public function init(array $config = [])
    {
        $this->setConfig($config);

        if (!empty($this->_config['groups'])) {
            sort($this->_config['groups']);
            $this->_groupPrefix = str_repeat('%s_', count($this->_config['groups']));
        }
        if (!is_numeric($this->_config['duration'])) {
            $this->_config['duration'] = strtotime($this->_config['duration']) - time();
        }

        return true;
    }