refactor: move shared utilities to lib/shared/ sub-packages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/shared/utils/date.ts

@@ -0,0 +1,123 @@
+/**
+ * Format an ISO date string (YYYY-MM-DD) for display.
+ * Uses T12:00:00 to avoid UTC timezone off-by-one when converting to local time.
+ * Defaults to 'long' (e.g. "24. Dezember 1943"); pass 'short' for DD.MM.YYYY.
+ */
+export function formatDate(isoDate: string, format: 'short' | 'long' = 'long'): string {
+	const date = new Date(isoDate + 'T12:00:00');
+	if (format === 'short') {
+		return new Intl.DateTimeFormat('de-DE', {
+			day: '2-digit',
+			month: '2-digit',
+			year: 'numeric'
+		}).format(date);
+	}
+	return new Intl.DateTimeFormat('de-DE', {
+		day: 'numeric',
+		month: 'long',
+		year: 'numeric'
+	}).format(date);
+}
+
+/**
+ * Format an ISO date string for medium-length display (e.g. "15. Jun. 1920").
+ * Uses T12:00:00 to avoid UTC timezone off-by-one.
+ * Pass an explicit BCP 47 locale tag to respect the app locale; defaults to 'de-DE'.
+ */
+export function formatMCDate(isoDate: string, locale: string = 'de-DE'): string {
+	return new Intl.DateTimeFormat(locale, {
+		day: 'numeric',
+		month: 'short',
+		year: 'numeric'
+	}).format(new Date(isoDate + 'T12:00:00'));
+}
+
+/**
+ * Converts an ISO date string (YYYY-MM-DD) to German display format (DD.MM.YYYY).
+ * Returns an empty string for invalid or empty input.
+ */
+export function isoToGerman(iso: string): string {
+	if (!iso || !/^\d{4}-\d{2}-\d{2}$/.test(iso)) return '';
+	const [y, m, d] = iso.split('-');
+	return `${d}.${m}.${y}`;
+}
+
+/**
+ * Converts a German date string (DD.MM.YYYY) to ISO format (YYYY-MM-DD).
+ * Returns an empty string for invalid or empty input.
+ */
+export function germanToIso(german: string): string {
+	const match = german.match(/^(\d{2})\.(\d{2})\.(\d{4})$/);
+	if (!match) return '';
+	const [, d, m, y] = match;
+	return `${y}-${m}-${d}`;
+}
+
+/**
+ * Formats a raw date string into German DD.MM.YYYY format.
+ *
+ * Handles two modes:
+ * - Pure digit stream (no dots): auto-inserts dots after position 2 and 4
+ * - Manual dot entry: preserves user-typed dots, pads single-digit day/month,
+ *   and overflows extra digits from day→month and month→year
+ */
+export function formatGermanDateInput(raw: string): string {
+	if (!raw.includes('.')) {
+		const digits = raw.replace(/\D/g, '').slice(0, 8);
+		if (digits.length <= 2) return digits;
+		if (digits.length <= 4) return `${digits.slice(0, 2)}.${digits.slice(2)}`;
+		return `${digits.slice(0, 2)}.${digits.slice(2, 4)}.${digits.slice(4)}`;
+	}
+
+	const trailingDot = raw.endsWith('.');
+	const parts = raw.split('.').map((p) => p.replace(/\D/g, ''));
+
+	let day = parts[0] ?? '';
+	let month = parts[1] ?? '';
+	let year = parts[2] ?? '';
+
+	let dayOverflowed = false;
+	if (day.length > 2) {
+		month = day.slice(2) + month;
+		day = day.slice(0, 2);
+		dayOverflowed = true;
+	}
+
+	let monthOverflowed = false;
+	if (month.length > 2) {
+		year = month.slice(2) + year;
+		month = month.slice(0, 2);
+		monthOverflowed = true;
+	}
+
+	year = year.slice(0, 4);
+
+	const afterDay = !dayOverflowed && parts.length >= 2;
+
+	if (day.length === 1 && (month || (trailingDot && !dayOverflowed))) {
+		day = '0' + day;
+	}
+	if (month.length === 1 && (year || (trailingDot && afterDay && !monthOverflowed))) {
+		month = '0' + month;
+	}
+
+	if (year) return `${day}.${month}.${year}`;
+	if (month) {
+		const dot2 = trailingDot && afterDay && !monthOverflowed ? '.' : '';
+		return `${day}.${month}${dot2}`;
+	}
+	const dot1 = trailingDot && !dayOverflowed ? '.' : '';
+	return `${day}${dot1}`;
+}
+
+/**
+ * Handles a date input event for German-format date fields (DD.MM.YYYY).
+ * Strips non-digits, formats with dots, mutates the input's displayed value,
+ * and returns the display string and its ISO equivalent.
+ */
+export function handleGermanDateInput(e: Event): { display: string; iso: string } {
+	const input = e.target as HTMLInputElement;
+	const display = formatGermanDateInput(input.value);
+	input.value = display;
+	return { display, iso: germanToIso(display) };
+}