<?php
  namespace Dompdf\Frame;
  
  use Iterator;
  use Dompdf\Frame;
  
  /**
   * Pre-order Iterator
   *
   * Returns frames in preorder traversal order (parent then children)
   *
   * @access private
   * @package dompdf
   */
  class FrameTreeIterator implements Iterator
  {
      /**
       * @var Frame
       */
      protected $_root;
  
      /**
       * @var array
       */
      protected $_stack = array();
  
      /**
       * @var int
       */
      protected $_num;
  
      /**
       * @param Frame $root
       */
      public function __construct(Frame $root)
      {
          $this->_stack[] = $this->_root = $root;
          $this->_num = 0;
      }
  
      /**
       *
       */
      public function rewind()
      {
          $this->_stack = array($this->_root);
          $this->_num = 0;
      }
  
      /**
       * @return bool
       */
      public function valid()
      {
          return count($this->_stack) > 0;
      }
  
      /**
       * @return int
       */
      public function key()
      {
          return $this->_num;
      }
  
      /**
       * @return Frame
       */
      public function current()
      {
          return end($this->_stack);
      }
  
      /**
       * @return Frame
       */
      public function next()
      {
          $b = end($this->_stack);
  
          // Pop last element
          unset($this->_stack[key($this->_stack)]);
          $this->_num++;
  
          // Push all children onto the stack in reverse order
          if ($c = $b->get_last_child()) {
              $this->_stack[] = $c;
              while ($c = $c->get_prev_sibling()) {
                  $this->_stack[] = $c;
              }
          }
  
          return $b;
      }
  }