WordPress submenu tree generator from a list of menu items 🤯

wp_menu_tree.php

// usage `get_menu_tree('your_menu');`
// PHP 5,7 and 8

function get_menu($menu_name) {
  if (( $locations = get_nav_menu_locations()) && isset( $locations[$menu_name])) {
    return wp_get_nav_menu_items($locations[$menu_name]);
  }

  return null;
}

function build_tree_from_index($level, $index, $carry = null) {
  foreach( $level as $key => $value ) {
    if (!empty($carry) && $carry['parent_id'] === $key) {
      $level->offsetSet($key, $carry->getArrayCopy());
      $carry = null;
    }

    if ($index->offsetExists($value['parent_id'])) {
      if ($index->offsetExists($key)) $index->offsetUnset($key);
      $carry = $value->getArrayCopy();
    }

    if ($value['sub_items']->count()) {
      build_tree_from_index($value['sub_items'], $index, $carry);
    } else {
      if ($index->offsetExists($value['id']) && !empty($value['parent_id'])) {
        $index->offsetUnset($value['id']);
      }
    }
  }
}

function index_menu_items($menu, $menu_index) {
  foreach( $menu as $menu_item ) {
    $parent_id = $menu_item->menu_item_parent;
    $has_parent = !empty($parent_id);
    $id = $menu_item->object_id;

    $value = new ArrayObject(array(
      'id' => $id,
      'title' => $menu_item->title,
      'url' => $menu_item->url,
      'parent_id' => $parent_id,
      'sub_items' => new ArrayObject(array())
    ));

    if ($has_parent) {
      if ($menu_index->offsetExists($parent_id)) {
        $menu_index[$parent_id]['sub_items']->offsetSet($id, $value);
      }
    }

    $menu_index->offsetSet($id, $value);
  }
}

function get_menu_tree($menu_name) {
  $menu = get_menu($menu_name);
  $menu_index = new ArrayObject(array());

  index_menu_items($menu, $menu_index);
  build_tree_from_index($menu_index, $menu_index);

  return $menu_index;
}