Fix/DST issues

apps/web/components/booking/pages/BookingPage.tsx

@@ -426,8 +426,8 @@ const BookingPage = ({
     } else {
       mutation.mutate({
         ...booking,
-        start: dayjs(date).format(),
-        end: dayjs(date).add(duration, "minute").format(),
+        start: dayjs(date).tz(timeZone()).format(),
+        end: dayjs(date).tz(timeZone()).add(duration, "minute").format(),
         eventTypeId: eventType.id,
         eventTypeSlug: eventType.slug,
         timeZone: timeZone(),

apps/web/test/lib/slots.test.ts

@@ -24,6 +24,7 @@ describe("Tests the slot logic", () => {
           },
         ],
         eventLength: 60,
+        organizerTimeZone: "America/Toronto",
       })
     ).toHaveLength(24);
   });
@@ -45,6 +46,7 @@ describe("Tests the slot logic", () => {
           },
         ],
         eventLength: 60,
+        organizerTimeZone: "America/Toronto",
       })
     ).toHaveLength(12);
   });
@@ -64,6 +66,7 @@ describe("Tests the slot logic", () => {
           },
         ],
         eventLength: 60,
+        organizerTimeZone: "America/Toronto",
       })
     ).toHaveLength(0);
   });
@@ -84,6 +87,7 @@ describe("Tests the slot logic", () => {
         minimumBookingNotice: 0,
         workingHours,
         eventLength: 60,
+        organizerTimeZone: "America/Toronto",
       })
     ).toHaveLength(0);
   });
@@ -104,6 +108,7 @@ describe("Tests the slot logic", () => {
           },
         ],
         eventLength: 60,
+        organizerTimeZone: "America/Toronto",
       })
     ).toHaveLength(11);
   });

packages/features/bookings/lib/handleNewBooking.ts

@@ -19,7 +19,7 @@ import { cancelScheduledJobs, scheduleTrigger } from "@calcom/app-store/zapier/l
 import EventManager from "@calcom/core/EventManager";
 import { getEventName } from "@calcom/core/event";
 import { getUserAvailability } from "@calcom/core/getUserAvailability";
-import type { ConfigType } from "@calcom/dayjs";
+import type { ConfigType, Dayjs } from "@calcom/dayjs";
 import dayjs from "@calcom/dayjs";
 import {
   sendAttendeeRequestEmail,
@@ -35,6 +35,7 @@ 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";
@@ -111,16 +112,40 @@ const isWithinAvailableHours = (
   timeSlot: { start: ConfigType; end: ConfigType },
   {
     workingHours,
+    organizerTimeZone,
+    inviteeTimeZone,
   }: {
     workingHours: WorkingHours[];
+    organizerTimeZone: string;
+    inviteeTimeZone: string;
   }
 ) => {
   const timeSlotStart = dayjs(timeSlot.start).utc();
   const timeSlotEnd = dayjs(timeSlot.end).utc();
+  const isOrganizerInDST = isInDST(dayjs().tz(organizerTimeZone));
+  const isInviteeInDST = isInDST(dayjs().tz(organizerTimeZone));
+  const isOrganizerInDSTWhenSlotStart = isInDST(timeSlotStart.tz(organizerTimeZone));
+  const isInviteeInDSTWhenSlotStart = isInDST(timeSlotStart.tz(inviteeTimeZone));
+  const organizerDSTDifference = getDSTDifference(organizerTimeZone);
+  const inviteeDSTDifference = getDSTDifference(inviteeTimeZone);
+const sameDSTUsers = isOrganizerInDSTWhenSlotStart === isInviteeInDSTWhenSlotStart;
+const organizerDST = isOrganizerInDST === isOrganizerInDSTWhenSlotStart;
+const inviteeDST = isInviteeInDST === isInviteeInDSTWheSlotStart;
+  const getTime = (slotTime: Dayjs, minutes: number) =>
+    slotTime
+      .startOf("day")
+      .add(
+        sameDSTUsers && organizerDST && inviteeDST
+          ? minutes
+          : minutes -
+              (isOrganizerInDSTWhenSlotStart || isOrganizerInDST
+                ? organizerDSTDifference
+                : -inviteeDSTDifference),
+        "minutes"
+      );
   for (const workingHour of workingHours) {
-    // TODO: Double check & possibly fix timezone conversions.
-    const startTime = timeSlotStart.startOf("day").add(workingHour.startTime, "minute");
-    const endTime = timeSlotEnd.startOf("day").add(workingHour.endTime, "minute");
+    const startTime = getTime(timeSlotStart, workingHour.startTime);
+    const endTime = getTime(timeSlotEnd, workingHour.endTime);
     if (
       workingHour.days.includes(timeSlotStart.day()) &&
       // UTC mode, should be performant.
@@ -247,7 +272,7 @@ async function ensureAvailableUsers(
   eventType: Awaited<ReturnType<typeof getEventTypesFromDB>> & {
     users: IsFixedAwareUser[];
   },
-  input: { dateFrom: string; dateTo: string },
+  input: { dateFrom: string; dateTo: string; timeZone: string },
   recurringDatesInfo?: {
     allRecurringDates: string[] | undefined;
     currentRecurringIndex: number | undefined;
@@ -271,6 +296,8 @@ async function ensureAvailableUsers(
         { start: input.dateFrom, end: input.dateTo },
         {
           workingHours,
+          organizerTimeZone: eventType.timeZone || eventType?.schedule?.timeZone || user.timeZone,
+          inviteeTimeZone: input.timeZone,
         }
       )
     ) {
@@ -567,6 +594,7 @@ async function handler(
       {
         dateFrom: reqBody.start,
         dateTo: reqBody.end,
+        timeZone: reqBody.timeZone,
       },
       {
         allRecurringDates,

