1.0.37

src/lib/utils/date-format.ts

@@ -82,3 +82,75 @@ export function formatTimePartWith(
 			: `${hour24}:${minutes}`;
 	}
 }
+
+/**
+ * Offset of a timezone from UTC (in ms) at a given instant.
+ * Positive for zones ahead of UTC (e.g. UTC+2 -> 7_200_000).
+ */
+function tzOffsetMs(timeZone: string, at: Date): number {
+	const dtf = new Intl.DateTimeFormat('en-US', {
+		timeZone,
+		hourCycle: 'h23',
+		year: 'numeric',
+		month: '2-digit',
+		day: '2-digit',
+		hour: '2-digit',
+		minute: '2-digit',
+		second: '2-digit'
+	});
+	const parts = dtf.formatToParts(at);
+	const get = (type: Intl.DateTimeFormatPartTypes) =>
+		parseInt(parts.find((p) => p.type === type)?.value ?? '0', 10);
+	const asUtc = Date.UTC(get('year'), get('month') - 1, get('day'), get('hour'), get('minute'), get('second'));
+	// Drop sub-second precision of `at` - formatToParts only has seconds
+	return asUtc - Math.floor(at.getTime() / 1000) * 1000;
+}
+
+/**
+ * Current calendar date in a timezone as 'YYYY-MM-DD'.
+ * Falsy timeZone means the browser's local timezone.
+ */
+export function currentDateInTimezone(timeZone?: string): string {
+	const now = new Date();
+	if (!timeZone) {
+		const y = now.getFullYear();
+		const m = String(now.getMonth() + 1).padStart(2, '0');
+		const d = String(now.getDate()).padStart(2, '0');
+		return `${y}-${m}-${d}`;
+	}
+	const parts = new Intl.DateTimeFormat('en-CA', {
+		timeZone,
+		year: 'numeric',
+		month: '2-digit',
+		day: '2-digit'
+	}).formatToParts(now);
+	const get = (type: Intl.DateTimeFormatPartTypes) => parts.find((p) => p.type === type)?.value ?? '';
+	return `${get('year')}-${get('month')}-${get('day')}`;
+}
+
+/**
+ * UTC instant (ISO string) of a day boundary in a timezone: midnight for the
+ * start of the day, 23:59:59.999 for the end. Used to turn date-only filter
+ * values ('YYYY-MM-DD', meaning a day in the user's configured timezone) into
+ * timestamps comparable against UTC-stored event times (#1269).
+ * Falsy timeZone means the browser's local timezone.
+ */
+export function dayBoundaryToUtcISO(dateStr: string, timeZone: string | undefined, endOfDay: boolean): string {
+	const [y, m, d] = dateStr.split('-').map(Number);
+	const h = endOfDay ? 23 : 0;
+	const min = endOfDay ? 59 : 0;
+	const s = endOfDay ? 59 : 0;
+	const ms = endOfDay ? 999 : 0;
+
+	if (!timeZone) {
+		return new Date(y, m - 1, d, h, min, s, ms).toISOString();
+	}
+
+	const wallClockUtc = Date.UTC(y, m - 1, d, h, min, s, ms);
+	// Two passes so DST transitions near the boundary converge on the right offset
+	let ts = wallClockUtc;
+	for (let i = 0; i < 2; i++) {
+		ts = wallClockUtc - tzOffsetMs(timeZone, new Date(ts));
+	}
+	return new Date(ts).toISOString();
+}