class Twig_NodeVisitor_SafeAnalysis

class Twig_NodeVisitor_SafeAnalysis implements Twig_NodeVisitorInterface {
  protected $data = array();
  public function getSafe(Twig_NodeInterface $node) {
    $hash = spl_object_hash($node);
    if (isset($this->data[$hash])) {
      foreach ($this->data[$hash] as $bucket) {
        if ($bucket['key'] === $node) {
          return $bucket['value'];
        }
      }
    }
    return null;
  }
  protected function setSafe(Twig_NodeInterface $node, array $safe) {
    $hash = spl_object_hash($node);
    if (isset($this->data[$hash])) {
      foreach ($this->data[$hash] as &$bucket) {
        if ($bucket['key'] === $node) {
          $bucket['value'] = $safe;
          return;
        }
      }
    }
    $this->data[$hash][] = array(
      'key' => $node,
      'value' => $safe,
    );
  }
  public function enterNode(Twig_NodeInterface $node, Twig_Environment $env) {
    return $node;
  }
  public function leaveNode(Twig_NodeInterface $node, Twig_Environment $env) {
    if ($node instanceof Twig_Node_Expression_Constant) {

      // constants are marked safe for all
      $this
        ->setSafe($node, array(
        'all',
      ));
    }
    elseif ($node instanceof Twig_Node_Expression_BlockReference) {

      // blocks are safe by definition
      $this
        ->setSafe($node, array(
        'all',
      ));
    }
    elseif ($node instanceof Twig_Node_Expression_Parent) {

      // parent block is safe by definition
      $this
        ->setSafe($node, array(
        'all',
      ));
    }
    elseif ($node instanceof Twig_Node_Expression_Conditional) {

      // intersect safeness of both operands
      $safe = $this
        ->intersectSafe($this
        ->getSafe($node
        ->getNode('expr2')), $this
        ->getSafe($node
        ->getNode('expr3')));
      $this
        ->setSafe($node, $safe);
    }
    elseif ($node instanceof Twig_Node_Expression_Filter) {

      // filter expression is safe when the filter is safe
      $name = $node
        ->getNode('filter')
        ->getAttribute('value');
      $args = $node
        ->getNode('arguments');
      if (false !== ($filter = $env
        ->getFilter($name))) {
        $safe = $filter
          ->getSafe($args);
        if (null === $safe) {
          $safe = $this
            ->intersectSafe($this
            ->getSafe($node
            ->getNode('node')), $filter
            ->getPreservesSafety());
        }
        $this
          ->setSafe($node, $safe);
      }
      else {
        $this
          ->setSafe($node, array());
      }
    }
    elseif ($node instanceof Twig_Node_Expression_Function) {

      // function expression is safe when the function is safe
      $name = $node
        ->getAttribute('name');
      $args = $node
        ->getNode('arguments');
      $function = $env
        ->getFunction($name);
      if (false !== $function) {
        $this
          ->setSafe($node, $function
          ->getSafe($args));
      }
      else {
        $this
          ->setSafe($node, array());
      }
    }
    elseif ($node instanceof Twig_Node_Expression_MethodCall) {
      if ($node
        ->getAttribute('safe')) {
        $this
          ->setSafe($node, array(
          'all',
        ));
      }
      else {
        $this
          ->setSafe($node, array());
      }
    }
    else {
      $this
        ->setSafe($node, array());
    }
    return $node;
  }
  protected function intersectSafe(array $a = null, array $b = null) {
    if (null === $a || null === $b) {
      return array();
    }
    if (in_array('all', $a)) {
      return $b;
    }
    if (in_array('all', $b)) {
      return $a;
    }
    return array_intersect($a, $b);
  }

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

}