public static function getChats($chat_id, $role, $timestamp_last_update = null)
{
$chatline = new ChatLine(array());
$options = array('first_id' => $chat_id, 'role' => $role, 'since' => $timestamp_last_update, 'limit_paging' => 20);
$chats = $chatline->get($options);
return $chats;
}
