112 lines
4.3 KiB
TypeScript
112 lines
4.3 KiB
TypeScript
const BERLIN_TZ = "Europe/Berlin";
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export type CalendarDate = { year: number; month: number; day: number };
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export function berlinDateKey(date: Date): string {
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const { year, month, day } = berlinParts(date);
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return `${year}-${String(month).padStart(2, "0")}-${String(day).padStart(2, "0")}`;
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}
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export function formatBerlinDate(date: Date, options: Intl.DateTimeFormatOptions = {}): string {
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return new Intl.DateTimeFormat("de-DE", { ...options, timeZone: BERLIN_TZ }).format(date);
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}
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export function formatBerlinTime(date: Date, options: Intl.DateTimeFormatOptions = {}): string {
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return new Intl.DateTimeFormat("de-DE", { ...options, timeZone: BERLIN_TZ }).format(date);
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}
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export function berlinParts(date: Date): CalendarDate & { hour: number; minute: number } {
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const parts = new Intl.DateTimeFormat("en-US", {
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timeZone: BERLIN_TZ,
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year: "numeric",
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month: "2-digit",
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day: "2-digit",
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hour: "2-digit",
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minute: "2-digit",
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hourCycle: "h23",
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}).formatToParts(date);
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const get = (type: string) => Number(parts.find((part) => part.type === type)?.value ?? "0");
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return { year: get("year"), month: get("month"), day: get("day"), hour: get("hour"), minute: get("minute") };
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}
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export function berlinOffsetMinutes(date: Date): number {
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const tzName = new Intl.DateTimeFormat("en-US", { timeZone: BERLIN_TZ, timeZoneName: "shortOffset" })
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.formatToParts(date)
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.find((part) => part.type === "timeZoneName")?.value ?? "GMT+1";
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const match = tzName.match(/GMT([+-]\d+)(?::(\d+))?/);
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const hours = match ? Number(match[1]) : 1;
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const minutes = match?.[2] ? Number(match[2]) : 0;
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return hours * 60 + (hours < 0 ? -minutes : minutes);
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}
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/** Converts a Berlin wall-clock date/time into the UTC instant it represents. */
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export function berlinWallTimeToUTC(date: CalendarDate, hour: number, minute: number): Date {
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const guess = Date.UTC(date.year, date.month - 1, date.day, hour, minute);
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return new Date(guess - berlinOffsetMinutes(new Date(guess)) * 60_000);
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}
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export function berlinDayBounds(date: Date): { key: string; start: Date; end: Date } {
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const current = berlinParts(date);
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const nextCalendarDay = new Date(Date.UTC(current.year, current.month - 1, current.day + 1));
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const next = berlinParts(nextCalendarDay);
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const start = berlinWallTimeToUTC(current, 0, 0);
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const nextStart = berlinWallTimeToUTC(next, 0, 0);
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return { key: berlinDateKey(date), start, end: new Date(nextStart.getTime() - 1) };
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}
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/**
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* Converts a JS Date (a UTC instant) into its Europe/Berlin wall-clock
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* representation for iCalendar's local `TZID` date-time form
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* (`DTSTART;TZID=Europe/Berlin:YYYYMMDDTHHMMSS`). Uses the ICU timezone
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* database via Intl rather than manual UTC+1/+2 arithmetic, so daylight
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* saving transitions are always handled correctly — no naive UTC offset
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* math that would drift by an hour half the year.
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*/
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export function toBerlinICSDateTime(date: Date): string {
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const parts = new Intl.DateTimeFormat("en-US", {
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timeZone: BERLIN_TZ,
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year: "numeric",
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month: "2-digit",
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day: "2-digit",
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hour: "2-digit",
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minute: "2-digit",
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second: "2-digit",
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hourCycle: "h23",
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}).formatToParts(date);
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const get = (type: string) => parts.find((p) => p.type === type)?.value ?? "00";
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return `${get("year")}${get("month")}${get("day")}T${get("hour")}${get("minute")}${get("second")}`;
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}
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/** UTC timestamp form (`YYYYMMDDTHHMMSSZ`) — used only for DTSTAMP, which marks generation time, not a local event time. */
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export function toUTCICSStamp(date: Date): string {
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return date.toISOString().replace(/[-:]/g, "").split(".")[0] + "Z";
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}
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/**
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* Standard IANA Europe/Berlin VTIMEZONE block (the same one commonly
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* embedded by calendar exporters): CEST from the last Sunday in March,
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* CET from the last Sunday in October — the actual EU DST rule, not an
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* approximation.
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*/
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export const BERLIN_VTIMEZONE_LINES = [
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"BEGIN:VTIMEZONE",
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"TZID:Europe/Berlin",
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"X-LIC-LOCATION:Europe/Berlin",
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"BEGIN:DAYLIGHT",
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"TZOFFSETFROM:+0100",
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"TZOFFSETTO:+0200",
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"TZNAME:CEST",
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"DTSTART:19700329T020000",
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"RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU",
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"END:DAYLIGHT",
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"BEGIN:STANDARD",
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"TZOFFSETFROM:+0200",
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"TZOFFSETTO:+0100",
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"TZNAME:CET",
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"DTSTART:19701025T030000",
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"RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU",
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"END:STANDARD",
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"END:VTIMEZONE",
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];
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