Add Open Graph tags to your WordPress site

akorg-open-graph.php

<?php
/**
 * Plugin Name: AK.org Strict Open Graph Tags
 * Description: Add Open Graph tags so that Facebook (and any other service that supports them) can crawl the site better and we provide a better sharing experience
 * Author: Automattic and Alex King
 * License: GPLv2, baby!
 *
 * @link http://ogp.me/
 * @link http://developers.facebook.com/docs/opengraph/
 */

add_action( 'wp_head', 'wpcom_og_tags' );

function wpcom_og_tags() {
	$og_output = '';
	$tags = array();
	
	$image_width = 300;
	$image_height = 300;
	$description_length = 197;
	
	if ( is_home() || is_front_page() ) {
		$site_type = get_option( 'open_graph_protocol_site_type' );
		$tags['og:type'] = ! empty( $site_type ) ? $site_type : 'blog';
		
		$tags['og:title'] = get_bloginfo( 'name' );
		$tags['og:url'] = home_url();
		$tags['og:description'] = get_bloginfo( 'description' );
		
		// Associate a blog's root path with one or more Facebook accounts
		$facebook_admins = get_option( 'facebook_admins' );
		if ( ! empty( $facebook_admins ) )
			$tags['fb:admins'] = $facebook_admins;
		
	}
	else if ( is_author() ) {
		$tags['og:type'] = 'author';
	
		$author = get_queried_object();
	
		$tags['og:title'] = $author->display_name;
		$tags['og:url'] = get_author_posts_url( $author->ID );
		$tags['og:description'] = $author->description;
	
	}
	else if ( is_singular() ) {
		$tags['og:type'] = 'article';

		$tags['og:title'] = get_the_title();
		$tags['og:url'] = get_permalink();

		$tags['og:description'] = strip_tags( get_the_excerpt() );
	}
	
	if ( empty( $tags ) )
		return;
	
	$tags['og:site_name'] = get_bloginfo( 'name' );
	
	$tags['og:image'] = wpcom_og_get_image();
	
	// Facebook whines if you give it an empty title
	if ( empty( $tags['og:title'] ) )
		$tags['og:title'] = __( '(no title)' );
	
	// Shorten the description if it's too long
	$tags['og:description'] = strlen( $tags['og:description'] ) > $description_length ? substr( $tags['og:description'], 0, $description_length ) . '...' : $tags['og:description'];

	$tags = apply_filters( 'wpcom_open_graph_tags', $tags );
	
	foreach ( (array) $tags as $tag_property => $tag_content ) {
		foreach( (array) $tag_content as $tag_content_single ) { // to accomodate multiple images			
			$og_output .= sprintf( '<meta property="%s" content="%s" />', esc_attr( $tag_property ), esc_attr( $tag_content_single ) );
			$og_output .= "\n";
		}
	}
	
	echo $og_output; 
}

function wpcom_og_get_image() { // Facebook requires thumbnails to be a minimum of 50x50
	$image = '';
	
	if ( is_singular() ) {
		$size = apply_filters('ak_og_img_size', 'medium');
		
		// If a featured image is set, use that
		if( function_exists( 'has_post_thumbnail' ) && has_post_thumbnail() ) {
			$image_src = wp_get_attachment_image_src( get_post_thumbnail_id(), $size );
			$image = $image_src[0];
		}
		
	}
	else if ( is_author() ) {
		$author = get_queried_object();
		$avatar = get_avatar_url( $author->user_email, 100 );
		
		if ( ! empty( $avatar ) )
			$image = $avatar[0];
	}

	// Fallback to default
	if ( empty( $image ) ) {
		$url = apply_filters('ak_og_default_img', trailingslashit(get_stylesheet_directory_uri()).'og-image.png');
		$image = $url;
	}
		
	return $image;
}