dev_agent
0e726ac64f
Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com> Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>
82 lines
2.6 KiB
TypeScript
82 lines
2.6 KiB
TypeScript
/**
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* Local time in the application timezone.
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*
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* The admin-saved zone (settings `timezone`, an IANA name) is the single
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* source of local-time truth for the whole application; the API publishes it
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* as `effective_timezone`, naming its host's own zone when none is stored.
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* "" means the API published no zone, and only then does the browser's own
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* zone apply. Every helper takes
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* that stored value as-is; an invalid zone name throws (Intl's RangeError).
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*/
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/** The `timeZone` option for Intl: the zone, or undefined (browser) for "". */
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export function zoneOption(timeZone: string): string | undefined {
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return timeZone === "" ? undefined : timeZone;
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}
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interface WallClock {
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year: number;
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month: number;
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day: number;
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hour: number;
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minute: number;
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second: number;
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}
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function wallClock(instant: number, timeZone: string): WallClock {
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const parts = new Intl.DateTimeFormat("en-US", {
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timeZone: zoneOption(timeZone),
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hourCycle: "h23",
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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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}).formatToParts(instant);
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const part = (type: Intl.DateTimeFormatPartTypes) =>
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Number(parts.find((p) => p.type === type)?.value);
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return {
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year: part("year"),
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month: part("month"),
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day: part("day"),
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hour: part("hour"),
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minute: part("minute"),
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second: part("second"),
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};
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}
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/** The "YYYY-MM-DD" calendar date of `instant` in the zone. */
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export function isoDateIn(instant: Date, timeZone: string): string {
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const { year, month, day } = wallClock(instant.getTime(), timeZone);
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return `${year}-${String(month).padStart(2, "0")}-${String(day).padStart(2, "0")}`;
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}
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/** Today's calendar date in the zone. */
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export function todayIn(timeZone: string, now: Date = new Date()): string {
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return isoDateIn(now, timeZone);
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}
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/** The zone's UTC offset in ms at `instant` (wall clock minus UTC). */
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function offsetAt(instant: number, timeZone: string): number {
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const c = wallClock(instant, timeZone);
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const wholeSeconds = Math.floor(instant / 1000) * 1000;
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return Date.UTC(c.year, c.month - 1, c.day, c.hour, c.minute, c.second) - wholeSeconds;
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}
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/**
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* Epoch ms at which the zone's wall clock reads `hour:minute` on the
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* "YYYY-MM-DD" date. Two passes settle the offset across a DST change.
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*/
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export function wallClockInstant(
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iso: string,
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hour: number,
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minute: number,
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timeZone: string,
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): number {
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const [year, month, day] = iso.split("-").map(Number);
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const asUtc = Date.UTC(year, month - 1, day, hour, minute);
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const guess = asUtc - offsetAt(asUtc, timeZone);
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return asUtc - offsetAt(guess, timeZone);
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}
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