Custom Template Styles Based on Querystring

<?php
//This filter will look an alternate template that matches displaystyle in the querystring
//http://mysite.com/products/my-product/?displaystyle=style1 will search for foxyshop-single-product-style1.php
//If it doesn't find it, the original file will be returned
//This feature is helpful for creating different styles which can be referenced by changing the querystring
//This snippet can go in functions.php
add_filter('foxyshop_template_redirect', 'my_foxyshop_template_redirect', 5, 2);
function my_foxyshop_template_redirect($final_url, $original_filename) {
    if (isset($_GET['displaystyle'])) {
        $newfilename = str_replace(".php", '-' . sanitize_title_with_dashes($_GET['displaystyle']) . '.php', $original_filename);
        if (file_exists(STYLESHEETPATH . '/' . $newfilename)) {
            return STYLESHEETPATH . '/' . $newfilename;
        }
    }
    return $final_url;
}
?>