/* tags are passed as a comma and/or space seperated string
   * for exmaple:
   * "Documentation Database, Other"  <=- this is 3 tags
   */
  public function setTags($tags)
  {
    $orig_tags = $this->getTags();

    $new = explode(',', $tags);
    $old = explode(',', $orig_tags);

    $new = array_map('trim', $new);
    $old = array_map('trim', $old);

    $added = array_diff($new, $old);
    $removed = array_diff($old, $new);

    $message = 'New Tags: ';
    foreach($added as $n)
    {
       $message .= '"'.$n.'","';
    }
    sfContext::getInstance()->getLogger()->log($message);

    $message = 'Tags to remove: ';
    foreach($removed as $n)
    {
       $message .= '"'.$n.'",';
    }
    sfContext::getInstance()->getLogger()->log($message);


    // remove the old ones!
    foreach($removed as $name)
    {
      foreach($this->Tag as $k => $t)
      {
        if ($t->name == $name)
        {
          $this->unlink('Tag', array($t->id));
        }
      }
    }


    // uses LIKE for case-insensitivity
    $find_q = new Doctrine_Query();
    $find_q->select('t.id')
           ->from('Tag t')
           ->where('t.name LIKE ?');

    foreach($added as $name)
    {
      // first, lets see if a tag by this name already exists
      $ret = $find_q->fetchOne(array($name));
      if (!$ret)
      {
        $ret = new Tag();
        $ret->name = $name;
      }
      $this->Tag[] = $ret;
    }

  }