<?php declare(strict_types = 1);

namespace PHPStan\PhpDocParser\Ast;

/**
 * Inspired by https://github.com/nikic/PHP-Parser/tree/36a6dcd04e7b0285e8f0868f44bd4927802f7df1
 *
 * Copyright (c) 2011, Nikita Popov
 * All rights reserved.
 */
interface NodeVisitor
{

	/**
	 * Called once before traversal.
	 *
	 * Return value semantics:
	 *  * null:      $nodes stays as-is
	 *  * otherwise: $nodes is set to the return value
	 *
	 * @param Node[] $nodes Array of nodes
	 *
	 * @return Node[]|null Array of nodes
	 */
	public function beforeTraverse(array $nodes): ?array;

	/**
	 * Called when entering a node.
	 *
	 * Return value semantics:
	 *  * null
	 *        => $node stays as-is
	 *  * array (of Nodes)
	 *        => The return value is merged into the parent array (at the position of the $node)
	 *  * NodeTraverser::REMOVE_NODE
	 *        => $node is removed from the parent array
	 *  * NodeTraverser::DONT_TRAVERSE_CHILDREN
	 *        => Children of $node are not traversed. $node stays as-is
	 *  * NodeTraverser::DONT_TRAVERSE_CURRENT_AND_CHILDREN
	 *        => Further visitors for the current node are skipped, and its children are not
	 *           traversed. $node stays as-is.
	 *  * NodeTraverser::STOP_TRAVERSAL
	 *        => Traversal is aborted. $node stays as-is
	 *  * otherwise
	 *        => $node is set to the return value
	 *
	 * @param Node $node Node
	 *
	 * @return Node|Node[]|NodeTraverser::*|null Replacement node (or special return value)
	 */
	public function enterNode(Node $node);

	/**
	 * Called when leaving a node.
	 *
	 * Return value semantics:
	 *  * null
	 *        => $node stays as-is
	 *  * NodeTraverser::REMOVE_NODE
	 *        => $node is removed from the parent array
	 *  * NodeTraverser::STOP_TRAVERSAL
	 *        => Traversal is aborted. $node stays as-is
	 *  * array (of Nodes)
	 *        => The return value is merged into the parent array (at the position of the $node)
	 *  * otherwise
	 *        => $node is set to the return value
	 *
	 * @param Node $node Node
	 *
	 * @return Node|Node[]|NodeTraverser::REMOVE_NODE|NodeTraverser::STOP_TRAVERSAL|null Replacement node (or special return value)
	 */
	public function leaveNode(Node $node);

	/**
	 * Called once after traversal.
	 *
	 * Return value semantics:
	 *  * null:      $nodes stays as-is
	 *  * otherwise: $nodes is set to the return value
	 *
	 * @param Node[] $nodes Array of nodes
	 *
	 * @return Node[]|null Array of nodes
	 */
	public function afterTraverse(array $nodes): ?array;

}