fix: align booking limit timezone between availability and validation (calcom#24846)

* fix: align booking limit timezone between availability and validation

- Use eventType.schedule?.timeZone for booking limits in availability calculation
- Previously used user's timezone causing day boundary mismatch
- Add unit tests to verify timezone alignment
- Fixes issue where slots remain available after reaching booking limit

Co-Authored-By: anik@cal.com <adhabal2002@gmail.com>

* Rename variable limitsTz to eventTimeZone

* update

* fix: correct timezone fallback to include user timezone without forcing UTC

- Changed fallback chain to: schedule → event → user → undefined
- Treats empty strings as missing timezones
- Does not force UTC when all timezones are missing
- Aligns with validation behavior when timezone is undefined
- Fixes getSchedule.test.ts failures

Co-Authored-By: anik@cal.com <adhabal2002@gmail.com>

* Revert "fix: correct timezone fallback to include user timezone without forcing UTC"

This reverts commit 721e0bd.

* test: remove complex unit tests with 'as any' casts

- Removed Booking Limits Timezone Alignment tests that required heavy mocking
- These tests relied on spying private methods and had many 'as any' casts
- Timezone alignment is already covered by integration tests in getSchedule.test.ts
- Kept BookingDateInPastError test which has no type issues

Co-Authored-By: anik@cal.com <adhabal2002@gmail.com>

* address review

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: anikdhabal

apps/web/test/lib/getSchedule.test.ts

@@ -2735,6 +2735,103 @@ describe("getSchedule", () => {
       expect(availableSlotsInTz.filter((slot) => slot.format().startsWith(plus2DateString)).length).toBe(0); // 1 booking per day as limit
     });
 
+    test("booking limits use schedule timezone when set, falling back to user timezone", async () => {
+      const { dateString: plus1DateString } = getDate({ dateIncrement: 1 });
+      const { dateString: plus2DateString } = getDate({ dateIncrement: 2 });
+      const { dateString: plus3DateString } = getDate({ dateIncrement: 3 });
+
+      const scenarioData = {
+        eventTypes: [
+          {
+            id: 1,
+            length: 60,
+            beforeEventBuffer: 0,
+            afterEventBuffer: 0,
+            bookingLimits: {
+              PER_DAY: 1,
+            },
+            schedule: {
+              id: 1,
+              name: "Schedule with timezone",
+              availability: [
+                {
+                  userId: null,
+                  eventTypeId: null,
+                  days: [0, 1, 2, 3, 4, 5, 6],
+                  startTime: new Date("1970-01-01T00:00:00.000Z"),
+                  endTime: new Date("1970-01-01T23:59:59.999Z"),
+                  date: null,
+                },
+              ],
+              timeZone: Timezones["+5:30"],
+            },
+            users: [
+              {
+                id: 101,
+              },
+            ],
+          },
+        ],
+        users: [
+          {
+            ...TestData.users.example,
+            id: 101,
+            schedules: [
+              {
+                id: 2,
+                name: "User schedule",
+                availability: [
+                  {
+                    userId: null,
+                    eventTypeId: null,
+                    days: [0, 1, 2, 3, 4, 5, 6],
+                    startTime: new Date("1970-01-01T00:00:00.000Z"),
+                    endTime: new Date("1970-01-01T23:59:59.999Z"),
+                    date: null,
+                  },
+                ],
+                timeZone: Timezones["+6:00"],
+              },
+            ],
+          },
+        ],
+        bookings: [
+          {
+            userId: 101,
+            eventTypeId: 1,
+            startTime: `${plus2DateString}T08:00:00.000Z`,
+            endTime: `${plus2DateString}T09:00:00.000Z`,
+            status: "ACCEPTED" as BookingStatus,
+          },
+        ],
+      };
+
+      await createBookingScenario(scenarioData);
+
+      const availability = await availableSlotsService.getAvailableSlots({
+        input: {
+          eventTypeId: 1,
+          eventTypeSlug: "",
+          startTime: `${plus1DateString}T00:00:00.000Z`,
+          endTime: `${plus3DateString}T23:59:59.999Z`,
+          timeZone: Timezones["+5:30"],
+          isTeamEvent: false,
+          orgSlug: null,
+        },
+      });
+
+      const availableSlotsInScheduleTz: dayjs.Dayjs[] = [];
+      for (const date in availability.slots) {
+        availability.slots[date].forEach((timeObj) => {
+          availableSlotsInScheduleTz.push(dayjs(timeObj.time).tz(Timezones["+5:30"]));
+        });
+      }
+
+      expect(availableSlotsInScheduleTz.filter((slot) => slot.format().startsWith(plus2DateString)).length).toBe(
+        0
+      );
+    });
+
     test("a slot counts as being busy when the eventType is requiresConfirmation and requiresConfirmationWillBlockSlot", async () => {
       const { dateString: plus1DateString } = getDate({ dateIncrement: 1 });
       const { dateString: plus2DateString } = getDate({ dateIncrement: 2 });

packages/trpc/server/routers/viewer/slots/util.ts

@@ -823,6 +823,7 @@ export class AvailableSlotsService {
     let busyTimesFromLimitsMap: Map<number, EventBusyDetails[]> | undefined = undefined;
     if (eventType && (bookingLimits || durationLimits)) {
       const usersForLimits = usersWithCredentials.map((user) => ({ id: user.id, email: user.email }));
+      const eventTimeZone = eventType.schedule?.timeZone ?? usersWithCredentials[0]?.timeZone ?? "UTC";
       busyTimesFromLimitsMap = await this.getBusyTimesFromLimitsForUsers(
         usersForLimits,
         bookingLimits,
@@ -831,7 +832,7 @@ export class AvailableSlotsService {
         endTime,
         typeof input.duration === "number" ? input.duration : undefined,
         eventType,
-        usersWithCredentials[0]?.timeZone || "UTC",
+        eventTimeZone,
         input.rescheduleUid || undefined
       );
     }
@@ -845,14 +846,15 @@ export class AvailableSlotsService {
     let teamBookingLimitsMap: Map<number, EventBusyDetails[]> | undefined = undefined;
     if (teamForBookingLimits && teamBookingLimits) {
       const usersForTeamLimits = usersWithCredentials.map((user) => ({ id: user.id, email: user.email }));
+      const eventTimeZone = eventType.schedule?.timeZone ?? usersWithCredentials[0]?.timeZone ?? "UTC";
       teamBookingLimitsMap = await this.getBusyTimesFromTeamLimitsForUsers(
         usersForTeamLimits,
         teamBookingLimits,
         startTime,
         endTime,
         teamForBookingLimits.id,
         teamForBookingLimits.includeManagedEventsInLimits,
-        usersWithCredentials[0]?.timeZone || "UTC",
+        eventTimeZone,
         input.rescheduleUid || undefined
       );
     }