public function writeLog($string) {
    $Config = GiroCheckout_SDK_Config::getInstance();
    $path = str_replace('\\', '/', $Config->getConfig('DEBUG_LOG_PATH'));

    if (!is_dir($path)) {
      if (!mkdir($path)) {
        error_log('Log directory does not exist. Please create directory: ' . $path . '.');
      }
      //write .htaccess to log directory
      $htfp = fopen($path . '/.htaccess', 'w');
      fwrite($htfp, "Order allow,deny\nDeny from all");
      fclose($htfp);
    }

    if (!self::$fp) {
      self::$fp = fopen($path . '/' . self::$logFileName, 'a');
      if (!self::$fp) {
        error_log('Log File (' . $path . '/' . self::$logFileName . ') is not writeable.');
      }
    }

    fwrite(self::$fp, $string);
  }