admin: fix timestamps, per-day stats, reset, delete drinks/bars

- store created_at as UTC ISO; display/group in Europe/Berlin
- stats grouped by business day (sales night past midnight, 5am cutoff)
- add "Statistik zurücksetzen"
- allow deleting drinks/tresen (refused if referenced by sales)
- CSV exports local wall-clock time

server/src/time.ts

@@ -0,0 +1,78 @@
+// Time handling for the sales day.
+//
+// Timestamps are stored in the DB as UTC ISO strings (`new Date().toISOString()`).
+// For display and for grouping into business days we convert to a fixed local
+// timezone (default Europe/Berlin) so the numbers match the bar's wall clock
+// regardless of where the server runs.
+
+export const TZ = process.env.WUTZ_TZ ?? 'Europe/Berlin';
+
+// A sale at e.g. 03:00 still belongs to the previous night's business day.
+// Anything before this local hour counts towards the day before.
+export const BUSINESS_DAY_CUTOFF_HOUR = Number(process.env.WUTZ_DAY_CUTOFF_HOUR ?? 5);
+
+/**
+ * Parse a value stored in `created_at`. New rows are UTC ISO strings (with `Z`),
+ * but legacy rows written by SQLite's CURRENT_TIMESTAMP look like
+ * `YYYY-MM-DD HH:MM:SS` and are also UTC — normalise both to a Date.
+ */
+export function parseDbTime(s: string): Date {
+  if (/[zZ]|[+-]\d{2}:\d{2}$/.test(s)) return new Date(s);
+  return new Date(s.replace(' ', 'T') + 'Z');
+}
+
+interface LocalParts {
+  year: number;
+  month: number;
+  day: number;
+  hour: number;
+  minute: number;
+  second: number;
+}
+
+function localParts(d: Date, tz: string = TZ): LocalParts {
+  const fmt = new Intl.DateTimeFormat('en-CA', {
+    timeZone: tz,
+    year: 'numeric',
+    month: '2-digit',
+    day: '2-digit',
+    hour: '2-digit',
+    minute: '2-digit',
+    second: '2-digit',
+    hour12: false,
+  });
+  const parts: Record<string, string> = {};
+  for (const p of fmt.formatToParts(d)) {
+    if (p.type !== 'literal') parts[p.type] = p.value;
+  }
+  return {
+    year: Number(parts.year),
+    month: Number(parts.month),
+    day: Number(parts.day),
+    hour: Number(parts.hour === '24' ? '0' : parts.hour),
+    minute: Number(parts.minute),
+    second: Number(parts.second),
+  };
+}
+
+/** Local wall-clock time as `YYYY-MM-DD HH:MM:SS` for CSV / display. */
+export function formatLocal(d: Date, tz: string = TZ): string {
+  const p = localParts(d, tz);
+  const pad = (n: number) => String(n).padStart(2, '0');
+  return `${p.year}-${pad(p.month)}-${pad(p.day)} ${pad(p.hour)}:${pad(p.minute)}:${pad(p.second)}`;
+}
+
+/**
+ * The business day a timestamp belongs to, as `YYYY-MM-DD`.
+ * Hours before BUSINESS_DAY_CUTOFF_HOUR are attributed to the previous day.
+ */
+export function businessDay(d: Date, tz: string = TZ): string {
+  const p = localParts(d, tz);
+  // Build a date from the local Y-M-D and roll back a day when before cutoff.
+  const date = new Date(Date.UTC(p.year, p.month - 1, p.day));
+  if (p.hour < BUSINESS_DAY_CUTOFF_HOUR) {
+    date.setUTCDate(date.getUTCDate() - 1);
+  }
+  const pad = (n: number) => String(n).padStart(2, '0');
+  return `${date.getUTCFullYear()}-${pad(date.getUTCMonth() + 1)}-${pad(date.getUTCDate())}`;
+}