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calcom/packages/lib/parse-zone.ts

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+import dayjs from "@calcom/dayjs";
+
+const ISO8601_OFFSET_FORMAT = /^(.*)([+-])(\d{2}):(\d{2})|(Z)$/;
+
+// @see https://github.com/iamkun/dayjs/issues/651#issuecomment-763033265
+// decorates dayjs in order to keep the utcOffset of the given date string
+// ; natively dayjs auto-converts to local time & losing utcOffset info.
+export function parseZone(
+  date?: dayjs.ConfigType,
+  format?: dayjs.OptionType,
+  locale?: string,
+  strict?: boolean
+) {
+  if (typeof date !== "string") {
+    return dayjs(date, format, locale, strict);
+  }
+  const match = date.match(ISO8601_OFFSET_FORMAT);
+  if (match === null) {
+    return;
+  }
+  if (match[0] === "Z") {
+    return dayjs(
+      date,
+      {
+        utc: true,
+        ...(typeof format === "string" ? { format } : { ...format }),
+      },
+      locale,
+      strict
+    );
+  }
+  const [, dateTime, sign, tzHour, tzMinute] = match;
+  const uOffset: number = parseInt(tzHour) * 60 + parseInt(tzMinute, 10);
+  const offset = sign === "+" ? uOffset : -uOffset;
+
+  return dayjs(
+    dateTime,
+    {
+      $offset: offset,
+      ...(typeof format === "string" ? { format } : { ...format }),
+    } as dayjs.OptionType & { $offset: number },
+    locale,
+    strict
+  );
+}