jump-back-oostock.php

<?php

class iWC_Orderby_Stock_Status {
public function __construct() {
    if (in_array('woocommerce/woocommerce.php', apply_filters('active_plugins', get_option('active_plugins')))) {
        add_filter('posts_clauses', array($this, 'order_by_stock_status'), 2000);
    }
}
public function order_by_stock_status($posts_clauses) {
    global $wpdb;   
    // if you got another taxonomy u wanna use change "if" section like is_tax("product_brand")
    if (is_woocommerce() && (is_shop() || is_tax("product_brand") || is_product_taxonomy() || is_product_category() || is_product_tag())) {
        $posts_clauses['join'] .= " INNER JOIN $wpdb->postmeta istockstatus ON ($wpdb->posts.ID = istockstatus.post_id) ";
        $posts_clauses['orderby'] = " istockstatus.meta_value ASC, " . $posts_clauses['orderby'];
        $posts_clauses['where'] = " AND istockstatus.meta_key = '_stock_status' AND istockstatus.meta_value <> '' " . $posts_clauses['where'];
    }
    return $posts_clauses;
    }
}
new iWC_Orderby_Stock_Status;