help understanding this code [closed]

Question

I have this code in a site that I am trying to understand. I don't get exactly what it does. I get some of it but not all

  $nav_posts = $wpdb->get_results( "SELECT id FROM $wpdb->posts WHERE post_type =  'nav_menu_item' and post_status = 'publish' ORDER BY menu_order ASC" );
 $exclude = $base_pages = array();

foreach($nav_posts as $nav) {

    $_menu_item_object = get_post_meta($nav->id,'_menu_item_object',true);

    $post_status = get_post_status( get_post_meta($nav->id,'_menu_item_object_id',true) );

    if($_menu_item_object=='page' && $post_status=='publish') {

        $exclude[] = $_menu_item_object_id = get_post_meta($nav->id,'_menu_item_object_id',true);

        $base_pages[] = get_post($_menu_item_object_id); 

    }

}

$second_pages = get_pages(array('exclude'=>$exclude));

$pages = array_merge($base_pages,$second_pages);