php sorting head builder class by num

<?php
/**
* Sorting Head Builder For Dynamic Table
*
* @author  Num
* @link  http://web-programming-bookmark.blogspot.com
*/
class SortHead
{
 protected $ccol = '';
 protected $cdir = '';
 protected $ncol = '';
 protected $ndir = '';
 protected $dfcol = '';
 protected $dfdir = '';
 protected $cols = array();
 public $col = '';
 public $dir = '';
 public function __construct(array $cols,$cname,$dname,$dfcol,$dfdir){
  $this->cols = $cols;
  $this->dfcol = $dfcol;
  $this->dfdir = $dfdir;
  $this->ncol = $cname;
  $this->ndir = $dname;
  $this->ccol = $this->current_col();
  $this->cdir = $this->current_dir($this->ccol,$dfdir);
  $this->col = $this->ccol;
  $this->dir = $this->cdir;
 }
 public function current_col(){
  $ccol = empty($_GET[$this->ncol]) ? $this->dfcol : $_GET[$this->ncol];
  $k = array_search($ccol,$this->cols,true);
  return ($k === false) ?$this->dfcol :$this->cols[$k];
 }
 public function current_dir($col,$dfdir='desc'){
  $odir = $dfdir == 'desc' ?'asc' :'desc';
  if ($this->ccol == $col){
   $dir = empty($_GET[$this->ndir]) ?$dfdir :$_GET[$this->ndir];
   if ($dir != 'asc' && $dir != 'desc') $dir = 'desc';
   $dir = $dir == 'desc' ?'desc' :'asc';
  }else{
   $dir = $dfdir;
  }
  return $dir;
 }
 public function next_dir($col,$dfdir='desc'){
  $odir = $dfdir == 'desc' ?'asc' :'desc';
  if ($this->ccol == $col){
   $dir = empty($_GET[$this->ndir]) ?$dfdir :$_GET[$this->ndir];
   if ($dir != 'asc' && $dir != 'desc') $dir = 'desc';
   $dir = $dir == 'desc' ?'asc' :'desc';
  }else{
   $dir = $dfdir;
  }
  return $dir;
 }
 public function link($col,$dfdir='desc'){
  $dir = $this->next_dir($col,$dfdir);
  return '?'.$this->ncol.'='.$col.'&'.$this->ndir.'='.$dir;
 }
 public function dir($col,$dfdir='desc'){
  return $this->current_dir($col,$dfdir);
 }
}

$sh = new SortHead(array('name','title','id'),'st','sd','id','desc');

//safe for query
echo ', field=',$sh->col;
echo ', dir=',$sh->dir;
echo ', select * from tb order by '.$sh->col.' '.$sh->dir;

?>

<table border="1" cellpadding="10" cellspacing="0">
<tr>
<td>
<a href="<?php echo $sh->link('name','asc') ?>">name <?php echo $sh->dir('name','asc') ?></a>

</td>
<td>
<a href="<?php echo $sh->link('title') ?>">title <?php echo $sh->dir('title') ?></a>
</td>
<td>
<a href="<?php echo $sh->link('id') ?>">id <?php echo $sh->dir('id') ?></a>

</td>
</tr>
</table>