protected function _renderHead()
    {
        $document = $this->getService('anahita:document');
        $html = '<base href="base://" />';
        $html .= '<title>'.$document->getTitle().'</title>';
        $html .= '<meta name="description" content="'.$document->getDescription().'" />';

        /* Google+ Card*/
        $html .= '<meta itemprop="name" content="'.$document->getTitle().'" />';
        $html .= '<meta itemprop="description" content="'.$document->getDescription().'" />';

        if ($document->getImage()) {
            $html .= '<meta itemprop="image" content="'.$document->getImage().'" />';
        }

        /* Twitter Card */
        $twitter_card = ($document->getImage()) ? 'summary_large_image' : 'summary';
        $html .= '<meta name="twitter:card" value="'.$twitter_card.'">';
        $html .= '<meta property="twitter:title" content="'.$document->getTitle().'" />';
        $html .= '<meta property="twitter:description" content="'.$document->getDescription().'" />';
        $html .= '<meta property="og:type" content="'.$document->getType().'" />';
        $html .= '<meta property="twitter:site" content="'.$document->getLink().'" />';

        if ($document->getImage()) {
            $html .= '<meta property="twitter:image:src" content="'.$document->getImage().'" />';
        }


        /* Generic Open Graph tags */
        $html .= '<meta property="og:title" content="'.$document->getTitle().'" />';
        $html .= '<meta property="og:description" content="'.$document->getDescription().'" />';
        $html .= '<meta property="og:type" content="'.$document->getType().'" />';
        $html .= '<meta property="og:url" content="'.$document->getLink().'" />';

        if ($document->getImage()) {
            $html .= '<meta property="og:image" content="'.$document->getImage().'" />';
        }

        return $html;
    }