<?php

declare(strict_types=1);

namespace App\Util;

/**
 * Represents a node in a tree.
 *
 * @author Adam Pippin <hello@adampippin.ca>
 */
class GraphNode
{
	/**
	 * Parent of this node.
	 * @var GraphNode
	 */
	protected $parent;

	/**
	 * Value of this node.
	 * @var mixed
	 */
	protected $value;

	/**
	 * Children of this node.
	 * @var GraphNode[]
	 */
	protected $children;

	/**
	 * Create a new graph node.
	 *
	 * @param mixed $value
	 */
	public function __construct($value = null)
	{
		$this->value = $value;
		$this->children = [];
	}

	/**
	 * Set the value of this node.
	 *
	 * @param  mixed $value
	 * @return void
	 */
	public function setValue($value): void
	{
		$this->value = $value;
	}

	/**
	 * Get the value of this node.
	 *
	 * @return mixed
	 */
	public function getValue()
	{
		return $this->value;
	}

	/**
	 * Set the parent node of this node.
	 *
	 * @param  GraphNode $node
	 * @return void
	 */
	public function setParent(GraphNode $node): void
	{
		$this->parent = $node;
	}

	/**
	 * Determine whether this node has a parent.
	 *
	 * @return bool
	 */
	public function hasParent(): bool
	{
		return isset($this->parent);
	}

	/**
	 * Get this node's parent node.
	 *
	 * @return GraphNode
	 */
	public function getParent(): GraphNode
	{
		return $this->parent;
	}

	/**
	 * Count how many child nodes this node has.
	 *
	 * @return int
	 */
	public function countChildren(): int
	{
		return sizeof($this->children);
	}

	/**
	 * Determine whether this node has any children.
	 *
	 * @return bool
	 */
	public function hasChildren(): bool
	{
		return sizeof($this->children) > 0;
	}

	/**
	 * Fetch all of this node's children.
	 *
	 * @return GraphNode[]
	 */
	public function getChildren(): array
	{
		return $this->children;
	}

	/**
	 * Add a node to this child's list of children.
	 *
	 * @param  GraphNode $child
	 * @return void
	 */
	public function appendChild(GraphNode $child): void
	{
		$this->children[] = $child;
		$child->setParent($this);
	}

	/**
	 * Replace a child node with another node.
	 *
	 * @param  GraphNode $original
	 * @param  GraphNode $new
	 * @return void
	 */
	public function replaceChild(GraphNode $original, GraphNode $new): void
	{
		for ($i = 0; $i < sizeof($this->children); $i++)
		{
			if ($this->children[$i] === $original)
			{
				$this->children[$i] = $new;
				$new->setParent($this);
				return;
			}
		}
	}

	/**
	 * Remove all children of this node.
	 *
	 * @return void
	 */
	public function clearChildren(): void
	{
		$this->children = [];
	}

	/**
	 * Add a child node by value.
	 *
	 * @param  mixed     $value value to add as a child
	 * @return GraphNode the node created as a child
	 */
	public function add($value): GraphNode
	{
		$this->children[] = new GraphNode($value);
		end($this->children)->setParent($this);
		return end($this->children);
	}

	/**
	 * Walk through this node and all children, calling callback on each node.
	 *
	 * Callback is called on a node's children before a node
	 *
	 * @param  callable $callback callback(GraphNode $node): void
	 * @return void
	 */
	public function walk(callable $callback)
	{
		static::walkNodes([$this], $callback);
	}

	/**
	 * Internal function for recursively visiting all nodes.
	 *
	 * @param  GraphNode[] $nodes
	 * @param  callable    $callback
	 * @return void
	 */
	protected static function walkNodes(array $nodes, callable $callback)
	{
		foreach ($nodes as $node)
		{
			if ($node->hasChildren())
			{
				static::walkNodes($node->getChildren(), $callback);
			}

			$callback($node);
		}
	}
}