Phase 0.3: migrate date formatting to date-fns

frontend/src/utils/date.ts

@@ -0,0 +1,86 @@
+import { format, formatDistanceToNow, parseISO, isValid, isToday } from 'date-fns';
+import { de } from 'date-fns/locale';
+
+/**
+ * Parse a date string or Date object into a valid Date, or null if invalid/empty.
+ */
+function toDate(value: string | Date | null | undefined): Date | null {
+  if (value === null || value === undefined || value === '') return null;
+  if (value instanceof Date) return isValid(value) ? value : null;
+  const parsed = parseISO(value);
+  return isValid(parsed) ? parsed : null;
+}
+
+/**
+ * Format a date with a custom date-fns pattern and German locale.
+ * Returns empty string for null/undefined/invalid dates.
+ */
+export function formatDate(date: string | Date | null | undefined, pattern: string): string {
+  const d = toDate(date);
+  if (!d) return '';
+  return format(d, pattern, { locale: de });
+}
+
+/**
+ * Standard date + time format: dd.MM.yyyy HH:mm
+ */
+export function formatDateTime(date: string | Date | null | undefined): string {
+  return formatDate(date, 'dd.MM.yyyy HH:mm');
+}
+
+/**
+ * Short date format: dd.MM.yyyy
+ */
+export function formatDateShort(date: string | Date | null | undefined): string {
+  return formatDate(date, 'dd.MM.yyyy');
+}
+
+/**
+ * Time only format: HH:mm
+ */
+export function formatTime(date: string | Date | null | undefined): string {
+  return formatDate(date, 'HH:mm');
+}
+
+/**
+ * Relative time format: "vor 5 Minuten", "in 2 Stunden"
+ */
+export function formatRelative(date: string | Date | null | undefined): string {
+  const d = toDate(date);
+  if (!d) return '';
+  return formatDistanceToNow(d, { locale: de, addSuffix: true });
+}
+
+/**
+ * Month + day format: "15. Juli"
+ */
+export function formatMonthDay(date: string | Date | null | undefined): string {
+  return formatDate(date, 'd. MMMM');
+}
+
+/**
+ * Smart date: shows time (HH:mm) if today, otherwise short date (d. MMM).
+ * Used in mail list and similar compact views.
+ */
+export function formatSmartDate(date: string | Date | null | undefined): string {
+  const d = toDate(date);
+  if (!d) return '';
+  if (isToday(d)) {
+    return format(d, 'HH:mm', { locale: de });
+  }
+  return format(d, 'd. MMM', { locale: de });
+}
+
+/**
+ * Date input format for <input type="date">: yyyy-MM-dd
+ */
+export function formatDateInput(date: string | Date | null | undefined): string {
+  return formatDate(date, 'yyyy-MM-dd');
+}
+
+/**
+ * DateTime input format for <input type="datetime-local">: yyyy-MM-ddTHH:mm
+ */
+export function formatDateTimeInput(date: string | Date | null | undefined): string {
+  return formatDate(date, "yyyy-MM-dd'T'HH:mm");
+}