private function lookup_message_variables($matches) {
        $options = array(
                'operation' => $this->type,
                'backupid' => $this->backupid,
                'user_username' => $this->user->username,
                'user_email' => $this->user->email,
                'user_firstname' => $this->user->firstname,
                'user_lastname' => $this->user->lastname,
                'link' => $this->get_resource_link(),
        );

        $match = $options[$matches[1]] ?? $matches[1];

        return $match;
    }