Old posts format fallback

<?php
/*
* Plugin Name:       Post Permalinks Fallback
* Plugin URI:        http://maciejbis.net/
* Description:       Plugin that allows to keep old permalinks format (%post_id%/%postname%)
* Version:           1.0.0
* Author:            Maciej Bis
* Author URI:        http://maciejbis.net/
* License:           GPL-2.0+
* License URI:       http://www.gnu.org/licenses/gpl-2.0.txt
* Domain Path:       /languages
*/

class Bis_Post_Permalinks_Fallback {
    function __construct() {
        add_action('init', array($this, 'init'));

        register_activation_hook(__FILE__, array($this, 'flush_rewrite_rules'));
        register_deactivation_hook(__FILE__, array($this, 'flush_rewrite_rules'));
    }

    function init() {
        add_filter('post_link', array($this, 'filter_post_permalinks'), 999, 2);
        add_action('init', array($this, 'extra_post_permastructs'), 100);
        add_action('admin_init', array($this, 'limit_date_settings'));
    }

    /**
     * Filter post permalinks
     */
    function filter_post_permalinks($url, $element) {
        $limit_date = get_option('bis_permalink_limit_date');

        // Posts permalinks added after the date provided below will not be changed
        if(!empty($limit_date) && strtotime($element->post_date) >= strtotime($limit_date)) {
            return $url;
        }

        if(!empty($element->post_type) && $element->post_type == 'post') {
            $url = sprintf('%s/%d/%s', rtrim(get_home_url()), $element->ID, $element->post_name);
        }

        return user_trailingslashit($url);
    }

    /**
     * Register new additional set of rewrite rule for old post permalinks
     * %post_id%/%postname%
     */
    function extra_post_permastructs() {
        add_permastruct('post-old-format', '%post_id%/%postname%', array('with_front' => false));
    }

    /**
     * Flush rewrite rules during plugin activation
     */
    function flush_rewrite_rules() {
        flush_rewrite_rules();
    }

    /**
     * Display extra field in "Permalinks" admin section
     */
    function limit_date_settings() {
      add_settings_field(
        'bis_permalink_limit_date',
        'Old post permalinks limit date',
        array($this, 'limit_date_field'),
        'permalink',
        'optional',
        array('label_for' => 'bis_permalink_limit_date')
      );

        if(isset($_POST['bis_permalink_limit_date'])) {
            update_option('bis_permalink_limit_date', sanitize_title_with_dashes($_POST['bis_permalink_limit_date']));
        }

    }

    function limit_date_field($args) {
        $value = get_option('bis_permalink_limit_date', '2019-03-01');

        printf('<input type="text" value="%s" name="bis_permalink_limit_date" id="bis_permalink_limit_date" class="regular-text" />', esc_attr($value));
    }

}
new Bis_Post_Permalinks_Fallback();