Post Slug as ID

<?php
/*
Plugin Name: Post Slug as ID
*/

add_filter('post_type_link', 'cpt_type_link', 1, 3);

function cpt_type_link($url, $post = null, $leavename = false)
{
    $tag = '%post_id%';

    if ($post->post_type != 'mycpt') {
        return $url;
    }

    $post_id = $post->ID;

    // replace tag with the slug: /youcpt/1234
    return str_replace($tag, $post_id, $url);
}


function cpt_add_rewrite_rules()
{
    global $wp_rewrite;

    register_post_type('mycpt', array(
        'name' => 'My Custom type',
        'label' => 'Slug as ID',
        'public' => true,
        'has_archive' => true,
        'rewrite' => array('slug' => 'products'),
        'query_var' => true // ....
        )
    );

    $wp_rewrite->extra_permastructs['mycpt'][0] = "/products/%post_id%";

    add_rewrite_rule("products/?$", 'index.php?post_type=mycpt', 'top');
    add_rewrite_rule("products/([0-9]{1,})/?$", 'index.php?post_type=mycpt&p=$matches[1]', 'top');
    add_rewrite_rule("products/([0-9]{1,})/page/([0-9]{1,})/?$", 'index.php?post_type=mycpt&p=$matches[1]&paged=$matches[2]', 'bottom');

    flush_rewrite_rules(); // call just on plugin activation
}

add_action('init', 'cpt_add_rewrite_rules');