class Twig_NodeVisitor_Sandbox

class Twig_NodeVisitor_Sandbox implements Twig_NodeVisitorInterface {
  protected $inAModule = false;
  protected $tags;
  protected $filters;
  protected $functions;

  /**
   * Called before child nodes are visited.
   *
   * @param Twig_NodeInterface $node The node to visit
   * @param Twig_Environment   $env  The Twig environment instance
   *
   * @return Twig_NodeInterface The modified node
   */
  public function enterNode(Twig_NodeInterface $node, Twig_Environment $env) {
    if ($node instanceof Twig_Node_Module) {
      $this->inAModule = true;
      $this->tags = array();
      $this->filters = array();
      $this->functions = array();
      return $node;
    }
    elseif ($this->inAModule) {

      // look for tags
      if ($node
        ->getNodeTag()) {
        $this->tags[] = $node
          ->getNodeTag();
      }

      // look for filters
      if ($node instanceof Twig_Node_Expression_Filter) {
        $this->filters[] = $node
          ->getNode('filter')
          ->getAttribute('value');
      }

      // look for functions
      if ($node instanceof Twig_Node_Expression_Function) {
        $this->functions[] = $node
          ->getAttribute('name');
      }

      // wrap print to check __toString() calls
      if ($node instanceof Twig_Node_Print) {
        return new Twig_Node_SandboxedPrint($node
          ->getNode('expr'), $node
          ->getLine(), $node
          ->getNodeTag());
      }
    }
    return $node;
  }

  /**
   * Called after child nodes are visited.
   *
   * @param Twig_NodeInterface $node The node to visit
   * @param Twig_Environment   $env  The Twig environment instance
   *
   * @return Twig_NodeInterface The modified node
   */
  public function leaveNode(Twig_NodeInterface $node, Twig_Environment $env) {
    if ($node instanceof Twig_Node_Module) {
      $this->inAModule = false;
      return new Twig_Node_SandboxedModule($node, array_unique($this->filters), array_unique($this->tags), array_unique($this->functions));
    }
    return $node;
  }

  /**
   * {@inheritdoc}
   */
  public function getPriority() {
    return 0;
  }

}