Wordpress Admin Filter : Filter top level pages

index.php

<?php
//defining the filter that will be used to select pages by 'top level pages'
add_action('restrict_manage_posts','add_post_formats_filter_to_post_administration');
function add_post_formats_filter_to_post_administration(){

	//execute only on the 'post' content type
	global $post_type;
	if( $post_type == 'page' ){

		$pages_arg = array(
			'show_option_none'  => 'Toutes les pages',
            		'depth'             => 1,
			'orderby'           => 'NAME',
			'order'             => 'ASC',
			'name'              => 'page_top_pages_admin_filter',
		);

		//if we have a page already selected, ensure that its value is set to be selected
		if( isset($_GET['page_top_pages_admin_filter']) ) {
            		$pages_arg['selected'] = sanitize_text_field($_GET['page_top_pages_admin_filter']);
		}

        	wp_dropdown_pages($pages_arg);

	}
}

// Update the WP Query to properly filter the admin page list
add_action('pre_get_posts','add_post_format_filter_to_posts');
function add_post_format_filter_to_posts($query){

    global $post_type, $pagenow;

    //if we are currently on the edit screen of the post type listings
    if( $pagenow == 'edit.php' && $post_type == 'page' ) {
        if( isset($_GET['page_top_pages_admin_filter']) ) {

            //get the desired page
            $page = sanitize_text_field($_GET['page_top_pages_admin_filter']);

            if( $page != 0 ) {
                $query->query_vars['page_id'] = $page;
            }
        }
    }
}

Goal : The goal of this gist is to only show top level pages in a wordpress website with a lot of subpages.

TODO : Improve the dropdown to filter by depth level and not root pages directly