first commit

calcom/packages/platform/atoms/hooks/useTimezone.ts

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+import { useEffect } from "react";
+
+import dayjs from "@calcom/dayjs";
+
+import { useMe } from "./useMe";
+
+export const useTimezone = (
+  onTimeZoneChange?: (currentTimezone: string) => void,
+  currentTimezone: string = dayjs.tz.guess()
+) => {
+  const { data: me, isLoading } = useMe();
+  const preferredTimezone = me?.data?.timeZone ?? currentTimezone;
+
+  useEffect(() => {
+    if (!isLoading && preferredTimezone && onTimeZoneChange && preferredTimezone !== currentTimezone) {
+      onTimeZoneChange(currentTimezone);
+    }
+  }, [currentTimezone, preferredTimezone, onTimeZoneChange, isLoading]);
+};