public function getPromptEmailData(SiteModel $site, EventModel $lastEvent = null)
 {
     global $CONFIG;
     $moreEventsNeeded = false;
     $checkTime = \TimeSource::getDateTime();
     if ($lastEvent) {
         $dateInterval = new \DateInterval("P" . $site->getPromptEmailsDaysInAdvance() . "D");
         $endTimeMinusExtra = clone $lastEvent->getEndAt();
         $endTimeMinusExtra->sub($dateInterval);
         if ($endTimeMinusExtra < $checkTime) {
             // there is a last event and it is before now plus whenever!
             // Now check; have we notified the user of this before?
             $dateSince = $this->getSinceDateForPromptChecking();
             if ($endTimeMinusExtra > $dateSince) {
                 // Finally check: has safe gap passed where we only send one email every X days?
                 $safeGapDays = max($site->getPromptEmailsDaysInAdvance(), $CONFIG->userWatchesPromptEmailSafeGapDays);
                 $nowMinusSafeGap = \TimeSource::getDateTime();
                 $nowMinusSafeGap->sub(new \DateInterval("P" . $safeGapDays . "D"));
                 if ($dateSince < $nowMinusSafeGap) {
                     // Finally we can agree to send an alert!
                     $moreEventsNeeded = true;
                 }
             }
         }
     }
     // TODO when add importing, need to double check this.
     return array('moreEventsNeeded' => $moreEventsNeeded, 'checkTime' => $checkTime);
 }