packages/features/ee/teams/components/v2/TeamAvailabilityTimes.tsx

@@ -1,8 +1,8 @@
 import classNames from "classnames";
 import React from "react";
-import { ITimezone } from "react-timezone-select";
+import type { ITimezone } from "react-timezone-select";
 
-import { Dayjs } from "@calcom/dayjs";
+import type { Dayjs } from "@calcom/dayjs";
 import { useLocale } from "@calcom/lib/hooks/useLocale";
 import getSlots from "@calcom/lib/slots";
 import { trpc } from "@calcom/trpc/react";
@@ -42,6 +42,7 @@ export default function TeamAvailabilityTimes(props: Props) {
         workingHours: data?.workingHours || [],
         minimumBookingNotice: 0,
         eventLength: props.frequency,
+        organizerTimeZone: `${data?.timeZone}`,
       })
     : [];
 

packages/lib/date-fns/index.ts

@@ -126,3 +126,69 @@ export const isNextDayInTimezone = (time: string, timezoneA: string, timezoneB:
   const timezoneBIsLaterTimezone = sortByTimezone(timezoneA, timezoneB) === -1;
   return hoursTimezoneBIsEarlier && timezoneBIsLaterTimezone;
 };
+
+/**
+ * Dayjs does not expose the timeZone value publicly through .get("timeZone")
+ * instead, we as devs are required to somewhat hack our way to get the
+ * tz value as string
+ * @param date Dayjs
+ * @returns Time Zone name
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export const getTimeZone = (date: Dayjs): string => (date as any)["$x"]["$timezone"];
+
+/**
+ * Verify if timeZone has Daylight Saving Time (DST).
+ *
+ * Many countries in the Northern Hemisphere. Daylight Saving Time usually starts in March-April and ends in
+ * September-November when the countries return to standard time, or winter time as it is also known.
+ *
+ * In the Southern Hemisphere (south of the equator) the participating countries usually start the DST period
+ * in September-November and end DST in March-April.
+ *
+ * @param timeZone Time Zone Name (Ex. America/Mazatlan)
+ * @returns boolean
+ */
+export const timeZoneWithDST = (timeZone: string): boolean => {
+  const jan = dayjs.tz(`${new Date().getFullYear()}-01-01T00:00:00`, timeZone);
+  const jul = dayjs.tz(`${new Date().getFullYear()}-07-01T00:00:00`, timeZone);
+  return jan.utcOffset() !== jul.utcOffset();
+};
+
+/**
+ * Get DST difference.
+ * Today clocks are almost always set one hour back or ahead.
+ * However, on Lord Howe Island, Australia, clocks are set only 30 minutes forward
+ * from LHST (UTC+10:30) to LHDT (UTC+11) during DST.
+ * @param timeZone Time Zone Name (Ex. America/Mazatlan)
+ * @returns minutes
+ */
+export const getDSTDifference = (timeZone: string): number => {
+  const jan = dayjs.tz(`${new Date().getFullYear()}-01-01T00:00:00`, timeZone);
+  const jul = dayjs.tz(`${new Date().getFullYear()}-07-01T00:00:00`, timeZone);
+  return jul.utcOffset() - jan.utcOffset();
+};
+
+/**
+ * Get UTC offset of given time zone when in DST
+ * @param timeZone Time Zone Name (Ex. America/Mazatlan)
+ * @returns minutes
+ */
+export const getUTCOffsetInDST = (timeZone: string) => {
+  if (timeZoneWithDST(timeZone)) {
+    const jan = dayjs.tz(`${new Date().getFullYear()}-01-01T00:00:00`, timeZone);
+    const jul = dayjs.tz(`${new Date().getFullYear()}-07-01T00:00:00`, timeZone);
+    return jan.utcOffset() < jul.utcOffset() ? jul.utcOffset() : jan.utcOffset();
+  }
+  return 0;
+};
+/**
+ * Verifies if given time zone is in DST
+ * @param date
+ * @returns
+ */
+export const isInDST = (date: Dayjs) => {
+  const timeZone = getTimeZone(date);
+
+  return timeZoneWithDST(timeZone) && date.utcOffset() === getUTCOffsetInDST(timeZone);
+};

