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calcom/packages/lib/date-fns/index.ts

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+import type { Dayjs } from "@calcom/dayjs";
+import dayjs from "@calcom/dayjs";
+
+// converts a date to 2022-04-25 for example.
+export const yyyymmdd = (date: Date | Dayjs) =>
+  date instanceof Date ? dayjs(date).format("YYYY-MM-DD") : date.format("YYYY-MM-DD");
+
+// @see: https://github.com/iamkun/dayjs/issues/1272 - for the reason we're not using dayjs to do this.
+export const daysInMonth = (date: Date | Dayjs) => {
+  const [year, month] =
+    date instanceof Date ? [date.getFullYear(), date.getMonth()] : [date.year(), date.month()];
+  // strange JS quirk: new Date(2022, 12, 0).getMonth() = 11
+  return new Date(year, month + 1, 0).getDate();
+};
+
+/**
+ * Expects timeFormat to be either 12 or 24, if null or undefined
+ * is passed in, we always default back to 24 hour notation.
+ */
+export const formatTime = (
+  date: string | Date | Dayjs,
+  timeFormat?: number | null,
+  timeZone?: string | null
+) => {
+  // console.log(timeZone, date);
+  return timeZone
+    ? dayjs(date)
+        .tz(timeZone)
+        .format(timeFormat === 12 ? "h:mma" : "HH:mm")
+    : dayjs(date).format(timeFormat === 12 ? "h:mma" : "HH:mm");
+};
+
+/**
+ * Checks if a provided timeZone string is recognized as a valid timezone by dayjs.
+ *
+ * @param {string} timeZone - The timezone string to be verified.
+ * @returns {boolean} - Returns 'true' if the provided timezone string is recognized as a valid timezone by dayjs. Otherwise, returns 'false'.
+ *
+ */
+export const isSupportedTimeZone = (timeZone: string) => {
+  try {
+    dayjs().tz(timeZone);
+    return true;
+  } catch (error) {
+    return false;
+  }
+};
+
+/**
+ * Returns a localized and translated date or time, based on the native
+ * Intl.DateTimeFormat available to JS. Undefined values mean the browser's
+ * locale will be used.
+ */
+export const formatLocalizedDateTime = (
+  date: Date | Dayjs,
+  options: Intl.DateTimeFormatOptions = {},
+  locale: string | undefined = undefined
+) => {
+  const theDate = date instanceof dayjs ? (date as Dayjs).toDate() : (date as Date);
+  return Intl.DateTimeFormat(locale, options).format(theDate);
+};
+
+/**
+ * Returns a localized and translated calendar day based on the
+ * given Date object and locale. Undefined values mean the defaults
+ * associated with the browser's current locale will be used.
+ */
+export const formatToLocalizedDate = (
+  date: Date | Dayjs,
+  locale: string | undefined = undefined,
+  dateStyle: Intl.DateTimeFormatOptions["dateStyle"] = "long",
+  timeZone?: string
+) => formatLocalizedDateTime(date, { dateStyle, timeZone }, locale);
+
+/**
+ * Returns a localized and translated time of day based on the
+ * given Date object and locale. Undefined values mean the defaults
+ * associated with the browser's current locale will be used.
+ */
+export const formatToLocalizedTime = (
+  date: Date | Dayjs,
+  locale: string | undefined = undefined,
+  timeStyle: Intl.DateTimeFormatOptions["timeStyle"] = "short",
+  hour12: Intl.DateTimeFormatOptions["hour12"] = undefined,
+  timeZone?: string
+) => formatLocalizedDateTime(date, { timeStyle, hour12, timeZone }, locale);
+
+/**
+ * Returns a translated timezone based on the given Date object and
+ * locale. Undefined values mean the browser's current locale
+ * will be used.
+ */
+export const formatToLocalizedTimezone = (
+  date: Date | Dayjs,
+  locale: string | undefined = undefined,
+  timeZone: Intl.DateTimeFormatOptions["timeZone"],
+  timeZoneName: Intl.DateTimeFormatOptions["timeZoneName"] = "long"
+) => {
+  // Intl.DateTimeFormat doesn't format into a timezone only, so we must
+  //  formatToParts() and return the piece we want
+  const theDate = date instanceof dayjs ? (date as Dayjs).toDate() : (date as Date);
+  return Intl.DateTimeFormat(locale, { timeZoneName, timeZone })
+    .formatToParts(theDate)
+    .find((d) => d.type == "timeZoneName")?.value;
+};
+
+/**
+ * Sorts two timezones by their offset from GMT.
+ */
+export const sortByTimezone = (timezoneA: string, timezoneB: string) => {
+  const timezoneAGmtOffset = dayjs.utc().tz(timezoneA).utcOffset();
+  const timezoneBGmtOffset = dayjs.utc().tz(timezoneB).utcOffset();
+
+  if (timezoneAGmtOffset === timezoneBGmtOffset) return 0;
+
+  return timezoneAGmtOffset < timezoneBGmtOffset ? -1 : 1;
+};
+
+/**
+ * Verifies given time is a day before in timezoneB.
+ */
+export const isPreviousDayInTimezone = (time: string, timezoneA: string, timezoneB: string) => {
+  const timeInTimezoneA = formatTime(time, 24, timezoneA);
+  const timeInTimezoneB = formatTime(time, 24, timezoneB);
+  if (time === timeInTimezoneB) return false;
+
+  // Eg timeInTimezoneA = 12:00 and timeInTimezoneB = 23:00
+  const hoursTimezoneBIsLater = timeInTimezoneB.localeCompare(timeInTimezoneA) === 1;
+  // If it is 23:00, does timezoneA come before or after timezoneB in GMT?
