Utility classes

/**
 * Unfinished, not used in any solution
 */

#[AllowDynamicProperties]
class Tree
{
    /**
     * Create a new tree
     *
     * @param array $relations Relations of [parent=>children]
     */
    public function __construct($relations)
    {
        $this->nodes = set();

        foreach ($relations as $parent=>$children) {
            $node = $this->add($parent);
            foreach ($children as $child) $node->addChild($node);
        }
    }

    /**
     * Add a unique node
     *
     * @param string $id
     * @return TreeNode
     */
    public function add($id)
    {
        return $this->get($id) ?: $this->nodes[$id] = new TreeNode($id, $this);
    }

    /**
     * Get a specific node
     *
     * @param string $id
     * @return TreeNode|null
     */
    public function get($id)
    {
        return $this->nodes[$id] ?? null;
    }


}

#[AllowDynamicProperties]
class TreeNode
{
    public function __construct(public $id, private $tree)
    {
        $this->parent = false;
        $this->children = set([]);
    }

    /**
     * Add a new child by id
     *
     * @return void
     */
    public function addChild($id)
    {
        if (isset($this->children[$id])) return $this->children[$id];
        $child = $this->tree->add($id);
        $child->setParent($this->id);
        $this->children[$id] = $child;
        return $child;
    }

    /**
     * Set the parent of a node
     *
     * @param string $parent_id The parent node ID
     * @return self
     */
    public function setParent($parent_id)
    {
        $this->parent = $this->tree->add($parent_id);
        return $this;
    }
}