protected function generateCSV()
    {
        $str = "msisdn,message";

        foreach ($this->messages as $message) {
            $str .= "\n";
            $recipient = $message->getRecipient();
            $message   = $message->getMessage();
            $str .= '"' . $recipient . '","' . $message . '"';
        }

        return $str;
    }