Working on a client site I've encounter my worst enemy... WP URL rewrite :(.
I actually can't figure it out and after many days trying and searching, I can't make it work. 

What I'm trying to get is a permalink like this `company.com/product/%product-name%/` regardless of the `/parent/child/` nesting depth. I do need the functionalities of the hierarchical pages for other reasons, but it should not appear in the URL.

Here is my set up:

* Wordpress 4.4.1
* Permalink settings set to `Post name`

* I created a hierarchical custom post type `product` with rewrite parameter to false.

        $args = array(
        	'label'                 => __( 'Product', 'domain' ),
    	    'description'           => __( 'Company products', 'domain' ),
    	    'labels'                => $labels,
        	'supports'              => array( 'title', 'editor', 'excerpt', 'thumbnail', 'revisions', 'page-attributes' ),
	        'taxonomies'            => array( 'category', 'post_tag' ),
	        'hierarchical'          => true,
	        'public'                => true,
	        'show_ui'               => true,
	        'show_in_menu'          => true,
	        'menu_position'         => 5,
	        'show_in_admin_bar'     => true,
	        'show_in_nav_menus'     => false,
	        'can_export'            => true,
	        'has_archive'           => true,
	        'exclude_from_search'   => false,
	        'publicly_queryable'    => true,
	        'rewrite'               => false,
	        'capability_type'       => 'page',
        );
        register_post_type( 'product', $args );

At this point the products don't have a pretty permalink,
they look like this and they both work:

 1. First level: `company.com/?product=my-first-product` -> ok
 2. Second level: `company.com/?product=my-first-product/child-product` -> ok


After that, I registered the rewrite rule and permastruct then flushed the rewrite rules by saving changes in the permalink settings page
         
        function bvt_product_rewrite_rule() {
        	add_rewrite_rule( 
                '^product/([^/]+)/?$',
                'index.php?post_type=product&pagename=$matches[1]',
                'top'
	        );
	        add_permastruct( 'product', '/product/%product%/' );
        }
        add_action( 'init', 'bvt_product_rewrite_rule', 10 );

Now the permalinks where correctly displayed for first level page but not correct for child page. Also both levels gave me a 404 error.

 1. First Level: `company.com/product/my-first-product/` -> 404
 2. Second Level: `company.com/product/my-first-product/child-product/` -> 404

I also tried a solution given here http://wordpress.stackexchange.com/a/101077/86838 where it allowed to remove the parent slug from child permalink, but I was still unsuccessful

    function bvt_product_flatten_hierarchies( $post_link, $post ) {
	    if ( 'product' != $post->post_type ) {
            return $post_link;
		}

        $uri = '';
        foreach ( $post->ancestors as $parent ) {
            $uri = get_post( $parent )->post_name . "/" . $uri;
        }

        return str_replace( $uri, '', $post_link );
    }
    add_filter( 'post_type_link', 'bvt_product_flatten_hierarchies', 10, 2 );

I installed two plugins **debug-bar** and **monkeyman-rewrite-analyzer** to analyse the rewrite and query, but I keep can't make it work.

My last try was with **wp-permastructure** plugin with allow to set custom permalink to custom post type. Which enables the custom setting `permastruct` in the `rewrite` array option of the `register_post_type`.

    [...]
    'publicly_queryable'    => true,
	'rewrite'               => array(
        'permastruct'	=> '/%postname%/',
	),
	'capability_type'       => 'page',
    [...]

With this setting and both previous custom rewrite/permatruct/flatten_hierarchies desabled, it worked as stated by the plugin description

 1. First Level:      `company.com/my-first-product/` -> ok
 2. Second Level: `company.com/child-product/` -> ok

But now the `/product/` level is missing, and if I try to put it in the `'permastruct' => '/product/%postname%/'` config it brings me back to both a 404 error.

Which leads to my main question.

Is it possible to do what I need to or only as close as I could go with the latest plugin ?

Thanks already for anybody who will take the time to answer me, and maybe save me from my poor situation.
Thanks

PS I can't insert more than two links in the body so here is the mentioned plugin links:

    https://wordpress.org/plugins/debug-bar/
    https://wordpress.org/plugins/monkeyman-rewrite-analyzer/
    https://wordpress.org/plugins/wp-permastructure/