public function trackEvent($category, $action, $label = null, $value = null)
    {
        $command = '';
        if ($label !== null) {
            $command .= ", '{$label}'";
            if ($value !== null && is_numeric($value)) {
                $command .= ", {$value}";
            }
        }

        $trackingCode = "ga('send', 'event', '{$category}', '{$action}'$command);";

        $this->trackingBag->add($trackingCode);
    }