(function (window, undefined) {
  "use strict";
  // test for REM unit support
  var cssremunit = function () {
      var div = document.createElement("div");
      div.style.cssText = "font-size: 1rem;";

      return /rem/.test(div.style.fontSize);
    },
    // filter returned links for stylesheets
    isStyleSheet = function () {
      var styles = document.getElementsByTagName("link"),
        filteredLinks = [];

      for (var i = 0; i < styles.length; i++) {
        if (
          styles[i].rel.toLowerCase() === "stylesheet" &&
          styles[i].getAttribute("data-norem") === null
        ) {
          filteredLinks.push(styles[i].href);
        }
      }

      return filteredLinks;
    },
    processLinks = function () {
      //prepare to match each link
      for (var i = 0; i < links.length; i++) {
        xhr(links[i], storeCSS);
      }
    },
    storeCSS = function (response, link) {
      preCSS.push(response.responseText);
      CSSLinks.push(link);

      if (CSSLinks.length === links.length) {
        for (var j = 0; j < CSSLinks.length; j++) {
          matchCSS(preCSS[j], CSSLinks[j]);
        }

        if ((links = importLinks.slice(0)).length > 0) {
          //after finishing all current links, set links equal to the new imports found
          CSSLinks = [];
          preCSS = [];
          importLinks = [];
          processLinks();
        } else {
          buildCSS();
        }
      }
    },
    matchCSS = function (sheetCSS, link) {
      // collect all of the rules from the xhr response texts and match them to a pattern
      var clean = removeMediaQueries(sheetCSS).replace(/\/\*[\s\S]*?\*\//g, ""), // remove MediaQueries and comments
        pattern =
          /[\w\d\s\-\/\\\[\]:,.'"*()<>+~%#^$_=|@]+\{[\w\d\s\-\/\\%#:!;,.'"*()]+\d*\.?\d+rem[\w\d\s\-\/\\%#:!;,.'"*()]*\}/g, //find selectors that use rem in one or more of their rules
        current = clean.match(pattern),
        remPattern = /\d*\.?\d+rem/g,
        remCurrent = clean.match(remPattern),
        sheetPathPattern = /(.*\/)/,
        sheetPath = sheetPathPattern.exec(link)[0], //relative path to css file specified in @import
        importPattern = /@import (?:url\()?['"]?([^'\)"]*)['"]?\)?[^;]*/gm, //matches all @import variations outlined at: https://developer.mozilla.org/en-US/docs/Web/CSS/@import
        importStatement;

      while ((importStatement = importPattern.exec(sheetCSS)) !== null) {
        if (importStatement[1].indexOf("/") === 0) {
          // check if the value of importStatement[1] is a root relative path, in which case it shouldn't be concatenated with sheetPath
          importLinks.push(importStatement[1]);
        } else {
          importLinks.push(sheetPath + importStatement[1]);
        }
      }

      if (current !== null && current.length !== 0) {
        found = found.concat(current); // save all of the blocks of rules with rem in a property
        foundProps = foundProps.concat(remCurrent); // save all of the properties with rem
      }
    },
    buildCSS = function () {
      // first build each individual rule from elements in the found array and then add it to the string of rules.
      var pattern =
        /[\w\d\s\-\/\\%#:,.'"*()]+\d*\.?\d+rem[\w\d\s\-\/\\%#:!,.'"*()]*[;}]/g; // find properties with rem values in them
      for (var i = 0; i < found.length; i++) {
        rules = rules + found[i].substr(0, found[i].indexOf("{") + 1); // save the selector portion of each rule with a rem value
        var current = found[i].match(pattern);
        for (var j = 0; j < current.length; j++) {
          // build a new set of with only the selector and properties that have rem in the value
          rules = rules + current[j];
          if (j === current.length - 1 && rules[rules.length - 1] !== "}") {
            rules = rules + "\n}";
          }
        }
      }

      parseCSS();
    },
    parseCSS = function () {
      // replace each set of parentheses with evaluated content
      for (var i = 0; i < foundProps.length; i++) {
        css[i] =
          Math.round(
            parseFloat(
              foundProps[i].substr(0, foundProps[i].length - 3) * fontSize
            )
          ) + "px";
      }

