Task e0a2b862: Today tab (#192)

2026-09-23 20:13:52 -04:00
parent 4ff40f00a2
commit be4fd04754
10 changed files with 1030 additions and 12 deletions
@@ -0,0 +1,50 @@
+/**
+ * Date/time formatting for the Today tab.
+ *
+ * Calendar dates ("YYYY-MM-DD") are parsed by their components and formatted
+ * in UTC, so the printed day never shifts with the viewer's offset — unlike
+ * `new Date("YYYY-MM-DD")`, which is UTC midnight and reads as the previous
+ * day in negative-offset zones.
+ */
+
+const LOCALE = "en-US";
+
+function calendarDate(iso: string): Date {
+  const match = /^(\d{4})-(\d{2})-(\d{2})$/.exec(iso);
+  if (!match) throw new Error(`Invalid calendar date: ${iso}`);
+  const [, year, month, day] = match;
+  return new Date(Date.UTC(Number(year), Number(month) - 1, Number(day)));
+}
+
+function format(date: Date, options: Intl.DateTimeFormatOptions): string {
+  // Newer ICU puts a narrow no-break space before AM/PM; normalise it.
+  return new Intl.DateTimeFormat(LOCALE, options)
+    .format(date)
+    .replace(/ /g, " ");
+}
+
+/** "Wednesday, September 23" */
+export function formatLongDate(iso: string): string {
+  const date = calendarDate(iso);
+  const weekday = format(date, { weekday: "long", timeZone: "UTC" });
+  const monthDay = format(date, { month: "long", day: "numeric", timeZone: "UTC" });
+  return `${weekday}, ${monthDay}`;
+}
+
+/** "Sep 23" */
+export function formatShortDate(iso: string): string {
+  return format(calendarDate(iso), { month: "short", day: "numeric", timeZone: "UTC" });
+}
+
+/** "09:00" -> "9:00 AM" (a wall-clock time, no zone conversion). */
+export function formatDueTime(hhmm: string): string {
+  const match = /^(\d{2}):(\d{2})/.exec(hhmm);
+  if (!match) return hhmm;
+  const date = new Date(Date.UTC(2000, 0, 1, Number(match[1]), Number(match[2])));
+  return format(date, { hour: "numeric", minute: "2-digit", timeZone: "UTC" });
+}
+
+/** A UTC ISO timestamp shown as the viewer's local time, "7:04 AM". */
+export function formatClockTime(isoTimestamp: string): string {
+  return format(new Date(isoTimestamp), { hour: "numeric", minute: "2-digit" });
+}