Preselect product variant

/**
 * Detect product permalinks
 * URL Format: http://shop.com/product_slug/variation_sku
 */
function pm_detect_product_permalinks($request) {
    global $wp, $wpdb;

    // Parse the URI
    preg_match('/^(?:([a-z]{2})\/)?([^\/]+)(?:\/([^\/]+))?\/?$/i', $wp->request, $parts);

    if(!empty($parts[2])) {
            $new_request = array();

            // Get product by slug
            $product = $wpdb->get_row($wpdb->prepare("SELECT * FROM {$wpdb->posts} WHERE post_name = %s AND post_type = %s AND post_status = %s",
                sanitize_title($parts[2]),
                'product',
                'publish'
            ));

            // 1. Rewrite request array if product was found
            if(!empty($product->post_name)) {
                $new_request['name'] = $product->post_name;
                $new_request['post_type'] = 'product';
                $new_request['product'] = $product->post_name;
                $new_request['do_not_redirect'] = 1;
            }

            // 2. Get variation by SKU
            if(!empty($parts[3])) {
                $variation_id = $wpdb->get_var($wpdb->prepare("SELECT post_id FROM {$wpdb->postmeta} WHERE meta_key = %s AND meta_value = %s",
                    '_sku',
                    sanitize_title($parts[3])
                ));

                if(is_numeric($variation_id)) {
                    $product_variation = wc_get_product((int) $variation_id);
                    $variation_variations = $product_variation->get_variation_attributes();

                    // Preselect attributes
                    if(!empty($variation_variations)) {
                        foreach($variation_variations as $attr_name => $attr_value) {
                            // $attr_name = str_replace('attribute_', '', $attr);
                            $_REQUEST[$attr_name] = $attr_value;
                        }
                    }
                } else {
                    return $request;
                }
            }

            $request = $new_request;
    }

    return $request;
}
add_filter('request', 'pm_detect_product_permalinks', 99);

/**
 * Filter product permalinks
 */
function bis_filter_woo_permalinks($url, $element) {
    if(!empty($element->post_type) && ($element->post_type == 'product')) {
        $url = trim(get_option('home'), '/') . "/{$element->post_name}";
    }

    return $url;
}
add_filter('post_type_link', 'bis_filter_woo_permalinks', 999, 2);