Nodejs - dublicate background data URI in CSS - identify and group

gistfile1.js

/** 
* Match all ocurences of data uri backgrounds in css and group them if they are dupe 
* If background property contains both data-uri and other background properties, they are sparated 
*/
process: function(content) {
    function getMatches(string, regex, index) {
        index = index || 1; // default to the first capturing group
        var matches = [];
        var match;
        do {
            match = regex.exec(string);
            if (match) {
                console.log('Match found!');
                matches.push({
                    cssPath: match[1]
                    , url: match[3]
                    , extraParams: match[4]
                });
            }
        } while (match);
        return matches;
    }

    function getStyle(rulesArr) {
        return _.map(rulesArr, function(rule) {
            return rule.cssPath + '{' + rule.style + ';}\n';
        }).join('');
    }
    /*
    https://regex101.com/r/cQ9gV5/1 - this is the place were I worked to obtain this insane regex:
    It basically matches all the places where data-uris exists in CSS for backgrounds, and extracts data
    needed for processing like it follows:
    [0] => CSS rule path
    [1] => anything that exists after background and : like background[-image]:
    [2] => the full image url
    [3] => any data after the url like: url(data:....) [-10px 20px no-repeat];
    */
    var cssRegex = /\}((?:[^\{]?\n?)+)\{[^\}]+background(\S+)?\s?:\s?(url\(data:\S{2,10}\/\S{2,10};base64,[^=]+==\))(.*);/g;
    var ruleOnlyRegex = /background(\S*)\s?:\s?(url\(data:\S{2,10}\/\S{2,10};base64,[^=]*==\))(.*)/g;

    var matches = getMatches(content, cssRegex);

    var cssRulesGroups = _.values(_.groupBy(matches, function(match) {
        // return the full url
        return match.url;
    }));

    // all the rules that should be added
    var rules = [];
    var totalGrouped = 0;
    _.each(cssRulesGroups, function(sameUrlGroup) {
        if (sameUrlGroup.length > 1) {
            totalGrouped += sameUrlGroup.length;
        }
        _.each(sameUrlGroup, function(rule){
            if (rule.extraParams) {
                rules.push({
                    cssPath: rule.cssPath
                    , style: 'background:' + rule.extraParams
                });
            }
        });

        var aggregatedPaths = _.map(sameUrlGroup, function(rule) {
            return rule.cssPath;
        }).join(',');

        rules.push({
            cssPath: aggregatedPaths
            , style: 'background-image:' + sameUrlGroup[0].url
        });
    });
    console.log('Grouped ' + totalGrouped + ' data-uri CSS rules !');
    var contentWithoutData = content.replace(ruleOnlyRegex, '');
    return getStyle(rules) + contentWithoutData;
}