public function facebookShareUrl($url = null, $text = null) {
        $shareUrl = is_null($url) ? $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] : $url;
        $url = 'http://facebook.com/sharer.php?u=' . urlencode($shareUrl);
        if (!is_null($text)) {
            $url .= '&t=' . $text;
        }
        return $url;
    }