public function log(
        $message,
        $priority = Net_Notifier_Logger::VERBOSITY_MESSAGES,
        $timestamp = true
    ) {
        if ($priority <= $this->verbosity) {
            $message = ($timestamp)
                ? '[' . date('Y-m-d H:i:s') . '] ' . $message
                : $message;

            if ($priority === Net_Notifier_Logger::VERBOSITY_ERRORS) {
                $this->outputter->stderr($message);
            } else {
                $this->outputter->stdout($message);
            }
        }

        return $this;
    }