packages/lib/slots.ts

@@ -3,6 +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";
 
 export type GetSlots = {
   inviteeDate: Dayjs;
@@ -11,6 +12,7 @@ export type GetSlots = {
   dateOverrides?: DateOverride[];
   minimumBookingNotice: number;
   eventLength: number;
+  organizerTimeZone: string;
 };
 export type TimeFrame = { userIds?: number[]; startTime: number; endTime: number };
 
@@ -22,12 +24,16 @@ function buildSlots({
   frequency,
   eventLength,
   startDate,
+  organizerTimeZone,
+  inviteeTimeZone,
 }: {
   computedLocalAvailability: TimeFrame[];
   startOfInviteeDay: Dayjs;
   startDate: Dayjs;
   frequency: number;
   eventLength: number;
+  organizerTimeZone: string;
+  inviteeTimeZone: string;
 }) {
   // no slots today
   if (startOfInviteeDay.isBefore(startDate, "day")) {
@@ -92,11 +98,23 @@ function buildSlots({
       });
     }
   }
-  // XXX: Hack alert, as dayjs is supposedly not aware of timezone the current slot may have invalid UTC offset.
-  const timeZone =
-    (startOfInviteeDay as unknown as { $x: { $timezone: string } })["$x"]["$timezone"] || "UTC";
+
+  const isOrganizerInDST = isInDST(startOfInviteeDay.tz(organizerTimeZone));
+  const isInviteeInDST = isInDST(startOfInviteeDay.tz(inviteeTimeZone));
+  const organizerDSTDifference = getDSTDifference(organizerTimeZone);
+  const inviteeDSTDifference = getDSTDifference(inviteeTimeZone);
 
   const slots: { time: Dayjs; userIds?: number[] }[] = [];
+
+  const getTime = (time: number) => {
+    const minutes =
+      isOrganizerInDST !== isInviteeInDST
+        ? time - (isOrganizerInDST ? organizerDSTDifference : -inviteeDSTDifference)
+        : time;
+
+    return startOfInviteeDay.tz(inviteeTimeZone).add(minutes, "minutes");
+  };
+
   for (const item of Object.values(slotsTimeFrameAvailable)) {
     /*
      * @calcom/web:dev: 2022-11-06T00:00:00-04:00
@@ -108,7 +126,7 @@ function buildSlots({
      */
     const slot = {
       userIds: item.userIds,
-      time: dayjs.tz(startOfInviteeDay.add(item.startTime, "minute").format("YYYY-MM-DDTHH:mm:ss"), timeZone),
+      time: getTime(item.startTime),
     };
     // If the startOfInviteeDay has a different UTC offset than the slot, a DST change has occurred.
     // As the time has now fallen backwards, or forwards; this difference -
@@ -132,6 +150,7 @@ const getSlots = ({
   workingHours,
   dateOverrides = [],
   eventLength,
+  organizerTimeZone,
 }: GetSlots) => {
   // current date in invitee tz
   const startDate = dayjs().utcOffset(inviteeDate.utcOffset()).add(minimumBookingNotice, "minute");
@@ -151,12 +170,7 @@ const getSlots = ({
     return [];
   }
 
-  // Dayjs does not expose the timeZone value publicly through .get("timeZone")
-  // instead, we as devs are required to somewhat hack our way to get the ...
-  // tz value as string
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  const timeZone: string = (inviteeDate as any)["$x"]["$timezone"];
-
+  const timeZone: string = getTimeZone(inviteeDate);
   const workingHoursUTC = workingHours.map((schedule) => ({
     userId: schedule.userId,
     days: schedule.days,
@@ -237,6 +251,8 @@ const getSlots = ({
     startDate,
     frequency,
     eventLength,
+    organizerTimeZone,
+    inviteeTimeZone: timeZone,
   });
 };
 

packages/trpc/server/routers/viewer/slots.tsx

@@ -317,6 +317,8 @@ export async function getSchedule(input: z.infer<typeof getScheduleSchema>, ctx:
         dateOverrides,
         minimumBookingNotice: eventType.minimumBookingNotice,
         frequency: eventType.slotInterval || input.duration || eventType.length,
+        organizerTimeZone:
+          eventType.timeZone || eventType?.schedule?.timeZone || userAvailability?.[0]?.timeZone,
       })
     );
   }