Parse paths relatives to a source.
@param  {String} source      Where the paths originate from
@param  {Array}  stylesheets List of paths
@param  {Object} options     Options, as passed to UnCSS
@return {Array}              List of paths
function parsePaths(source, stylesheets, options) {
    return stylesheets.map((sheet) => {
        let sourceProtocol;
        const isLocalFile = sheet.substr(0, 5) === 'file:';

        if (sheet.substr(0, 4) === 'http') {
            /* No need to parse, it's already a valid path */
            return sheet;
        }

        /* Check if we are fetching over http(s) */
        if (isURL(source) && !isLocalFile) {
            sourceProtocol = url.parse(source).protocol;

            if (sheet.substr(0, 2) === '//') {
                /* Use the same protocol we used for fetching this page.
                 * Default to http.
                 */
                return sourceProtocol ? sourceProtocol + sheet : 'http:' + sheet;
            }
            return url.resolve(source, sheet);
        }

        /* We are fetching local files
         * Should probably report an error if we find an absolute path and
         *   have no htmlroot specified.
         */
        /* Fix the case when there is a query string or hash */
        sheet = sheet.split('?')[0].split('#')[0];

        /* Path already parsed by jsdom or user supplied local file */
        if (isLocalFile) {
            sheet = url.parse(sheet).path.replace('%20', ' ');
            /* If on windows, remove first '/' */
            sheet = isWindows() ? sheet.substring(1) : sheet;

            if (options.htmlroot) {
                return path.join(options.htmlroot, sheet);
            }
            sheet = path.relative(path.join(path.dirname(source)), sheet);
        }

        if (sheet[0] === '/' && options.htmlroot) {
            return path.join(options.htmlroot, sheet);
        } else if (isHTML(source)) {
            return path.join(options.csspath, sheet);
        }
        return path.join(path.dirname(source), options.csspath, sheet);
    });
}