public static function update_internal_fees()
 {
     $id = Core::validate(self::getVar('id'));
     $fieldName = Core::validate(self::getVar('fieldName'));
     $value = Core::validate(self::getVar('value'));
     $goodInput = false;
     switch ($fieldName) {
         case 'Fee':
             if ($value != null && Core::isDouble($value) && $value >= 0) {
                 $goodInput = true;
             }
             break;
         default:
             break;
     }
     if ($goodInput == true) {
         $rate = new Rate();
         $rate->setId($id);
         $rate->update(array($fieldName => $value));
         Core::printSuccessJson('');
     } else {
         Core::printErrorJson('Invalid input: ' . $value);
     }
 }