97 lines
3.2 KiB
TypeScript
97 lines
3.2 KiB
TypeScript
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/**
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* Utilities for overnight pause windows.
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* Works in both Node.js and browser — uses only Intl, no extra dependencies.
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*/
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function getLocalMinutes(timezone: string, now: Date): number {
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const formatter = new Intl.DateTimeFormat("en-US", {
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timeZone: timezone,
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hour: "2-digit",
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minute: "2-digit",
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hour12: false,
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});
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const parts = formatter.formatToParts(now);
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const hour = parseInt(parts.find((p) => p.type === "hour")?.value ?? "0", 10);
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const minute = parseInt(parts.find((p) => p.type === "minute")?.value ?? "0", 10);
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// Intl hour12:false can return "24" for midnight — normalize to 0
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return (hour === 24 ? 0 : hour) * 60 + minute;
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}
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/**
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* Build a UTC Date representing "the given date at HH:MM in the given timezone."
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* Corrects for the UTC offset by comparing what local time the naive UTC produces.
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*/
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function utcForLocalTime(
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timezone: string,
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year: number,
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month: number, // 1-indexed
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day: number,
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hour: number,
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minute: number
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): Date {
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// Start with a naive UTC (treating target H:M as UTC)
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const approxUTC = Date.UTC(year, month - 1, day, hour, minute, 0);
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const probe = new Date(approxUTC);
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const localMins = getLocalMinutes(timezone, probe);
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const targetMins = hour * 60 + minute;
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// Shift: if local is behind target, add the gap; if ahead, subtract it
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return new Date(approxUTC + (targetMins - localMins) * 60 * 1000);
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}
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/**
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* Returns true if `now` falls inside the overnight pause window defined by
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* startHHMM–endHHMM in the given IANA timezone.
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*
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* The window almost always spans midnight (e.g. "23:00"–"07:00"), but a
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* same-day window (e.g. "10:00"–"18:00") is also handled correctly.
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*/
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export function isInOvernightWindow(
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timezone: string,
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startHHMM: string,
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endHHMM: string,
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now = new Date()
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): boolean {
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const currentMinutes = getLocalMinutes(timezone, now);
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const [sh, sm] = startHHMM.split(":").map(Number);
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const [eh, em] = endHHMM.split(":").map(Number);
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const startMinutes = sh * 60 + sm;
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const endMinutes = eh * 60 + em;
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if (startMinutes > endMinutes) {
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// Spans midnight: in window if current >= start OR current < end
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return currentMinutes >= startMinutes || currentMinutes < endMinutes;
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}
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// Same-day window: in window if start <= current < end
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return currentMinutes >= startMinutes && currentMinutes < endMinutes;
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}
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/**
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* Returns the next UTC Date when endHHMM will occur in the given timezone.
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* Used to tell clients when the overnight window will end.
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*/
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export function getOvernightResumeUTC(
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timezone: string,
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endHHMM: string,
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now = new Date()
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): Date {
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const [eh, em] = endHHMM.split(":").map(Number);
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// Get current calendar date in the target timezone
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const dateFmt = new Intl.DateTimeFormat("en-CA", {
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timeZone: timezone,
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year: "numeric",
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month: "2-digit",
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day: "2-digit",
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});
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const [year, month, day] = dateFmt.format(now).split("-").map(Number);
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// Candidate: today at endHHMM in the target timezone
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const candidate = utcForLocalTime(timezone, year, month, day, eh, em);
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// If this moment has already passed, advance one day
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if (candidate.getTime() <= now.getTime()) {
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return new Date(candidate.getTime() + 24 * 60 * 60 * 1000);
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}
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return candidate;
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}
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