init

src/lib/time.ts

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+/**
+ * Human time helpers for the alarm surfaces.
+ *
+ * The takeover shows a count-up ("2s ago") rather than a server timestamp: on a
+ * lock screen at arm's length an RFC3339 string is unreadable, and the number
+ * that matters is how long the phone has been screaming. The absolute time is
+ * still available as the accessibility label.
+ */
+
+/** Parse a server RFC3339 string. Returns null when absent or unparseable. */
+export function parseServerTime(value: string | null | undefined): Date | null {
+  if (!value) return null;
+  const ms = Date.parse(value);
+  return Number.isNaN(ms) ? null : new Date(ms);
+}
+
+const SECOND = 1000;
+const MINUTE = 60 * SECOND;
+const HOUR = 60 * MINUTE;
+const DAY = 24 * HOUR;
+
+/**
+ * Compact elapsed time. Deliberately coarse above a minute: the takeover updates
+ * every second only while the alarm is fresh, and "13m ago" is more useful than
+ * "13m 42s ago" on a wall of red.
+ */
+export function relativeTime(from: Date, now: number): string {
+  const elapsed = now - from.getTime();
+  // A clock skew between phone and server must not render "in 3 seconds".
+  if (elapsed < SECOND) return 'just now';
+  if (elapsed < MINUTE) return `${Math.floor(elapsed / SECOND)}s ago`;
+  if (elapsed < HOUR) return `${Math.floor(elapsed / MINUTE)}m ago`;
+  if (elapsed < DAY) return `${Math.floor(elapsed / HOUR)}h ago`;
+  return `${Math.floor(elapsed / DAY)}d ago`;
+}
+
+/** Convenience: relative time for a server string, or null when unparseable. */
+export function relativeSince(value: string | null | undefined, now: number): string | null {
+  const date = parseServerTime(value);
+  return date ? relativeTime(date, now) : null;
+}
+
+/** Local wall-clock time for the accessibility label of a relative stamp. */
+export function absoluteLocal(date: Date): string {
+  const hh = String(date.getHours()).padStart(2, '0');
+  const mm = String(date.getMinutes()).padStart(2, '0');
+  const ss = String(date.getSeconds()).padStart(2, '0');
+  return `${hh}:${mm}:${ss}`;
+}