protected function getContentType($type, $version)
    {
        if ($type === 'css') {
            return 'text/css';
        } else if ($type === 'js') {
            return 'text/javascript';
        } else if ($type === 'image') {
            $fileExtension = pathinfo($version, PATHINFO_EXTENSION);
            
            if ($fileExtension === 'svg') {
                return 'image/svg+xml';
            } else if ($fileExtension === 'jpg') {
                return 'image/jpeg';
            } else if ($fileExtension === 'gif') {
                return 'image/gif';
            } else if ($fileExtension === 'png') {
                return 'image/png';
            }
        }
    }