Clear user session

<?php
$id = $modx->resource->id;

if (!isset($limit)) {$limit = 12;}
if (!isset($show)) {$show = 0;}
if (!isset($snippet)) {$snippet = 0;}
if (!isset($parents)) {$parents = 0;}
if (!isset($thumbs)) {$thumbs = '300x300';}
if (!isset($tpl)) {$tpl = 'store.Product.Viewed.Inner';}
if (!isset($except)) {$except = 0;} else {$except = split(",",$except);}

if($except != false) {
  $add = 1;
  foreach ($except as $value) {
		if($value == $id) {$add = 0;}
  }
}

if ($add != false) {
    if (!isset($_SESSION['viewed'])) {
    	$_SESSION['viewed'] = array($id);
	} 
	else {
		if (in_array($id, $_SESSION['viewed'])) {
			$key = array_search($id, $_SESSION['viewed']);
			unset($_SESSION['viewed'][$key]);
		}

		if (count($_SESSION['viewed']) > $limit) {
			array_shift($_SESSION['viewed']);
		}
		
		$_SESSION['viewed'][] = $id;
	}
}

if ($show == '1') {
  if (!isset($_SESSION['viewed'])) {
    return;
  }
	$ids = array_reverse($_SESSION['viewed']);
  if (empty($ids)) {
    return;
  }
}

if ($show == '1' && $snippet == false) {
  $output = '';
  foreach ($ids as $tsID) {
    if($tsID != $id) {
      $row = $modx->getObject('modResource', $tsID)->toArray();
      $output .= $modx->getChunk($tpl, $row);
    }
  }

  return $output;
}

if ($show == '1'  && $snippet != false) {
	$config = array(
		'resources' => '-'.$id.','.implode(',', $ids),
		'parents' => $parents,
		'limit' => $limit,
		'tpl' => $tpl,
		'tplOuter' => $tplOuter,
		'includeThumbs' => $thumbs
		
	);
	
	$config = array_merge($config, $scriptProperties);
  $rows = $modx->runSnippet('msProducts', $config);
	if (!empty($rows)) {
		return $modx->getChunk('store.Product.Viewed.Outer', array('title' => $title, 'rows' => $rows));
	}
	
}

if(isset($_POST['clear-list'])) $_SESSION['viewed'] = '';