fix: '/slots' endpoint API fixes (calcom#12693)

apps/api/pages/api/slots/_get.ts

@@ -1,5 +1,9 @@
+import timezone from "dayjs/plugin/timezone";
+import utc from "dayjs/plugin/utc";
 import type { NextApiRequest, NextApiResponse } from "next";
 
+import dayjs from "@calcom/dayjs";
+import { isSupportedTimeZone } from "@calcom/lib/date-fns";
 import { HttpError } from "@calcom/lib/http-error";
 import { defaultResponder } from "@calcom/lib/server";
 import { createContext } from "@calcom/trpc/server/createContext";
@@ -9,10 +13,34 @@ import { getAvailableSlots } from "@calcom/trpc/server/routers/viewer/slots/util
 import { TRPCError } from "@trpc/server";
 import { getHTTPStatusCodeFromError } from "@trpc/server/http";
 
+// Apply plugins
+dayjs.extend(utc);
+dayjs.extend(timezone);
+
 async function handler(req: NextApiRequest, res: NextApiResponse) {
   try {
-    const input = getScheduleSchema.parse(req.query);
-    return await getAvailableSlots({ ctx: await createContext({ req, res }), input });
+    const { usernameList, ...rest } = req.query;
+    let slugs = usernameList;
+    if (!Array.isArray(usernameList)) {
+      slugs = usernameList ? [usernameList] : [];
+    }
+    const input = getScheduleSchema.parse({ usernameList: slugs, ...rest });
+    const timeZoneSupported = input.timeZone ? isSupportedTimeZone(input.timeZone) : false;
+    const availableSlots = await getAvailableSlots({ ctx: await createContext({ req, res }), input });
+    const slotsInProvidedTimeZone = timeZoneSupported
+      ? Object.keys(availableSlots.slots).reduce(
+          (acc: Record<string, { time: string; attendees?: number; bookingUid?: string }[]>, date) => {
+            acc[date] = availableSlots.slots[date].map((slot) => ({
+              ...slot,
+              time: dayjs(slot.time).tz(input.timeZone).format(),
+            }));
+            return acc;
+          },
+          {}
+        )
+      : availableSlots;
+
+    return slotsInProvidedTimeZone;
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
   } catch (cause) {
     if (cause instanceof TRPCError) {