Currently when you browse through the products pages on our wp-e-commerce WordPress site, all of the out of stock products show across all the pages.

What we would like to be able to to do, is to move all of the out of stock products to the end of the pages, so that in order to view the out of stock products, you would have to scroll through all the pages, which would be showing the products that are in stock, in order to improve the user experience.

We would like to be able to either come up with a filter to go in functions.php, or change the below code to achieve this:

 `class OrderWpscProducts {

  // flag for when a shop products post query is being created
  private $isProductQuery = false;

  public function __construct() {
  // hooks for altering order of product pages
  add_filter('parse_query', array($this, 'filterProductQueryMark'), 20);
  add_filter('posts_join', array($this, 'filterProductQueryJoins'), 20);
  add_filter('posts_orderby', array($this, 'filterProductQueryOrderBy'), 20);
  }

  /**
  * detect a posts query that should return a list of shop products,
  * and mark it for later filters
  * @param WP_Query $query
  * @return WP_Query
  */
  public function filterProductQueryMark($query) {
  $this->isProductQuery = false;

  if (!is_admin() && (wpsc_is_in_category() || !empty($query->query_vars['wpsc_wine_style']))) {
    $this->isProductQuery = true;
  }
  }

  /**
  * if the posts query is for a list of shop products,
  * then add some tables to the join so that we can sort by category name
  * @param string $joins
  * @return string
  */
  public function filterProductQueryJoins($joins) {
  global $wpdb;

  if ($this->isProductQuery) {
  $joins .= "
  INNER JOIN $wpdb->term_relationships wpsc_cat_rel ON wp_posts.ID = wpsc_cat_rel.object_id
  INNER JOIN $wpdb->term_taxonomy wpsc_cat_tax ON wpsc_cat_tax.term_taxonomy_id =                        wpsc_cat_rel.term_taxonomy_id
  and wpsc_cat_tax.taxonomy = 'wpsc_product_category'
  INNER JOIN $wpdb->terms wpsc_cat ON wpsc_cat.term_id = wpsc_cat_tax.term_id
  "; }

  return $joins;
  }

  /**
  * if the posts query is for a list of shop products, then sort by category name and product title
  * @param string $orderby
  * @return string
  */
  public function filterProductQueryOrderBy($orderby) {
  if ($this->isProductQuery) {
    $orderby = 'wpsc_cat.name ASC, wp_posts.post_title ASC';
  }

  return $orderby;
  }
  }

  // create instance, will be kept alive by hooks
  new OrderWpscProducts(); `

Had a go at trying to create a filter (still new to php, but had a go with the following).

If anyone has any suggestions on how the above code could be changed to move the out of stock products to the end of the pages, or how the below filter could be changed to achieve that, it would be really appreciated:

add_filter('posts_clauses', 'order_by_stock_status');
function order_by_stock_status($posts_clauses) {
global $wpdb;
// only change query on wp-e-commerce loops
if (!is_admin() && (is_productQuery() || is_wpsc_product_category() || is_product_tag() ||          is_wpsc_cat.taxonomy_id())) {
$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;
}