      loadCSS();
    },
    loadCSS = function () {
      // replace and load the new rules
      for (var i = 0; i < css.length; i++) {
        // only run this loop as many times as css has entries
        if (css[i]) {
          rules = rules.replace(foundProps[i], css[i]); // replace old rules with our processed rules
        }
      }
      var remcss = document.createElement("style");
      remcss.setAttribute("type", "text/css");
      remcss.id = "remReplace";
      document.getElementsByTagName("head")[0].appendChild(remcss); // create the new element
      if (remcss.styleSheet) {
        remcss.styleSheet.cssText = rules; // IE8 will not support innerHTML on read-only elements, such as STYLE
      } else {
        remcss.appendChild(document.createTextNode(rules));
      }
    },
    xhr = function (url, callback) {
      // create new XMLHttpRequest object and run it
      try {
        //try to create a request object
        //arranging the two conditions this way is for IE7/8's benefit
        //so that it works with any combination of ActiveX or Native XHR settings,
        //as long as one or the other is enabled; but if both are enabled
        //it prefers ActiveX, which means it still works with local files
        //(Native XHR in IE7/8 is blocked and throws "access is denied",
        // but ActiveX is permitted if the user allows it [default is to prompt])
        var xhr = window.ActiveXObject
          ? new ActiveXObject("Microsoft.XMLHTTP") ||
            new ActiveXObject("Msxml2.XMLHTTP")
          : new XMLHttpRequest();

        xhr.open("GET", url, true);
        xhr.onreadystatechange = function () {
          if (xhr.readyState === 4) {
            callback(xhr, url);
          } // else { callback function on AJAX error }
        };

        xhr.send(null);
      } catch (e) {
        if (window.XDomainRequest) {
          var xdr = new XDomainRequest();
          xdr.open("get", url);
          xdr.onload = function () {
            callback(xdr, url);
          };
          xdr.onerror = function () {
            return false; // xdr load fail
          };
          xdr.send();
        }
      }
    },
    // Remove queries.
    removeMediaQueries = function (css) {
      // Test for Media Query support
      if (!window.matchMedia && !window.msMatchMedia) {
        // If the browser doesn't support media queries, we find all @media declarations in the CSS and remove them.
        // Note: Since @rules can't be nested in the CSS spec, we're safe to just check for the closest following "}}" to the "@media".
        css = css.replace(/@media[\s\S]*?\}\s*\}/g, "");
      }

      return css;
    };

  if (!cssremunit()) {
    // this checks if the rem value is supported
    var rules = "", // initialize the rules variable in this scope so it can be used later
      links = isStyleSheet(), // initialize the array holding the sheets urls for use later
      importLinks = [], //initialize the array holding the import sheet urls for use later
      found = [], // initialize the array holding the found rules for use later
      foundProps = [], // initialize the array holding the found properties for use later
      preCSS = [], // initialize array that holds css before being parsed
      CSSLinks = [], //initialize array holding css links returned from xhr
      css = [], // initialize the array holding the parsed rules for use later
      fontSize = "";

    // Notice: rem is a "root em" that means that in case when html element size was changed by css
    // or style we should not change document.documentElement.fontSize to 1em - only body size should be changed
    // to 1em for calculation

    fontSize = (function () {
      var doc = document,
        docElement = doc.documentElement,
        body = doc.body || doc.createElement("body"),
        isFakeBody = !doc.body,
        div = doc.createElement("div"),
        currentSize = body.style.fontSize,
        size;

      if (isFakeBody) {
        docElement.appendChild(body);
      }

      div.style.cssText =
        "width:1em; position:absolute; visibility:hidden; padding: 0;";

      body.style.fontSize = "1em";

      body.appendChild(div);
      size = div.offsetWidth;

      if (isFakeBody) {
        docElement.removeChild(body);
      } else {
        body.removeChild(div);
        body.style.fontSize = currentSize;
      }

      return size;
    })();

    processLinks();
  } // else { do nothing, you are awesome and have REM support }
})(window);