Add dates to permalink structure

<?php
/*
 * Add the start event date in the permalink using the format /YYYY/mm/dd
 * Inspired by http://pastebin.com/v4fT1671
 * For installation instructions, see this tutorial, we recommend adding this to mu-plugins as a separate file:
 * http://wp-events-plugin.com/tutorials/how-to-safely-add-php-code-to-wordpress/
 */

/**
 * Add the start event date in the permalink
 *
 * @param string $permalink Permalink
 * @param object $post Post object
 * @param boolean $leavename
 * @return string Permalink
 */
function my_events_manager_get_permalink($permalink, $post, $leavename = false)
{
    if ($post->post_type == 'event') {
        $event = em_get_event($post->ID, 'post_id');
        $start_date = $event->event_start_date;
        $start_date = str_replace('-', '/', $start_date);
        $event_slug = get_site_option('dbem_cp_events_slug');
        $permalink = str_replace($event_slug, $event_slug . '/' . $start_date, $permalink);
        return $permalink;
    } else
        return $permalink;
}
add_filter('post_type_link', 'my_events_manager_get_permalink', 10, 3);

/**
 * Add a rewrite rule to accept the date in the permalink
 */
function my_events_manager_add_rules() {
    $event_slug = get_site_option('dbem_cp_events_slug');
    add_rewrite_rule($event_slug . '/\d+/\d+/\d+/(.+)$', 'index.php?post_type=event&name=$matches[1]', 'top'); // single event
}
add_action('init', 'my_events_manager_add_rules', 9); // Must be run before events manager