/**
  * @throws SystemMessageIDMissingException
  */
 public static function edit()
 {
     if ($_GET['id']) {
         $system_message = new SystemMessage($_GET['id']);
         if ($_GET['nextpage'] == 1) {
             $page_1_passed = true;
             if (!$_POST['content']) {
                 $page_1_passed = false;
                 $error = "You must enter a text";
             }
         } else {
             $page_1_passed = false;
             $error = "";
         }
         if ($page_1_passed == false) {
             $template = new HTMLTemplate("base/admin/system_message/edit.html");
             $paramquery = $_GET;
             $paramquery['nextpage'] = "1";
             $params = http_build_query($paramquery, '', '&');
             $template->set_var("params", $params);
             if ($error) {
                 $template->set_var("error", $error);
             } else {
                 $template->set_var("error", "");
             }
             $content = str_replace("\\", "", $system_message->get_content());
             if ($_POST['content']) {
                 $template->set_var("content", $_POST['content']);
             } else {
                 $template->set_var("content", $content);
             }
             $template->output();
         } else {
             $paramquery = $_GET;
             unset($paramquery['nextpage']);
             unset($paramquery['action']);
             $params = http_build_query($paramquery);
             if ($system_message->set_content($_POST['content'])) {
                 Common_IO::step_proceed($params, "Add System Message", "Operation Successful", null);
             } else {
                 Common_IO::step_proceed($params, "Add System Message", "Operation Failed", null);
             }
         }
     } else {
         throw new SystemMessageIDMissingException();
     }
 }