+  const timezoneBIsEarlierTimezone = sortByTimezone(timezoneA, timezoneB) === 1;
+  return hoursTimezoneBIsLater && timezoneBIsEarlierTimezone;
+};
+
+/**
+ * Verifies given time is a day after in timezoneB.
+ */
+export const isNextDayInTimezone = (time: string, timezoneA: string, timezoneB: string) => {
+  const timeInTimezoneA = formatTime(time, 24, timezoneA);
+  const timeInTimezoneB = formatTime(time, 24, timezoneB);
+  if (time === timeInTimezoneB) return false;
+
+  // Eg timeInTimezoneA = 12:00 and timeInTimezoneB = 09:00
+  const hoursTimezoneBIsEarlier = timeInTimezoneB.localeCompare(timeInTimezoneA) === -1;
+  // If it is 09:00, does timezoneA come before or after timezoneB in GMT?
+  const timezoneBIsLaterTimezone = sortByTimezone(timezoneA, timezoneB) === -1;
+  return hoursTimezoneBIsEarlier && timezoneBIsLaterTimezone;
+};
+
+const weekDays = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"] as const;
+export type WeekDays = (typeof weekDays)[number];
+type WeekDayIndex = 0 | 1 | 2 | 3 | 4 | 5 | 6;
+
+/**
+ * Turns weekday string (eg "Monday") into a number (eg 1).
+ * Also accepts a number as parameter (and straight returns that), and accepts
+ * undefined as a parameter; returns 0 in that case.
+ */
+export const weekdayToWeekIndex = (weekday: WeekDays | string | number | undefined) => {
+  if (typeof weekday === "undefined") return 0;
+  if (typeof weekday === "number") return weekday >= 0 && weekday >= 6 ? (weekday as WeekDayIndex) : 0;
+  return (weekDays.indexOf(weekday as WeekDays) as WeekDayIndex) || 0;
+};
+
+/**
+ * Dayjs does not expose the timeZone value publicly through .get("timeZone")
+ * instead, we as devs are required to somewhat hack our way to get the
+ * tz value as string
+ * @param date Dayjs
+ * @returns Time Zone name
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export const getTimeZone = (date: Dayjs): string => (date as any)["$x"]["$timezone"];
+
+/**
+ * Verify if timeZone has Daylight Saving Time (DST).
+ *
+ * Many countries in the Northern Hemisphere. Daylight Saving Time usually starts in March-April and ends in
+ * September-November when the countries return to standard time, or winter time as it is also known.
+ *
+ * In the Southern Hemisphere (south of the equator) the participating countries usually start the DST period
+ * in September-November and end DST in March-April.
+ *
+ * @param timeZone Time Zone Name (Ex. America/Mazatlan)
+ * @returns boolean
+ */
+export const timeZoneWithDST = (timeZone: string): boolean => {
+  const jan = dayjs.tz(`${new Date().getFullYear()}-01-01T00:00:00`, timeZone);
+  const jul = dayjs.tz(`${new Date().getFullYear()}-07-01T00:00:00`, timeZone);
+  return jan.utcOffset() !== jul.utcOffset();
+};
+
+/**
+ * Get DST difference.
+ * Today clocks are almost always set one hour back or ahead.
+ * However, on Lord Howe Island, Australia, clocks are set only 30 minutes forward
+ * from LHST (UTC+10:30) to LHDT (UTC+11) during DST.
+ * @param timeZone Time Zone Name (Ex. America/Mazatlan)
+ * @returns minutes
+ */
+export const getDSTDifference = (timeZone: string): number => {
+  const jan = dayjs.tz(`${new Date().getFullYear()}-01-01T00:00:00`, timeZone);
+  const jul = dayjs.tz(`${new Date().getFullYear()}-07-01T00:00:00`, timeZone);
+  return jul.utcOffset() - jan.utcOffset();
+};
+
+/**
+ * Get UTC offset of given time zone when in DST
+ * @param timeZone Time Zone Name (Ex. America/Mazatlan)
+ * @returns minutes
+ */
+export const getUTCOffsetInDST = (timeZone: string) => {
+  if (timeZoneWithDST(timeZone)) {
+    const jan = dayjs.tz(`${new Date().getFullYear()}-01-01T00:00:00`, timeZone);
+    const jul = dayjs.tz(`${new Date().getFullYear()}-07-01T00:00:00`, timeZone);
+    return jan.utcOffset() < jul.utcOffset() ? jul.utcOffset() : jan.utcOffset();
+  }
+  return 0;
+};
+/**
+ * Verifies if given time zone is in DST
+ * @param date
+ * @returns
+ */
+export const isInDST = (date: Dayjs) => {
+  const timeZone = getTimeZone(date);
+
+  return timeZoneWithDST(timeZone) && date.utcOffset() === getUTCOffsetInDST(timeZone);
+};
+
+/**
+ * Get UTC offset of given time zone
+ * @param timeZone Time Zone Name (Ex. America/Mazatlan)
+ * @param date
+ * @returns
+ */
+export function getUTCOffsetByTimezone(timeZone: string, date?: string | Date | Dayjs) {
+  if (!timeZone) return null;
+
+  return dayjs(date).tz(timeZone).utcOffset();
+}