fix: filter slots by requested date range to prevent date override leakage (#25822)

* fix: filter slots by requested date range to prevent date override leakage

Co-Authored-By: morgan@cal.com <morgan@cal.com>

* refactor: move filterSlotsByRequestedDateRange to private method

Co-Authored-By: morgan@cal.com <morgan@cal.com>

---------

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

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

@@ -272,6 +272,61 @@ export class AvailableSlotsService {
     return periodType === PeriodType.ROLLING_WINDOW || periodType === PeriodType.ROLLING;
   }
 
+  /**
+   * Filters slots to only include dates within the requested range.
+   * This is necessary because buildDateRanges uses a ±1 day buffer when checking
+   * if date overrides should be included (to handle timezone edge cases), which can
+   * cause slots from adjacent days to leak into the response.
+   */
+  private _filterSlotsByRequestedDateRange<
+    T extends Record<string, { time: string; attendees?: number; bookingUid?: string }[]>,
+  >({
+    slotsMappedToDate,
+    startTime,
+    endTime,
+    timeZone,
+  }: {
+    slotsMappedToDate: T;
+    startTime: string;
+    endTime: string;
+    timeZone: string | undefined;
+  }): T {
+    if (!timeZone) {
+      return slotsMappedToDate;
+    }
+    const inputStartTime = dayjs(startTime).tz(timeZone);
+    const inputEndTime = dayjs(endTime).tz(timeZone);
+
+    // fr-CA uses YYYY-MM-DD format
+    const formatter = new Intl.DateTimeFormat("fr-CA", {
+      year: "numeric",
+      month: "2-digit",
+      day: "2-digit",
+      timeZone: timeZone,
+    });
+
+    const allowedDates = new Set<string>();
+    for (
+      let d = inputStartTime.startOf("day");
+      !d.isAfter(inputEndTime, "day");
+      d = d.add(1, "day")
+    ) {
+      allowedDates.add(formatter.format(d.toDate()));
+    }
+
+    const filtered = {} as T;
+    for (const [date, slots] of Object.entries(slotsMappedToDate)) {
+      if (allowedDates.has(date)) {
+        (filtered as Record<string, typeof slots>)[date] = slots;
+      }
+    }
+    return filtered;
+  }
+  private filterSlotsByRequestedDateRange = withReporting(
+    this._filterSlotsByRequestedDateRange.bind(this),
+    "filterSlotsByRequestedDateRange"
+  );
+
   private _getAllDatesWithBookabilityStatus(availableDates: string[]) {
     const availableDatesSet = new Set(availableDates);
     const firstDate = dayjs(availableDates[0]);
@@ -1431,8 +1486,15 @@ export class AvailableSlotsService {
     );
     const withinBoundsSlotsMappedToDate = mapWithinBoundsSlotsToDate();
 
+    const filteredSlotsMappedToDate = this.filterSlotsByRequestedDateRange({
+      slotsMappedToDate: withinBoundsSlotsMappedToDate,
+      startTime: input.startTime,
+      endTime: input.endTime,
+      timeZone: input.timeZone,
+    });
+
     // We only want to run this on single targeted events and not dynamic
-    if (!Object.keys(withinBoundsSlotsMappedToDate).length && input.usernameList?.length === 1) {
+    if (!Object.keys(filteredSlotsMappedToDate).length && input.usernameList?.length === 1) {
       try {
         await this.dependencies.noSlotsNotificationService.handleNotificationWhenNoSlots({
           eventDetails: {
@@ -1474,7 +1536,7 @@ export class AvailableSlotsService {
       : null;
 
     return {
-      slots: withinBoundsSlotsMappedToDate,
+      slots: filteredSlotsMappedToDate,
       ...troubleshooterData,
     };
   }