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) return $this->tree;
		return static::buildTree($this->menu, 0, 1);
	}


	/**
	 * 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(get_post_type()) || is_singular(get_post_type()))
		);

		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;
	}
}

@MichaelAnd you should add a backlink and author tag as well, as there are projects simply including the file as is (like wuxt for example, you get attributed in the readme, but when just looking at the file it is not clear)