One-time autogenerate a menu from WordPress page structure

wordpress_create_menu_from_page_structure.php

<?php

/**
 * Generate a menu with content and hierarchy that match the page structure.
 * Trigger with ?autogenerate=true in the URL; note that it won't update a menu, so you'll need to delete and recreate if necessary.
 *
 * @return void
 */
function yoko_child_theme_create_menu_from_page_structure() {
	$menu_name = 'Auto-generated menu from page structure';
	$post_type = 'page';

	if (
		! empty( $_GET['autogenerate'] ) &&
		'true' === $_GET['autogenerate']
	) {
		// Does the menu exist already? We don't want to overwrite a menu.
		$menu_exists = wp_get_nav_menu_object( $menu_name );

		// If it doesn't exist, let's create it.
		if ( ! $menu_exists ) {
			$menu_id = wp_create_nav_menu( $menu_name );

			$pages_to_add = get_posts(
				array(
					'numberposts' => -1,
					'orderby'     => 'menu_order',
					'order'       => 'ASC',
					'post_type'   => $post_type,
				)
			);

			if ( ! empty( $pages_to_add ) ) {

				// We have to loop through them somewhat carefully to ensure that the parents are created before their children.
				$valid_parent_ids = array( 0 );
				$new_menu_obj     = array();
				do {
					$skipped_pages = 0;

					foreach ( $pages_to_add as $index => $page_to_add ) {
						if ( in_array( $page_to_add->post_parent, $valid_parent_ids, true ) ) {
							$new_menu_obj[ $page_to_add->ID ] = array();
							$new_menu_obj[ $page_to_add->ID ]['menu-item'] = wp_update_nav_menu_item(
								$menu_id,
								0,
								array(
									'menu-item-title'     => $page_to_add->post_title,
									'menu-item-object'    => $post_type,
									'menu-item-parent-id' => $new_menu_obj[ $page_to_add->post_parent ]['menu-item'],
									'menu-item-object-id' => $page_to_add->ID,
									'menu-item-type'      => 'post_type',
									'menu-item-status'    => 'publish',
								)
							);

							if (
								empty( $new_menu_obj[ $page_to_add->post_parent ]['menu-item'] ) &&
								! empty( $page_to_add->post_parent )
							) {
								$test_array = array(
									'menu-item-title'     => $page_to_add->post_title,
									'menu-item-parent-id' => $new_menu_obj[ $page_to_add->post_parent ]['menu-item'],
									'post-parent'         => $page_to_add->post_parent,
									'menu-item-object-id' => $page_to_add->ID,
								);
							}

							$valid_parent_ids[] = $page_to_add->ID;
							unset( $pages_to_add[ $index ] );
						} else {
							$skipped_pages++;
						}
					}
				} while ( 0 < $skipped_pages );
			}
		}
	}
}
add_action( 'wp', 'yoko_child_theme_create_menu_from_page_structure' );