<?php

/*
 * This file is part of Twig.
 *
 * (c) Fabien Potencier
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

/**
 * Twig_BaseNodeVisitor can be used to make node visitors compatible with Twig 1.x and 2.x.
 *
 * @author Fabien Potencier <fabien@symfony.com>
 */
abstract class Twig_BaseNodeVisitor implements Twig_NodeVisitorInterface
{
  /**
   * {@inheritdoc}
   */
  final public function enterNode(Twig_NodeInterface $node, Twig_Environment $env)
  {
    if (!$node instanceof Twig_Node) {
      throw new LogicException('Twig_BaseNodeVisitor only supports Twig_Node instances.');
    }

    return $this->doEnterNode($node, $env);
  }

  /**
   * {@inheritdoc}
   */
  final public function leaveNode(Twig_NodeInterface $node, Twig_Environment $env)
  {
    if (!$node instanceof Twig_Node) {
      throw new LogicException('Twig_BaseNodeVisitor only supports Twig_Node instances.');
    }

    return $this->doLeaveNode($node, $env);
  }

  /**
   * Called before child nodes are visited.
   *
   * @param Twig_Node        $node The node to visit
   * @param Twig_Environment $env  The Twig environment instance
   *
   * @return Twig_Node The modified node
   */
  abstract protected function doEnterNode(Twig_Node $node, Twig_Environment $env);

  /**
   * Called after child nodes are visited.
   *
   * @param Twig_Node        $node The node to visit
   * @param Twig_Environment $env  The Twig environment instance
   *
   * @return Twig_Node|false The modified node or false if the node must be removed
   */
  abstract protected function doLeaveNode(Twig_Node $node, Twig_Environment $env);
}
