Add Facebook Open Graph Meta Tags

functions.php

/* ---------------------------------------------------------------------------
 * FACEBOOK OPENGRAPH SETTINGS
 * ---------------------------------------------------------------------------
 * @wp-filter - language_attributes
 * @retun - adds og lang tags to doc element
 * 
 * @wp-hook wp_head
 * @return - adds og meta tags to pages
 * --------------------------------------------------------------------------- */
add_filter('language_attributes', 'tda_doctype_opengraph');
function tda_doctype_opengraph($output) {
    return $output . '
    xmlns:og="http://opengraphprotocol.org/schema/"
    xmlns:fb="http://www.facebook.com/2008/fbml"';
}

add_action('wp_head', 'tda_fb_opengraph', 5);
function tda_fb_opengraph() {
    global $post;
    
    //$date = date("Y-m-d");
    //$time = time();
 
    if(is_single() || is_front_page()) {
        if(has_post_thumbnail($post->ID)) {
            $img_src = wp_get_attachment_image_src(get_post_thumbnail_id( $post->ID ), 'medium');
        } else {
            $img_src = 'http://thedeviantadvantagebook.com/wp-content/uploads/2014/09/sandi-speaks.jpg';
        }
        if($excerpt = $post->post_excerpt) {
            $excerpt = strip_tags($post->post_excerpt);
            $excerpt = str_replace("", "'", $excerpt);
        } else {
            $excerpt = get_bloginfo('description');
        }
        ?>
 
    <meta property="og:title" content="<?php echo the_title(); ?>"/>
    <meta property="og:description" content="<?php echo $excerpt; ?>"/>
    <meta property="og:type" content="article"/>
    <meta property="og:url" content="<?php echo the_permalink(); ?>?"/>
    <meta property="og:site_name" content="<?php echo get_bloginfo(); ?>"/>
    <meta property="og:image" content="<?php echo $img_src; ?>"/>
 
<?php
    } else {
        //return;
        ?>
            <! -- no fb meta output -->
        <?php
    }
}