Redirect old slugs

function pm_detect_old_slugs() {
    global $wp_query, $wp, $wpdb;

    // Stop if any post or term was already found by Permalink Manager
    if(!empty($wp_query->query['do_not_redirect']) || !empty($wp_query->query_vars['do_not_redirect']) || (!is_404())) {
        return;
    }

    // Get the string from URL
    preg_match('/([^\/]+)(?:\/([\d]+))?/', $wp->request, $parts);
    if(!empty($parts[1])) {
        $post_id = $wpdb->get_var($wpdb->prepare("SELECT post_id from {$wpdb->postmeta} WHERE meta_key = '_wp_old_slug' AND meta_value LIKE '%%%s%%'", $parts[1]));

        // Redirect if post with old slug was found
        if(!empty($post_id)) {
            $permalink = get_permalink($post_id);
            $permalink = (!empty($parts[2])) ? sprintf('%s/%d', trim($permalink, '/'), $parts[2]) : '';

            wp_safe_redirect($permalink, 301);
            exit();
        }
    }
}
add_action('template_redirect', 'pm_detect_old_slugs', 0);