first version

app/services/invoice/format.ts

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+/**
+ * Per-locale formatters used in PDF rendering. We pin these to specific
+ * locales (de-AT for German invoices) so that the output is deterministic
+ * regardless of the runtime's default locale.
+ */
+
+const MONEY_FORMATTERS = new Map<string, Intl.NumberFormat>();
+const QTY_FORMATTERS = new Map<string, Intl.NumberFormat>();
+const DATE_FORMATTERS = new Map<string, Intl.DateTimeFormat>();
+
+function localeFor(language: string): string {
+  return language === "en" ? "en-GB" : "de-AT";
+}
+
+export function formatMoney(
+  amount: number | string,
+  currency: string,
+  language: string,
+): string {
+  const num = typeof amount === "string" ? Number(amount) : amount;
+  const key = `${language}|${currency}`;
+  let f = MONEY_FORMATTERS.get(key);
+  if (!f) {
+    f = new Intl.NumberFormat(localeFor(language), {
+      style: "decimal",
+      minimumFractionDigits: 2,
+      maximumFractionDigits: 2,
+    });
+    MONEY_FORMATTERS.set(key, f);
+  }
+  return `${f.format(Number.isFinite(num) ? num : 0)} ${currency}`;
+}
+
+export function formatQuantity(qty: number, unit: string, language: string): string {
+  let f = QTY_FORMATTERS.get(language);
+  if (!f) {
+    f = new Intl.NumberFormat(localeFor(language), {
+      minimumFractionDigits: 2,
+      maximumFractionDigits: 2,
+    });
+    QTY_FORMATTERS.set(language, f);
+  }
+  return `${f.format(qty)} ${unit}`;
+}
+
+export function formatDate(date: Date | string, language: string): string {
+  const d = typeof date === "string" ? new Date(date) : date;
+  let f = DATE_FORMATTERS.get(language);
+  if (!f) {
+    f = new Intl.DateTimeFormat(localeFor(language), {
+      day: "2-digit",
+      month: "2-digit",
+      year: "numeric",
+    });
+    DATE_FORMATTERS.set(language, f);
+  }
+  return f.format(d);
+}
+
+/** Adds days to a date, returning a new Date. */
+export function addDays(date: Date, days: number): Date {
+  const d = new Date(date);
+  d.setDate(d.getDate() + days);
+  return d;
+}
+
+/**
+ * Formats a percentage. Tax rates from Shopify can be either 0.20 or 20 — we
+ * accept both shapes via heuristics.
+ */
+export function formatTaxRate(rate: number, language: string): string {
+  const pct = rate <= 1 ? rate * 100 : rate;
+  const f = new Intl.NumberFormat(localeFor(language), {
+    minimumFractionDigits: 0,
+    maximumFractionDigits: 2,
+  });
+  return `${f.format(pct)}%`;
+}