/************* Add sorting by attributes **************/

/**
 *  Defines the criteria for sorting with options defined in the method below
 */
add_filter('woocommerce_get_catalog_ordering_args', 'custom_woocommerce_get_catalog_ordering_args');

function custom_woocommerce_get_catalog_ordering_args( $args ) {
    global $wp_query;
        // Changed the $_SESSION to $_GET
    if (isset($_GET['orderby'])) {
        switch ($_GET['orderby']) :
            case 'velikost1' :
                $args['order'] = 'ASC';
                $args['meta_key'] = 'velikost';
                $args['orderby'] = 'meta_value_num';
            break;
            case 'velikost2' :
                $args['order'] = 'DESC';
                $args['meta_key'] = 'velikost';
                $args['orderby'] = 'meta_value_num';
            break;
        endswitch;
    }
    return $args;
}

/**
 *  Adds the sorting options to dropdown list .. The logic/criteria is in the method above
 */
add_filter('woocommerce_catalog_orderby', 'custom_woocommerce_catalog_orderby');

function custom_woocommerce_catalog_orderby( $sortby ) {
    $sortby['velikost_1'] = 'Seřadit podle velikosti 1';
    $sortby['velikost_2'] = 'Seřadit podle velikosti 2';
    return $sortby;
}



/**
 *  Save custom attributes as post's meta data as well so that we can use in sorting and searching
 */
add_action( 'save_post', 'save_woocommerce_attr_to_meta' );
function save_woocommerce_attr_to_meta( $post_id ) {
        // Get the attribute_names .. For each element get the index and the name of the attribute
        // Then use the index to get the corresponding submitted value from the attribute_values array.
    foreach( $_REQUEST['attribute_names'] as $index => $value ) {
        update_post_meta( $post_id, $value, $_REQUEST['attribute_values'][$index] );
    }
}
/************ End of Sorting ***************************/