public function completedAssessmentsData()
    {
        $timePeriod = $this->getRequestParameter('interval');

        $eventLog = $this->getServiceLocator()->get(\oat\taoEventLog\model\eventLog\LoggerService::SERVICE_ID);

        $tz = new \DateTimeZone(\common_session_SessionManager::getSession()->getTimeZone());
        $timeKeys = $this->getTimeKeys($timePeriod);
        $interval = $this->getInterval($timePeriod);

        foreach ($timeKeys as $timeKey) {
            $to = clone($timeKey);
            $from = clone($to);
            $from->sub($interval);
            $countEvents = $eventLog->count([
                ['occurred', 'between', $from->format('Y-m-d H:i:s'), $to->format('Y-m-d H:i:s')],
                ['event_name', '=', DeliveryExecutionFinished::class],
            ]);
            $result['time'][] = $to->setTimezone($tz)->format('Y-m-d H:i:s');
            $result['amount'][] = $countEvents;
        }

        $this->returnJson($result, 200);
    }