Update Custom Terms

<?php
/**
 * Update Custom Terms
 *
 * @author     Fred Bradley <@fredbradley>
 * @version    1.0
 * @since      Since Release 1.0.0
 */
function update_station_tag_list($post_id) {
 
    // only update terms if it's a post-type-B post
    if ( 'station' != get_post_type($post_id)) {
        return;
    }
 
    // don't create or update terms for system generated posts
    if (get_post_status($post_id) == 'auto-draft') {
        return;
    }
    
    /*
    * Grab the post title and slug to use as the new 
    * or updated term name and slug
    */
    $term_title = get_the_title($post_id);
    $term_slug = get_post( $post_id )->post_name;
 
    $debug = wp_set_post_terms( $post_id, $term_title, 'post_tag', true );
	if ( is_wp_error( $debug ) ) {
		$error_string = $debug->get_error_message();
		return '<div id="message" class="error"><p>' . $error_string . '</p></div>';
	}

    /*
    * Check if a corresponding term already exists by comparing 
    * the post ID to all existing term descriptions. 
    */
    $existing_terms = get_terms('post_tag', array(
        'hide_empty' => false
        )
    );
 
    foreach($existing_terms as $term) {
        if ($term->description == $post_id) {
            //term already exists, so update it and we're done
            wp_update_term($term->term_id, 'post_tag', array(
                'name' => $term_title,
                'slug' => $term_slug
                )
            );
            return;
        }
    }
 
    /* 
    * If we didn't find a match above, this is a new post, 
    * so create a new term.
    */
    wp_insert_term($term_title, 'post_tag', array(
        'slug' => $term_slug,
        'description' => $post_id
        )
    );
    

}
//run the update function whenever a post is created or edited
add_action('save_post', 'update_station_tag_list');