ADD: changed to rect router

app/lib/invoice-number.ts

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+import prisma from "./prisma";
+
+export async function generateInvoiceNumber(companyId: string): Promise<string> {
+  const year = new Date().getFullYear();
+
+  const company = await prisma.company.update({
+    where: { id: companyId },
+    data: { invoiceSequence: { increment: 1 } },
+    select: { invoicePrefix: true, invoiceSequence: true },
+  });
+
+  const seq = String(company.invoiceSequence).padStart(3, "0");
+  return `${company.invoicePrefix}-${year}-${seq}`;
+}

app/lib/prisma.ts

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+import { PrismaClient } from "@prisma/client";
+
+const globalForPrisma = globalThis as unknown as {
+  prisma: PrismaClient | undefined;
+};
+
+export const prisma = globalForPrisma.prisma ?? new PrismaClient();
+
+if (process.env.NODE_ENV !== "production") globalForPrisma.prisma = prisma;
+
+export default prisma;

app/lib/tax.ts

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+export const TAX_RATES = [
+  { label: "19% MwSt. (Regelsteuersatz)", value: 19 },
+  { label: "7% MwSt. (ermäßigt)", value: 7 },
+  { label: "0% (steuerfrei / §13b UStG)", value: 0 },
+] as const;
+
+export function calcItemAmounts(
+  quantity: number,
+  unitPrice: number,
+  taxRate: number
+) {
+  const netAmount = Math.round(quantity * unitPrice * 100) / 100;
+  const taxAmount = Math.round(netAmount * (taxRate / 100) * 100) / 100;
+  const grossAmount = Math.round((netAmount + taxAmount) * 100) / 100;
+  return { netAmount, taxAmount, grossAmount };
+}
+
+export function calcInvoiceTotals(
+  items: Array<{ netAmount: number; taxAmount: number; grossAmount: number }>
+) {
+  const netTotal = items.reduce((sum, i) => sum + i.netAmount, 0);
+  const taxTotal = items.reduce((sum, i) => sum + i.taxAmount, 0);
+  const grossTotal = items.reduce((sum, i) => sum + i.grossAmount, 0);
+  return {
+    netTotal: Math.round(netTotal * 100) / 100,
+    taxTotal: Math.round(taxTotal * 100) / 100,
+    grossTotal: Math.round(grossTotal * 100) / 100,
+  };
+}
+
+export function formatCurrency(amount: number | string): string {
+  return new Intl.NumberFormat("de-DE", {
+    style: "currency",
+    currency: "EUR",
+  }).format(Number(amount));
+}
+
+export function formatDate(date: Date | string): string {
+  return new Intl.DateTimeFormat("de-DE").format(new Date(date));
+}

app/lib/utils.ts

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+import { type ClassValue, clsx } from "clsx";
+import { twMerge } from "tailwind-merge";
+
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs));
+}