIgnoreFile */
/* eslint-disable */

/*! loadCSS. [c]2017 Filament Group, Inc. MIT License */
/* This file is meant as a standalone workflow for
- testing support for link[rel=preload]
- enabling async CSS loading in browsers that do not support rel=preload
- applying rel preload css once loaded, whether supported or not.
*/
(function( w ){
  "use strict";
  // rel=preload support test
  if( !w.loadCSS ){
    w.loadCSS = function(){};
  }
  // define on the loadCSS obj
  var rp = loadCSS.relpreload = {};
  // rel=preload feature support test
  // runs once and returns a function for compat purposes
  rp.support = (function(){
    var ret;
    try {
      ret = w.document.createElement( "link" ).relList.supports( "preload" );
    } catch (e) {
      ret = false;
    }
    return function(){
      return ret;
    };
  })();

  // if preload isn't supported, get an asynchronous load by using a non-matching media attribute
  // then change that media back to its intended value on load
  rp.bindMediaToggle = function( link ){
    // remember existing media attr for ultimate state, or default to 'all'
    var finalMedia = link.media || "all";

    function enableStylesheet(){
      link.media = finalMedia;
    }

    // bind load handlers to enable media
    if( link.addEventListener ){
      link.addEventListener( "load", enableStylesheet );
    } else if( link.attachEvent ){
      link.attachEvent( "onload", enableStylesheet );
    }

    // Set rel and non-applicable media type to start an async request
    // note: timeout allows this to happen async to let rendering continue in IE
    setTimeout(function(){
      link.rel = "stylesheet";
      link.media = "only x";
    });
    // also enable media after 3 seconds,
    // which will catch very old browsers (android 2.x, old firefox) that don't support onload on link
    setTimeout( enableStylesheet, 3000 );
  };

  // loop through link elements in DOM
  rp.poly = function(){
    // double check this to prevent external calls from running
    if( rp.support() ){
      return;
    }
    var links = w.document.getElementsByTagName( "link" );
    for( var i = 0; i < links.length; i++ ){
      var link = links[ i ];
      // qualify links to those with rel=preload and as=style attrs
      if( link.rel === "preload" && link.getAttribute( "as" ) === "style" && !link.getAttribute( "data-loadcss" ) ){
        // prevent rerunning on link
        link.setAttribute( "data-loadcss", true );
        // bind listeners to toggle media back
        rp.bindMediaToggle( link );
      }
    }
  };

  // if unsupported, run the polyfill
  if( !rp.support() ){
    // run once at least
    rp.poly();

    // rerun poly on an interval until onload
    var run = w.setInterval( rp.poly, 500 );
    if( w.addEventListener ){
      w.addEventListener( "load", function(){
        rp.poly();
        w.clearInterval( run );
      } );
    } else if( w.attachEvent ){
      w.attachEvent( "onload", function(){
        rp.poly();
        w.clearInterval( run );
      } );
    }
  }


  // commonjs
  if( typeof exports !== "undefined" ){
    exports.loadCSS = loadCSS;
  }
  else {
    w.loadCSS = loadCSS;
  }
}( typeof global !== "undefined" ? global : this ) );
