Pinterest image functions

front-end-display.php

<?php if ( $image = zdt_get_social_image( $post ) ) : ?>
	<div class="pin_share">
		<a href="http://pinterest.com/pin/create/button/?url=<?php echo urlencode( esc_url( get_the_permalink( get_the_ID() ) ); ?>&media=<?php echo urlencode( esc_url( $image ) ); ?>&description=<?php echo urlencode( esc_html( get_the_excerpt( get_the_ID() ) ); ?>" class="pin-it-button" count-layout="none">Pin It</a>
	</div>
<?php endif; ?>

image-functions.php

<?php
/**
 * Get the image for use with social media when status is transitioned.
 *
 * @param $new_status
 * @param $old_status
 * @param $post
 */
function zdt_save_social_image( $new_status, $old_status, $post ) {
	if ( $post->post_type == 'post' && $new_status == 'publish' ) {
		update_post_meta( $post->ID, '_zdt_social_image', zdt_determine_first_image( $post, 'http://placehoneybadger.com/g/200/300' ) );
	}
}
add_action( 'transition_post_status', 'zdt_save_social_image', 10, 3 );

/**
 * Get the first image for the post.
 *
 * If there are any attachments associated with the post, get the first attachment and use that.
 * Unfortunately, not all posts use an attachment related to the post. In this case, use the DOMDocument
 * parser to find the first image in the post content and use that. If all else fails, use the default image
 * sent to the function.
 *
 * @param $post
 * @param bool|string $default
 * @return string
 */
function zdt_determine_first_image( $post, $default = false ) {
	if ( is_object( $post ) )
		$post_id = $post->ID;
	else
		return esc_url( $default );

	// Start by getting an attached image
	$attachments = new WP_Query( array( 'post_parent' => $post_id, 'post_type' => 'attachment', 'post_status' => 'inherit', 'posts_per_page' => 1, 'orderby' => 'menu_order' ) );

	if ( $attachments->have_posts() ) {
		$id = $attachments->posts[0]->ID;
		wp_reset_query();

		if ( $image = wp_get_attachment_image_src( $id, 'medium' ) ) {
			return esc_url( $image[0] );
		}
	}

	// Provide our own error handling in the event that parse errors occur
	libxml_use_internal_errors( true );

	// No attachments, so try grabbing the first image from the content
	$doc = new DOMDocument;
	if ( ! empty( $post->post_content ) && $doc->loadHTML( $post->post_content ) ) {

		/**
		 * Detect fatal errors. In many cases, "simple" or "recoverable" errors may be thrown when parsing the HTML (http://www.xmlsoft.org/html/libxml-xmlerror.html).
		 * For instance, if two element have the same ID, an error of level 2 will be thrown. This is ok for our purposes; however, if a fatal
		 * error (level 3) is thrown, we should not attempt to do anything else with the object.
		 */
		$fatal_error = false;
		foreach (libxml_get_errors() as $error) {
			if ( $error->level > 2 )
				$fatal_error = true;
		}

		if ( ! $fatal_error ) {
			$images = $doc->getElementsByTagName( 'img' );

			if ( $images && $images->length > 0 && $images->item(0)->hasAttribute( 'src' ) ) {
				$img_src = $images->item(0)->getAttribute( 'src' );
				return esc_url( $img_src );
			}
		}
	}
	libxml_clear_errors();

	return esc_url( $default );
}

/**
 * Attempts to get image for social media.
 *
 * In the event that it is not already set, the image is obtained, saved and displayed.
 *
 * @param $post
 * @param bool $default
 * @return mixed|string
 */
function zdt_get_social_image( $post, $default = false ) {
	if ( $image = get_post_meta( $post->ID, '_zdt_social_image', true ) )
		return $image;
	else {
		$image = zdt_determine_first_image( $post, $default );
		update_post_meta( $post->ID, '_zdt_social_image', $image );
		return $image;
	}
}