Respect "End Date" for recurring Calendar events in detail UI

Summary:
Fixes T11396. Currently, you can keep clicking "Next >" forever to generate infinite instances of an event, even if it has a set end date.

Likewise, you can visit `/E123/999999` or whatever to stub out the 999999th instance of an event.

Instead:

  - Before creating a new stub, make sure it happens before any end date.
  - 404 stubs if we can't create them.
  - Disable the "Next >" button if it isn't valid.

Test Plan:
  - Visited `/E123/9999` for an event with a recurrence end date, got 404.
  - Clicked "Next >" on an event with an end date, got new events until I hit the end date.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11396

Differential Revision: https://secure.phabricator.com/D16517

src/applications/calendar/controller/PhabricatorCalendarEventViewController.php

@@ -278,7 +278,14 @@ final class PhabricatorCalendarEventViewController
       $parent = $event->getParentEvent();
     }
 
-    $next_uri = $parent->getURI().'/'.($sequence + 1);
+    if ($parent->isValidSequenceIndex($viewer, $sequence + 1)) {
+      $next_uri = $parent->getURI().'/'.($sequence + 1);
+      $has_next = true;
+    } else {
+      $next_uri = null;
+      $has_next = false;
+    }
+
     if ($sequence) {
       if ($sequence > 1) {
         $previous_uri = $parent->getURI().'/'.($sequence - 1);
@@ -302,6 +309,7 @@ final class PhabricatorCalendarEventViewController
       ->setTag('a')
       ->setIcon('fa-chevron-right')
       ->setHref($next_uri)
+      ->setDisabled(!$has_next)
       ->setText(pht('Next'));
 
     $header
@@ -450,9 +458,11 @@ final class PhabricatorCalendarEventViewController
           'it.'));
     }
 
-    $instance = $event->newStub($viewer, $sequence);
+    if (!$event->isValidSequenceIndex($viewer, $sequence)) {
+      return null;
+    }
 
-    return $instance;
+    return $event->newStub($viewer, $sequence);
   }
 
   private function buildSubheaderView(PhabricatorCalendarEvent $event) {

src/applications/calendar/storage/PhabricatorCalendarEvent.php

@@ -137,7 +137,8 @@ final class PhabricatorCalendarEvent extends PhabricatorCalendarDAO
     );
 
     // Read these fields from the parent event instead of this event. For
-    // example, we want any changes to the parent event's name to
+    // example, we want any changes to the parent event's name to apply to
+    // the child.
     if (isset($inherit[$field])) {
       if ($this->getIsStub()) {
         // TODO: This should be unconditional, but the execution order of
@@ -171,33 +172,66 @@ final class PhabricatorCalendarEvent extends PhabricatorCalendarDAO
       ->setName($parent->getName())
       ->setDescription($parent->getDescription());
 
-    $frequency = $parent->getFrequencyUnit();
-    $modify_key = '+'.$this->getSequenceIndex().' '.$frequency;
+    $sequence = $this->getSequenceIndex();
+    $duration = $this->getDuration();
+    $epochs = $parent->getSequenceIndexEpochs($actor, $sequence, $duration);
 
-    $date = $parent->getDateFrom();
-    $date_time = PhabricatorTime::getDateTimeFromEpoch($date, $actor);
+    $this
+      ->setDateFrom($epochs['dateFrom'])
+      ->setDateTo($epochs['dateTo'])
+      ->setAllDayDateFrom($epochs['allDayDateFrom'])
+      ->setAllDayDateTo($epochs['allDayDateTo']);
+
+    return $this;
+  }
+
+  public function isValidSequenceIndex(PhabricatorUser $viewer, $sequence) {
+    try {
+      $this->getSequenceIndexEpochs($viewer, $sequence, $this->getDuration());
+      return true;
+    } catch (Exception $ex) {
+      return false;
+    }
+  }
+
+  private function getSequenceIndexEpochs(
+    PhabricatorUser $viewer,
+    $sequence,
+    $duration) {
+
+    $frequency = $this->getFrequencyUnit();
+    $modify_key = '+'.$sequence.' '.$frequency;
+
+    $date = $this->getDateFrom();
+    $date_time = PhabricatorTime::getDateTimeFromEpoch($date, $viewer);
     $date_time->modify($modify_key);
     $date = $date_time->format('U');
 
-    $duration = $this->getDuration();
+    $end_date = $this->getRecurrenceEndDate();
+    if ($end_date && $date > $end_date) {
+      throw new Exception(
+        pht(
+          'Sequence "%s" is invalid for this event: it would occur after '.
+          'the event stops repeating.',
+          $sequence));
+    }
 
     $utc = new DateTimeZone('UTC');
 
-    $allday_from = $parent->getAllDayDateFrom();
+    $allday_from = $this->getAllDayDateFrom();
     $allday_date = new DateTime('@'.$allday_from, $utc);
     $allday_date->setTimeZone($utc);
     $allday_date->modify($modify_key);
 
     $allday_min = $allday_date->format('U');
-    $allday_duration = ($parent->getAllDayDateTo() - $allday_from);
+    $allday_duration = ($this->getAllDayDateTo() - $allday_from);
 
-    $this
-      ->setDateFrom($date)
-      ->setDateTo($date + $duration)
-      ->setAllDayDateFrom($allday_min)
-      ->setAllDayDateTo($allday_min + $allday_duration);
-
-    return $this;
+    return array(
+      'dateFrom' => $date,
+      'dateTo' => $date + $duration,
+      'allDayDateFrom' => $allday_min,
+      'allDayDateTo' => $allday_min + $allday_duration,
+    );
   }
 
   public function newStub(PhabricatorUser $actor, $sequence) {