interface MenuLinkTreeInterface

interface MenuLinkTreeInterface {
    
    /**
     * Gets the link tree parameters for rendering a specific menu.
     *
     * Builds menu link tree parameters that:
     * - Expand all links in the active trail based on route being viewed.
     * - Expand the descendants of the links in the active trail whose
     *   'expanded' flag is enabled.
     *
     * This only sets the (relatively complex) parameters to achieve the two above
     * goals, but you can still further customize these parameters.
     *
     * @param string $menu_name
     *   The menu name, needed for retrieving the active trail and links with the
     *   'expanded' flag enabled.
     *
     * @return \Drupal\Core\Menu\MenuTreeParameters
     *   The parameters to determine which menu links to be loaded into a tree.
     *
     * @see \Drupal\Core\Menu\MenuTreeParameters
     */
    public function getCurrentRouteMenuTreeParameters($menu_name);
    
    /**
     * Loads a menu tree with a menu link plugin instance at each element.
     *
     * @param string $menu_name
     *   The name of the menu.
     * @param \Drupal\Core\Menu\MenuTreeParameters $parameters
     *   The parameters to determine which menu links to be loaded into a tree.
     *
     * @return \Drupal\Core\Menu\MenuLinkTreeElement[]
     *   A menu link tree.
     */
    public function load($menu_name, MenuTreeParameters $parameters);
    
    /**
     * Applies menu link tree manipulators to transform the given tree.
     *
     * @param \Drupal\Core\Menu\MenuLinkTreeElement[] $tree
     *   The menu tree to manipulate.
     * @param array $manipulators
     *   The menu link tree manipulators to apply. Each is an array with keys:
     *   - callable: a callable or a string that can be resolved to a callable
     *     by \Drupal\Core\Controller\ControllerResolverInterface::getControllerFromDefinition()
     *   - args: optional array of arguments to pass to the callable after $tree.
     *
     * @return \Drupal\Core\Menu\MenuLinkTreeElement[]
     *   The manipulated menu link tree.
     */
    public function transform(array $tree, array $manipulators);
    
    /**
     * Builds a renderable array from a menu tree.
     *
     * The menu item's LI element is given one of the following classes:
     * - expanded: The menu item is showing its submenu.
     * - collapsed: The menu item has a submenu that is not shown.
     * - leaf: The menu item has no submenu.
     *
     * @param \Drupal\Core\Menu\MenuLinkTreeElement[] $tree
     *   A data structure representing the tree, as returned from
     *   MenuLinkTreeInterface::load().
     *
     * @return array
     *   A renderable array.
     */
    public function build(array $tree);
    
    /**
     * Returns the maximum depth of tree that is supported.
     *
     * @return int
     *   The maximum depth.
     */
    public function maxDepth();
    
    /**
     * Finds the height of a subtree rooted by of the given ID.
     *
     * @param string $id
     *   The ID of an item in the storage.
     *
     * @return int
     *   Returns the height of the subtree. This will be at least 1 if the ID
     *   exists, or 0 if the ID does not exist in the storage.
     */
    public function getSubtreeHeight($id);
    
    /**
     * Finds expanded links in a menu given a set of possible parents.
     *
     * @param string $menu_name
     *   The menu name.
     * @param array $parents
     *   One or more parent IDs to match.
     *
     * @return array
     *   The menu link IDs that are flagged as expanded in this menu.
     */
    public function getExpanded($menu_name, array $parents);

}