feat(api): calculate last meeting time server-side

Author: nicholaschiang

README.md

@@ -83,11 +83,10 @@ with a specific time and venue (e.g. a specific Zoom link). In order to support
   exception to a recurring meeting.
 - **Last:** The last possible meeting end time. If a meeting is recurring,
   this will be the end time of the last meeting instance in that recurring
-  range. Or, if the recurring range is infinite, we use [JavaScript's max
-  date](https://stackoverflow.com/questions/11526504/minimum-and-maximum-date)
-  (Fri Sep 12 275760) which is more than sufficient. This is calculated and
-  assigned server-side using [`rrule`](https://www.npmjs.com/package/rrule). It
-  is completely ignored client-side (in favor of the `to` property).
+  range. Or, if the recurring range is infinite, we use Firestore's max date
+  (Dec 31 9999) which is more than sufficient. This is calculated and assigned
+  server-side using [`rrule`](https://www.npmjs.com/package/rrule). It is
+  completely ignored client-side (in favor of the `to` property).
 
 Upon creation, Tutorbook sends an email to all of the `people` in the new
 meeting's match with the meeting time, venue, and everyone's contact info.

lib/api/get/last-time.ts

@@ -0,0 +1,17 @@
+import { RRule } from 'rrule';
+
+import { Timeslot } from 'lib/model';
+
+/**
+ * Get the last possible timeslot end time taking into account recurrence rules.
+ * Calculated at indexing time and used query time to filter meetings.
+ * @see {@link https://github.com/tutorbookapp/tutorbook#recurring-meetings}
+ * @see {@link https://npmjs.com/package/rrule}
+ * @see {@link https://bit.ly/3q7ZaBk}
+ */
+export default function getLastTime(time: Timeslot): Date {
+  const options = RRule.parseString(time.recur || 'RRULE:COUNT=1');
+  const rrule = new RRule({ ...options, dtstart: time.from });
+  if (!options.until && !options.count) return new Date(253402300799999);
+  return new Date((rrule.all().pop() || time.from).valueOf() + time.duration);
+}

lib/api/routes/meetings/create.ts

@@ -8,6 +8,7 @@ import createMatchSearchObj from 'lib/api/create/match-search-obj';
 import createMeetingDoc from 'lib/api/create/meeting-doc';
 import createMeetingSearchObj from 'lib/api/create/meeting-search-obj';
 import createZoom from 'lib/api/create/zoom';
+import getLastTime from 'lib/api/get/last-time';
 import getMatch from 'lib/api/get/match';
 import getOrg from 'lib/api/get/org';
 import getPeople from 'lib/api/get/people';
@@ -86,6 +87,8 @@ export default async function createMeeting(
     }
 
     body.venue = await createZoom(body, people);
+    body.time.last = getLastTime(body.time);
+
     const meeting = await createMeetingDoc(body);
     await createMeetingSearchObj(meeting);