wp-bootstrap/inc/Template/NavWalker.php

<?php
/**
 * Bootstrap 5 Navigation Walker.
 *
 * Converts flat WordPress menu items into a nested tree
 * suitable for rendering Bootstrap navbar dropdowns in Twig.
 *
 * @package WPBootstrap
 * @since 0.1.1
 */

namespace WPBootstrap\Template;

class NavWalker
{
    /**
     * Build a nested menu tree from flat WordPress menu items.
     *
     * @param array $items Array of WP_Post menu item objects.
     * @return array Nested array suitable for Twig iteration.
     */
    public function buildTree(array $items): array
    {
        $tree    = [];
        $children = [];

        foreach ($items as $item) {
            $node = [
                'id'       => (int) $item->ID,
                'title'    => $item->title,
                'url'      => $item->url,
                'target'   => $item->target ?: '',
                'classes'  => implode(' ', array_filter($item->classes ?? [])),
                'active'   => $this->isActive($item),
                'children' => [],
            ];

            if ((int) $item->menu_item_parent === 0) {
                $tree[$item->ID] = $node;
            } else {
                $children[(int) $item->menu_item_parent][] = $node;
            }
        }

        // Assign children to their parent items.
        foreach ($children as $parentId => $childItems) {
            if (isset($tree[$parentId])) {
                $tree[$parentId]['children'] = $childItems;
            }
        }

        return array_values($tree);
    }

    /**
     * Determine if a menu item is currently active.
     */
    private function isActive(object $item): bool
    {
        $classes = $item->classes ?? [];

        if (in_array('current-menu-item', $classes, true)) {
            return true;
        }

        if (in_array('current-menu-ancestor', $classes, true)) {
            return true;
        }

        if ($item->object === 'page' && is_page((int) $item->object_id)) {
            return true;
        }

        if ($item->object === 'category' && is_category((int) $item->object_id)) {
            return true;
        }

        return false;
    }
}