From 9ba13a3f3cf5aa0a3a979c293b63019afd2edaf2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Efra=C3=ADn=20Roch=C3=ADn?= <roae.85@gmail.com>
Date: Fri, 17 Mar 2023 04:53:05 -0700
Subject: [PATCH] Amend logic to calc slots time already in DST (#7792)

* amend logic to calculate DST time on buildSlots

* send start and end date in UTC

* port the logic to calc DST from buildSlots to inWithinAvailableHours
---
 .../web/components/booking/pages/BookingPage.tsx |  8 ++++----
 .../features/bookings/lib/handleNewBooking.ts    | 11 ++++-------
 packages/lib/slots.ts                            | 16 +++++++---------
 3 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/apps/web/components/booking/pages/BookingPage.tsx b/apps/web/components/booking/pages/BookingPage.tsx
index 8aa1573d83..92346c5716 100644
--- a/apps/web/components/booking/pages/BookingPage.tsx
+++ b/apps/web/components/booking/pages/BookingPage.tsx
@@ -448,8 +448,8 @@ const BookingPage = ({
       const recurringEventId = uuidv4();
       const recurringBookings = recurringDates.map((recurringDate) => ({
         ...bookingValues,
-        start: dayjs(recurringDate).format(),
-        end: dayjs(recurringDate).add(duration, "minute").format(),
+        start: dayjs(recurringDate).utc().format(),
+        end: dayjs(recurringDate).utc().add(duration, "minute").format(),
         eventTypeId: eventType.id,
         eventTypeSlug: eventType.slug,
         recurringEventId,
@@ -468,8 +468,8 @@ const BookingPage = ({
     } else {
       mutation.mutate({
         ...bookingValues,
-        start: dayjs(date).tz(timeZone()).format(),
-        end: dayjs(date).tz(timeZone()).add(duration, "minute").format(),
+        start: dayjs(date).utc().format(),
+        end: dayjs(date).utc().add(duration, "minute").format(),
         eventTypeId: eventType.id,
         eventTypeSlug: eventType.slug,
         timeZone: timeZone(),
diff --git a/packages/features/bookings/lib/handleNewBooking.ts b/packages/features/bookings/lib/handleNewBooking.ts
index 89e7f82dcb..2e5744dcb6 100644
--- a/packages/features/bookings/lib/handleNewBooking.ts
+++ b/packages/features/bookings/lib/handleNewBooking.ts
@@ -38,7 +38,6 @@ import { deleteScheduledSMSReminder } from "@calcom/features/ee/workflows/lib/re
 import getWebhooks from "@calcom/features/webhooks/lib/getWebhooks";
 import { isPrismaObjOrUndefined, parseRecurringEvent } from "@calcom/lib";
 import { getVideoCallUrl } from "@calcom/lib/CalEventParser";
-import { getDSTDifference, isInDST } from "@calcom/lib/date-fns";
 import { getDefaultEvent, getGroupName, getUsernameList } from "@calcom/lib/defaultEvents";
 import { getErrorFromUnknown } from "@calcom/lib/errors";
 import getPaymentAppData from "@calcom/lib/getPaymentAppData";
@@ -125,13 +124,11 @@ const isWithinAvailableHours = (
 ) => {
   const timeSlotStart = dayjs(timeSlot.start).utc();
   const timeSlotEnd = dayjs(timeSlot.end).utc();
-  const isOrganizerInDSTWhenSlotStart = isInDST(timeSlotStart.tz(organizerTimeZone));
-  const organizerDSTDifference = getDSTDifference(organizerTimeZone);
+  const organizerDSTDiff =
+    dayjs().tz(organizerTimeZone).utcOffset() - timeSlotStart.tz(organizerTimeZone).utcOffset();
+  const getTime = (slotTime: Dayjs, minutes: number) =>
+    slotTime.startOf("day").add(minutes + organizerDSTDiff, "minutes");
 
-  const getTime = (slotTime: Dayjs, minutes: number) => {
-    const minutesDTS = isOrganizerInDSTWhenSlotStart ? minutes - organizerDSTDifference : minutes;
-    return slotTime.startOf("day").add(minutesDTS, "minutes");
-  };
   for (const workingHour of workingHours) {
     const startTime = getTime(timeSlotStart, workingHour.startTime);
     const endTime = getTime(timeSlotEnd, workingHour.endTime);
diff --git a/packages/lib/slots.ts b/packages/lib/slots.ts
index 57cf50112b..3ec13df18b 100644
--- a/packages/lib/slots.ts
+++ b/packages/lib/slots.ts
@@ -3,7 +3,7 @@ import dayjs from "@calcom/dayjs";
 import type { WorkingHours, TimeRange as DateOverride } from "@calcom/types/schedule";
 
 import { getWorkingHours } from "./availability";
-import { getTimeZone, isInDST, getDSTDifference } from "./date-fns";
+import { getTimeZone } from "./date-fns";
 
 export type GetSlots = {
   inviteeDate: Dayjs;
@@ -99,15 +99,13 @@ function buildSlots({
     }
   }
 
-  const isOrganizerInDST = isInDST(startOfInviteeDay.tz(organizerTimeZone));
-  const isInviteeInDST = isInDST(startOfInviteeDay.tz(inviteeTimeZone));
-  const organizerDSTDifference = getDSTDifference(organizerTimeZone);
-  const inviteeDSTDifference = getDSTDifference(inviteeTimeZone);
-
+  const organizerDSTDiff =
+    dayjs().tz(organizerTimeZone).utcOffset() - startOfInviteeDay.tz(organizerTimeZone).utcOffset();
+  const inviteeDSTDiff =
+    dayjs().tz(inviteeTimeZone).utcOffset() - startOfInviteeDay.tz(inviteeTimeZone).utcOffset();
   const slots: { time: Dayjs; userIds?: number[] }[] = [];
-  const resultDSTDifference = isOrganizerInDST ? organizerDSTDifference : -inviteeDSTDifference;
   const getTime = (time: number) => {
-    const minutes = isOrganizerInDST !== isInviteeInDST ? time - resultDSTDifference : time;
+    const minutes = time + organizerDSTDiff - inviteeDSTDiff;
 
     return startOfInviteeDay.tz(inviteeTimeZone).add(minutes, "minutes");
   };
@@ -152,7 +150,7 @@ const getSlots = ({
   // checks if the start date is in the past
 
   /**
-   *  TODO: change "day" for "hour" to stop displaying 1 day before today
+   * TODO: change "day" for "hour" to stop displaying 1 day before today
    * This is displaying a day as available as sometimes difference between two dates is < 24 hrs.
    * But when doing timezones an available day for an owner can be 2 days available in other users tz.
    *