protected function updateVisitors($ip)
{
if (!$this->visitors_data) {
$this->visitors_data = $this->getData($this->visitors_file);
}
// update with current timestamp
$this->visitors_data[$ip] = time();
$visitors = $this->visitors_data;
arsort($visitors);
$count = intval($this->config->get('plugins.admin.popularity.history.visitors', 20));
$this->visitors_data = array_slice($visitors, 0, $count, true);
file_put_contents($this->visitors_file, json_encode($this->visitors_data));
}