<?php
namespace HTML5\Serializer;

/**
 * Traverser for walking a DOM tree.
 *
 * This is a concrete traverser designed to convert a DOM tree into an 
 * HTML5 document. It is not intended to be a generic DOMTreeWalker 
 * implementation.
 *
 * @see http://www.w3.org/TR/2012/CR-html5-20121217/syntax.html#serializing-html-fragments
 */
class Traverser {

  /** Namespaces that should be treated as "local" to HTML5. */
  static $local_ns = array(
    'http://www.w3.org/1999/xhtml' => 'html',
    'http://www.w3.org/1998/Math/MathML' => 'math',
    'http://www.w3.org/2000/svg' => 'svg',
  );

  protected $dom;
  protected $options;
  protected $encode = FALSE;
  protected $rules;
  protected $out;

  /**
   * Create a traverser.
   *
   * @param DOMNode|DOMNodeList $dom
   *   The document or node to traverse.
   * @param resource $out
   *   A stream that allows writing. The traverser will output into this 
   *   stream.
   * @param array $options
   *   An array or options for the traverser as key/value pairs. These include:
   *   - encode_entities: A bool to specify if full encding should happen for all named
   *     charachter references. Defaults to FALSE which escapes &'<>".
   *   - output_rules: The path to the class handling the output rules.
   */
  public function __construct($dom, $out, RulesInterface $rules, $options = array()) {
    $this->dom = $dom;
    $this->out = $out;
    $this->rules = $rules;
    $this->options = $options;

    $this->rules->setTraverser($this);
  }

  /**
   * Tell the traverser to walk the DOM.
   *
   * @return resource $out
   *   Returns the output stream.
   */
  public function walk() {
    
    if ($this->dom instanceof \DOMDocument) {
      $this->rules->document($this->dom);
    }
    elseif ($this->dom instanceof \DOMDocumentFragment) {
      // Document fragments are a special case. Only the children need to
      // be serialized.
      if ($this->dom->hasChildNodes()) {
        $this->children($this->dom->childNodes);
      }
    }
    // If NodeList, loop
    elseif ($this->dom instanceof \DOMNodeList) {
      // If this is a NodeList of DOMDocuments this will not work.
      $this->children($this->dom);
    }
    // Else assume this is a DOMNode-like datastructure.
    else {
      $this->node($this->dom);
    }

    return $this->out;
  }

  /**
   * Process a node in the DOM.
   *
   * @param mixed $node
   *   A node implementing \DOMNode.
   */
  public function node($node) {
    // A listing of types is at http://php.net/manual/en/dom.constants.php
    switch ($node->nodeType) {
      case XML_ELEMENT_NODE:
        $this->rules->element($node);
        break;
      case XML_TEXT_NODE:
        $this->rules->text($node);
        break;
      case XML_CDATA_SECTION_NODE:
        $this->rules->cdata($node);
        break;
      // FIXME: It appears that the parser doesn't do PI's.
      case XML_PI_NODE:
        $this->rules->processorInstruction($node);
        break;
      case XML_COMMENT_NODE:
        $this->rules->comment($node);
        break;
      // Currently we don't support embedding DTDs.
      default:
        print '<!-- Skipped -->';
        break;
    }
  }

  /**
   * Walk through all the nodes on a node list.
   *
   * @param \DOMNodeList $nl
   *   A list of child elements to walk through.
   */
  public function children($nl) {
    foreach ($nl as $node) {
      $this->node($node);
    }
  }

  /**
   * Is an element local?
   *
   * @param mixed $ele
   *   An element that implement \DOMNode.
   *
   * @return bool
   *   True if local and false otherwise.
   */
  public function isLocalElement($ele) {
    $uri = $ele->namespaceURI;
    if (empty($uri)) {
      return FALSE;
    }
    return isset(static::$local_ns[$uri]);
  }
}