Custom wordpress menu: Get menu as hierarchical array with children

Menu.php

<?php

/*
 * Helper class to display menu items in a hierarchical array
 * Usage: $mainMenu = new Menu('primary'); 
 *        $menuItems = $mainMenu->getTree();
 *        $menuItems = $mainMenu->getMenuItems();
*/ 


class Menu {

	protected $menu;
	protected $tree;

	/**
	 * Initialises $this->menu
	 */

	public function __construct($menuName = '', $args = array(), $filter = null) {
		
		$filter = is_callable($filter) ? $filter : null;

		if (empty($menuName)) {
			throw new Exception('No menu location name provided.');
			return;
		}

		$menuLocations = get_nav_menu_locations();
		if (empty($menuLocations[$menuName])) return;
	
		$this->menu = $this->retrieveMenu(wp_get_nav_menu_object($menuLocations[$menuName]), $args, $filter);
	}


	/**
	 * Retrieves menu from wordpress
	 * @uses  private core function _wp_menu_item_classes_by_context()
	 * @return Array|null $this->menu 
	 */

	protected function retrieveMenu($navMenuObject = null, $args = array(), $filter = null) {

		global $wp_query;
		global $post;

		$queriedPostType = get_post_type();
		$this->queriedPostType = $queriedPostType;

		$isTax = (is_tax() || is_tag());

		if (!$navMenuObject) return null;
		
		$menu_items = wp_get_nav_menu_items( $navMenuObject->term_id , $args );

	    /* the following was taken from wp_nav_menu core function 
		 * line 154–169: https://developer.wordpress.org/reference/functions/wp_nav_menu/
	     */

	    // set up menu item classes
	    _wp_menu_item_classes_by_context($menu_items);

	    $sorted_menu_items = $menu_items_with_children = array();
	    foreach ( (array) $menu_items as $menu_item ) {
	        $sorted_menu_items[ $menu_item->menu_order ] = $menu_item;
	        if ( $menu_item->menu_item_parent )
	            $menu_items_with_children[ $menu_item->menu_item_parent ] = true;
	    }
	 
	    // Add the menu-item-has-children class where applicable
	    if ( $menu_items_with_children ) {
	        foreach ( $sorted_menu_items as &$menu_item ) {
	            if ( isset( $menu_items_with_children[ $menu_item->ID ] ) )
	                $menu_item->classes[] = 'menu-item-has-children';
	        }
	    }
	    /* 
	     * end taken wp_nav_menu from core function 
	     */

		foreach($menu_items as $key => &$menu_item) {

			// Add isCurrent class to parents or ancestors
			$menu_item->isCurrent = false;

	    	if ($menu_item->current_item_ancestor) $menu_item->isCurrent = 'ancestor';

	    	if ($menu_item->current_item_parent && ($menu_item->type !== 'taxonomy')) {
	    		$menu_item->isCurrent = 'parent ancestor';
	    	}

	    	if ($menu_item->current) $menu_item->isCurrent = 'current';

	    	// Add isCurrent class, and ancestor classes to custom post type archive menu items
    		$isCurrentCustomPostType = static::menuItemIsCustomPostTypeArchive($menu_item, $queriedPostType);

    		// if is current
    		if ($isCurrentCustomPostType) {
    			$menu_item->classes[] = "current-{$queriedPostType}-ancestor";
    			$menu_item->isCurrent = 'ancestor';
    		}

    		// if is current and !hierarchical
    		if ($isCurrentCustomPostType && !is_post_type_hierarchical($queriedPostType)) {
    			$menu_item->classes[] = "current-{$queriedPostType}-parent";
    			$menu_item->isCurrent = 'parent ancestor';
    		}

    		// if is current and hierarchical and top level
    		if ($post 
    			&& $isCurrentCustomPostType 
    			&& is_post_type_hierarchical($queriedPostType) 
    			&& (count(get_post_ancestors($post->ID)) === 0)
    			) {
    				$menu_item->classes[] = "current-{$queriedPostType}-parent";
    				$menu_item->isCurrent = 'parent ancestor';
    		}

	    	// if a filter exists, run it
    		if ($filter && is_callable($filter)) {
    			$filtered = $filter($menu_item);
    			$menu_item = $filtered ? $filtered : null;
    			if (!$menu_item) unset($menu_items[$key]);
    		}
	   	 }
	    
		return $this->menu = $menu_items;
	}


	/**
	 * Returns $this->menu
	 */

	public function getMenuItems() {
		return $this->menu;
	}


	/**
	 * Returns $this->tree
	 *
	 * @return Array|null $tree 
	 */

	public function getTree() {
		if ($this->tree !== null) return $this->tree;
		$tree = static::buildTree($this->menu, 0, 1);
	    return $tree ? $tree : null;
	}


	/**
	 * Transform a navigational menu to a tree structure
	 *
	 * @return Array $branch 
	 */

	public static function buildTree(array &$elements, $parentId = 0, $level = 1) {

	    $branch = array();
	    foreach ( $elements as &$element ) {

	        if ( $element->menu_item_parent == $parentId ) {

	        	$subLevel = $level + 1;

	        	$element->level = $level;

	            $children = static::buildTree( $elements, $element->ID, $subLevel );
	            
	            if ($children) {
	                $element->children = $children;
	            } else {
	            	$element->children = array();
	            }

	            $branch[$element->ID] = $element;
	            unset($element);
	        }
	    }
	    return $branch;
	}


	/**
	 * Checks if menu item is a custom post type archive
	 *
	 * @return Boolean
	 */

	protected static function menuItemIsCustomPostTypeArchive($menuItem, $type = null) {

		$isCustomPostType = (
			isset($menuItem->type) 
			&& ($menuItem->type === 'post_type_archive')
			&& (is_post_type_archive($this->queriedPostType) || is_singular($this->queriedPostType))
		);

		if (!$type) {
			return $isCustomPostType;
		}

		$isOfType = (
			$isCustomPostType
			&& isset($menuItem->object)
			&& ($menuItem->object === $type)
		);
		
		return $isOfType;
	}


	/**
	 * Returns maximum depth of menu tree
	 *
	 * @return Integer
	 */

	public static function menuItemDepth($menuItem = null) {
	    $maxDepth = 0;
	    foreach ($menuItem->children as $child) {
	        if (is_array($child->children)) {
	            $depth = static::menuItemDepth($child) + 1;
	            if ($depth > $maxDepth) $maxDepth = $depth;
	        }
	    }
	    return $maxDepth;
	}
}