WP rewrite permalinks for custom post type

/**
 * Get 'Training' custom post type meta info group variables.
 *
 * @uses get_post_meta()
 * @uses esc_attr()
 */
function tr2014_get_training_first_date( $post ) {
    $options = get_post_meta( $post->ID, '_tr_training_option_group', true );

    $date_start = false;
    foreach ( (array) $options as $key => $option ) {
        if ( !empty( $option['_tr_training_date_start'] ) ) {
            $date_start = strtotime( $option['_tr_training_date_start'] );
            break;
        }
    }

    return $date_start;
}

/**
 * Create custom post types for 'Training'
 */
function tr2014_create_post_types() {
    register_post_type( 'tr_training',
        array(
            'labels' => array(
                'name'                  => __( 'Trainingen', 'tr2014' ),
                'singular_name'         => __( 'Training', 'tr2014' ),
                'add_new'               => __( 'Nieuwe training', 'tr2014' ),
                'add_new_item'          => __( 'Nieuwe training toevoegen', 'tr2014' ),
                'edit_item'             => __( 'Wijzig training', 'tr2014' ),
                'new_item'              => __( 'Nieuwe training toevoegen', 'tr2014' ),
                'view_item'             => __( 'Training bekijken', 'tr2014' ),
                'search_items'          => __( 'Trainingsaanbod doorzoeken', 'tr2014' ),
                'not_found'             => __( 'Geen trainingen gevonden.', 'tr2014' ),
                'not_found_in_trash'    => __( 'Geen trainingen gevonden in Prullenbak.', 'tr2014' ),
                'all_items'             => __( 'Alle trainingen', 'tr2014' )
            ),
            'public'                => true,
            'query_var'             => true,
            'rewrite'               => false,
            'menu_position'         => 25,
            'menu_icon'             => 'dashicons-groups',
            'capability_type'       => 'page',
            'supports'              => array( 'title', 'editor', 'excerpt', 'thumbnail', 'custom_fields' ),
        )
    );
}
add_action( 'init', 'tr2014_create_post_types' );


/**
 * Properly replace custom post type(s) permalinks.
 */
function tr2014_post_type_link( $url, $post, $leavename = false ) {

    if ( !is_single() && get_post_type( $post ) == 'tr_training' ) {
        $new_url = $url;

        $re_search = array(
            '%startdate%',
            $leavename ? '' : '%postname%',
            '%post_id%',
            $leavename ? '' : '%pagename%',
        );

        $date_start = tr2014_get_training_first_date( $post );

        if ( !empty( $url ) && !in_array( $post->post_status, array('draft', 'pending', 'auto-draft') ) ) {
            if ( $date_start ) {
                // Append start date to permalink, if it exists
                $new_url .= '/%startdate%';
            }

            // Replace %startdate% with formatted date, e.g. "2014-12-23"
            $re_replace = array(
                ( $date_start ? date( 'Y-m-d', $date_start ) : ''),
                $post->post_name,
                $post->ID,
                $post->post_name,
            );
            $new_url = str_replace( $re_search, $re_replace, $new_url );
        } else {
            // Not using rewrite/permalink option
        }
    }

    return $new_url;
}
add_filter( 'post_type_link', 'tr2014_post_type_link', 10, 2 );


/**
 * Add support for %startdate% tag in permalinks.
 */
function tr2014_rewrite_tags() {
    //add_rewrite_tag( '%startdate%', '([0-9]{4}-[0-9]{2}-[0-9]{2})$', 'startdate=' );
    //add_permastruct( 'tr_training', '/trainings/%postname%/%startdate%', false );
    add_rewrite_tag( '%training%', '([^/]+)(/.*)$', 'tr_training=' );
    add_rewrite_tag( '%startdate%', '([^/]+)(/.*)$', 'tr_training=' );
    add_permastruct( 'tr_training', '/trainings/%training%/%startdate%', false );
    //add_rewrite_tag( '%postname%', '([^/]+)', 'tr_training=' );
    //add_permastruct( 'tr_training', '/trainings/%postname%', false );
}
add_action( 'init', 'tr2014_rewrite_tags', 10, 0 );