Websites/webkit.org/wp-content/plugins/social-meta.php

<?php
/*
Plugin Name: Social Meta
Description: Adds schema.org, Twitter Card, Open Graph meta for posts and pages
Version:     1.0
Author:      Jonathan Davis
Author URI:  http://webkit.org
*/

add_action('wp_head', function() {

    $title = the_title_attribute('echo=0');
    $description = get_the_excerpt();
    $type = 'article';
    $url = get_the_permalink();
    $categories = array();
    $tags = array();
    $twitter_handle = '';
    $published_time = '';
    $modified_time = '';

    $fb_admins = array(
        'Jon Davis' => '1085088865'
    );

    if (is_front_page()) { // Landing page
        $title = get_bloginfo('name');
        $description = get_bloginfo('description');
        $type = 'website';
    } elseif (is_home()) { // Blog "page"
        $title = get_bloginfo('name');
        $description = "A collection of all " . get_bloginfo('name') . " blog posts.";
        $type = 'website';
        $url = get_home_url(null, '/blog/');
    } elseif (is_post_type_archive()) { // custom post type archive "page"
        $post_type = get_post_type();
        $post_type_archive_url = get_post_type_archive_link($post_type);
        $type = 'website';
        $title = post_type_archive_title('', false);
        $post_type_obj = get_post_type_object($post_type);
        if (isset($post_type_obj->description))
            $description = $post_type_obj->description;
        if (!empty($post_type_archive_url))
            $url = $post_type_archive_url;
    } elseif (is_archive()) { // archives and category "pages"
        $type = 'website';
        $title = get_bloginfo('name')." Blog ".get_the_archive_title();
        $description = "A collection of " . get_bloginfo('name') . " blog posts.";
        if (is_category()) {
            $category_objects = get_the_category();
            if (isset($category_objects[0]->term_id))
                $url = get_category_link($category_objects[0]->term_id);
        }
    } elseif (is_single() || is_page()) { // Posts and Pages
        $post = get_post();
        $social_image_url = get_post_meta(get_the_ID(), 'og-image-url', true);
        if (!empty($social_image_url)) {
            $image_url = $social_image_url;
        } elseif (has_post_thumbnail()) {
            $image_src = wp_get_attachment_image_src(get_post_thumbnail_id($post_id), 'large');
            if (isset($image_src[0]))
                $image_url = $image_src[0];
        } elseif (is_single()) {
            preg_match_all('/<img.+src(set)?=[\'"]([^\s\'"]+).*[\'"].*>/i', $post->post_content, $matches);
            if (isset($matches[2][0]))
                $image_url = $matches[2][0];
        }
        $categories = wp_get_object_terms(get_the_ID(), 'category', array('fields' => 'names'));
        $tags = wp_get_object_terms(get_the_ID(), 'post_tag', array('fields' => 'names'));

        // Post author data is not available in wp_head filter context
        $twitter_handle = get_the_author_meta('twitter', $post->post_author);
        $published_time = get_the_time('c');
        $modified_time = get_the_modified_date('c');
    }

    if ($image_url[0] === '/')
        $image_url = get_home_url(null, $image_url);
?>

    <!-- Schema.org markup -->
    <meta itemprop="name" content="<?php echo esc_attr($title); ?>">
<?php if ($description): ?>
    <meta itemprop="description" content="<?php echo esc_attr($description); ?>">
<?php endif; ?>
<?php if ($image_url): ?>
    <meta itemprop="image" content="<?php echo esc_url($image_url); ?>">
<?php endif; ?>

    <!-- Twitter Card data -->
<?php if ($image_url): // Twitter summary card with large image must be at least 280x150px ?>
    <meta name="twitter:card" content="summary_large_image">
    <meta name="twitter:image:src" content="<?php echo esc_url($image_url); ?>">
<?php endif; ?>
    <meta name="twitter:site" content="@webkit">
    <meta name="twitter:title" content="<?php echo esc_attr($title); ?>">
<?php if ($description): ?>
    <meta name="twitter:description" content="<?php echo esc_attr($description); ?>">
<?php endif; ?>
<?php if ($twitter_handle): ?>
    <meta name="twitter:creator" content="@<?php echo esc_attr($twitter_handle); ?>">
<?php endif; ?>

    <!-- Open Graph data -->
    <meta property="og:title" content="<?php echo esc_attr($title); ?>">
    <meta property="og:type" content="<?php echo esc_attr($type); ?>">
    <meta property="og:url" content="<?php echo esc_url($url); ?>">
<?php if ($image_url): ?>
    <meta property="og:image" content="<?php echo esc_url($image_url); ?>">
<?php endif; ?>
<?php if ($description): ?>
    <meta property="og:description" content="<?php echo esc_attr($description); ?>">
<?php endif; ?>
    <meta property="og:site_name" content="<?php bloginfo('title'); ?>">
<?php if ($published_time): ?>
    <meta property="article:published_time" content="<?php echo $published_time; ?>">
<?php endif; ?>
<?php if ($modified_time): ?>
    <meta property="article:modified_time" content="<?php echo $modified_time; ?>">
<?php endif; ?>
<?php
    if (!empty($categories)):
        $section = array_shift($categories);      // The first category is used as the section
        $tags = array_merge($categories, $tags);  // The rest are prepended to the tag list
?>
    <meta property="article:section" content="<?php echo esc_attr($section); ?>">
<?php
    endif;

    if (!empty($tags)):
        foreach($tags as $tag):
?>
    <meta property="article:tag" content="<?php echo esc_attr($tag); ?>">
<?php
        endforeach;
    endif;

    if (!empty($fb_admins)):
        foreach($fb_admins as $id):
?>
    <meta property="fb:admins" content="<?php echo esc_attr($id); ?>">
<?php
        endforeach;
    endif;
});