Record a "series parent PHID" on Calendar events that retains relationships after forks

Summary:
When you edit "X and all future events", X becomes the new parent of an event series.

Currently, it loses its relationship to its original parent. Instead, retain that relationship -- it's separate from the normal "parent", but we can use it to make the UI more clear or tweak behaviors later.

This mostly just keeps us from losing/destroying data that we might need/want later.

Test Plan:
  - Ran migrations.
  - Cancelled "X and all future events", saw sensible-appearing beahvior in the database for "seriesParentPHID".

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D16780

resources/sql/autopatches/20161031.calendar.01.seriesparent.sql

@@ -0,0 +1,5 @@
+ALTER TABLE {$NAMESPACE}_calendar.calendar_event
+  ADD seriesParentPHID VARBINARY(64);
+
+UPDATE {$NAMESPACE}_calendar.calendar_event
+  SET seriesParentPHID = instanceOfEventPHID;

src/applications/calendar/controller/PhabricatorCalendarEventCancelController.php

@@ -84,6 +84,13 @@ final class PhabricatorCalendarEventCancelController
           // NOTE: If you can't edit some of the future events, we just
           // don't try to update them. This seems like it's probably what
           // users are likely to expect.
+
+          // NOTE: This only affects events that are currently in the same
+          // series, not all events that were ever in the original series.
+          // We could use series PHIDs instead of parent PHIDs to affect more
+          // events if this turns out to be counterintuitive. Other
+          // applications differ in their behavior.
+
           $future = id(new PhabricatorCalendarEventQuery())
             ->setViewer($viewer)
             ->withParentEventPHIDs(array($event->getPHID()))

src/applications/calendar/storage/PhabricatorCalendarEvent.php

@@ -27,6 +27,7 @@ final class PhabricatorCalendarEvent extends PhabricatorCalendarDAO
 
   protected $isRecurring = 0;
 
+  protected $seriesParentPHID;
   protected $instanceOfEventPHID;
   protected $sequenceIndex;
 
@@ -140,10 +141,16 @@ final class PhabricatorCalendarEvent extends PhabricatorCalendarDAO
           'a recurring parent event!'));
     }
 
+    $series_phid = $this->getSeriesParentPHID();
+    if (!$series_phid) {
+      $series_phid = $this->getPHID();
+    }
+
     $child = id(new self())
       ->setIsCancelled(0)
       ->setIsStub(0)
       ->setInstanceOfEventPHID($this->getPHID())
+      ->setSeriesParentPHID($series_phid)
       ->setSequenceIndex($sequence)
       ->setIsRecurring(true)
       ->attachParentEvent($this)
@@ -401,6 +408,7 @@ final class PhabricatorCalendarEvent extends PhabricatorCalendarDAO
         'icon' => 'text32',
         'mailKey' => 'bytes20',
         'isRecurring' => 'bool',
+        'seriesParentPHID' => 'phid?',
         'instanceOfEventPHID' => 'phid?',
         'sequenceIndex' => 'uint32?',
         'isStub' => 'bool',
@@ -435,6 +443,9 @@ final class PhabricatorCalendarEvent extends PhabricatorCalendarDAO
           'columns' => array('instanceOfEventPHID', 'utcInstanceEpoch'),
           'unique' => true,
         ),
+        'key_series' => array(
+          'columns' => array('seriesParentPHID', 'utcInitialEpoch'),
+        ),
       ),
       self::CONFIG_SERIALIZATION => array(
         'recurrenceFrequency' => self::SERIALIZATION_JSON,