Routing issue Notice: Undefined offset?

Question

PHP

Here is an excerpt from router.class.php .
And it throws errors

Notice: Undefined offset: 2 in classes/router.php on line 5
 Notice: Undefined offset: 3 in classes/router.php on line 9
 Notice: Undefined offset: 1 in classes/router.php on line 12
 Notice: Undefined offset: 3 in classes/router.php on line 14
 Notice: Undefined offset: 4 in classes/router.php on line 15
 Notice: Undefined offset: 5 in classes/router.php on line 16

public static function executeAction() {
    
    $module = isset(self::$params[0]) ? self::$params[0]: 'index';
    $action = isset(self::$params[1]) ? self::$params[1]: 'default';
    $params = self::$params[2];
    $_GET['app'] = $action;
    $_GET['add'] = $params;
    $_GET['param'] = $params;
    $_GET['param_2'] = self::$params[3];
    $_GET['page_name'] = $module;
    $_GET['prm_0'] = isset(self::$params[0]) ? self::$params[0]: 'index';
    $_GET['prm_1'] = self::$params[1];
    $_GET['prm_2'] = isset(self::$params[2]) ? self::$params[2]: 'default';
    $_GET['prm_3'] = self::$params[3];
    $_GET['prm_4'] = self::$params[4];
    $_GET['prm_5'] = self::$params[5];
    if (file_exists('core/modules/' . $_GET['prm_0'] . '/main.php')) {
      require_once 'core/modules/' . $_GET['prm_0'] . '/main.php';
    } else {
      $tpl->content = $eng->msg('2', 'Ошибка, страница не найдена!', '2');
    }
    
  }

Here is the complete class

class router {
  public static $routes = array();
  private static $params = array();
  public static $requestedUrl = '';


  public static function addRoute($route, $destination=null) {
    if ($destination != null && !is_array($route)) {
      $route = array($route => $destination);
    }
    self::$routes = array_merge(self::$routes, $route);
  }

  public static function splitUrl($url) {
    return preg_split('/\//', $url, -1, PREG_SPLIT_NO_EMPTY);
  }
  
  public static function getCurrentUrl() {
    return (self::$requestedUrl?:'/');
  }

  public static function dispatch($requestedUrl = null) {
    if ($requestedUrl == null) {
      //$uri = reset(explode('?', $_SERVER["REQUEST_URI"]));
      $arr = explode('?', $_SERVER["REQUEST_URI"]);
      $uri = reset($arr);
      $requestedUrl = urldecode(rtrim($uri, '/'));
    }

    self::$requestedUrl = $requestedUrl;

    if (isset(self::$routes[$requestedUrl])) {
      self::$params = self::splitUrl(self::$routes[$requestedUrl]);
      return self::executeAction();
    }

    foreach (self::$routes as $route => $uri) {
      if (strpos($route, ':') !== false) {
        $route = str_replace(':any', '(.+)', str_replace(':num', '([0-9]+)', $route));
      }

      if (preg_match('#^'.$route.'$#', $requestedUrl)) {
        if (strpos($uri, '$') !== false && strpos($route, '(') !== false) {
          $uri = preg_replace('#^'.$route.'$#', $uri, $requestedUrl);
        }
        self::$params = self::splitUrl($uri);
            
        break;
      }
    } 
    return self::executeAction();
  } 

  public static function executeAction() {

    $module = isset(self::$params[0]) ? self::$params[0]: 'index';
    $action = isset(self::$params[1]) ? self::$params[1]: 'default';
    
    $params = self::$params[2];
   
   
    $_GET['app'] = $action;
    $_GET['add'] = $params;
    $_GET['param'] = $params;
    $_GET['param_2'] = self::$params[3];
    $_GET['page_name'] = $module;
    
    $_GET['prm_0'] = isset(self::$params[0]) ? self::$params[0]: 'index';
    $_GET['prm_1'] = self::$params[1];
    $_GET['prm_2'] = isset(self::$params[2]) ? self::$params[2]: 'default';
    $_GET['prm_3'] = self::$params[3];
    $_GET['prm_4'] = self::$params[4];
    $_GET['prm_5'] = self::$params[5];

    
    if($_GET['prm_0'] == 'admin') {
      if (file_exists('app/' . $_GET['prm_1'] . '/main.php')) {
        require_once 'app/' . $_GET['prm_1'] . '/main.php';
      } else {
        $tpl->content = $eng->msg('2', 'Ошибка, страница не найдена!', '2');
      }
    } else {
      if (file_exists('core/modules/' . $_GET['prm_0'] . '/main.php')) {
        require_once 'core/modules/' . $_GET['prm_0'] . '/main.php';
      } else {
        $tpl->content = $eng->msg('2', 'Ошибка, страница не найдена!', '2');
      }
    }
  }
}

Answer 1

You have nothing in self::$params, most likely an empty array. Because of this, notices are thrown, which will not lead to a code crash, but which should ideally be fixed. If you have php 7.0+, then in lines like this: $_GET['prm_1'] = self::$params[1]; can be specified like this:
$_GET['prm_1'] = self::$params[1] ?? 'default or false';
If lower, then by analogy with the line: $_GET['prm_0'] = isset(self::$params[0]) ? self::$params[0]: 'index';