private function handle_form()
 {
     $config = SitemapConfig::load();
     if ($this->form->get_value('enable_sitemap_xml')) {
         $config->enable_sitemap_xml_generation();
         $config->set_sitemap_xml_life_time((int) $this->form->get_value('file_life_time'));
     } else {
         $config->disable_sitemap_xml_generation();
     }
     SitemapConfig::save($config);
 }
 private static function update_last_generation_date()
 {
     $sitemap_config = SitemapConfig::load();
     $sitemap_config->set_last_generation_date(new Date());
     SitemapConfig::save($sitemap_config);
 }