guest author latest post

gistfile1.php

/**
 * Add the most recent post id to each guest author as meta
 */
function time_guest_author_latest_post( $post_id, $post ) {

	if( $post->post_type == 'post' ) {
		
		$guest_id = get_post_meta( $post_id, 'time_guest_author', true );

		if( $guest_id ) {

			// get the guests most recent post id
			$latest_post_id = get_post_meta( $guest_id, 'time_latest_post_id', true );

			if( ( $latest_post_id && $post_id > $latest_post_id ) || !$latest_post_id ) {
				update_post_meta( $guest_id, 'time_latest_post_id', $post_id );
			}
		}
	}
}
add_action( 'save_post', 'time_guest_author_latest_post', 97, 2 );