Stripe + E-Rechnung: So erzeugst du ZUGFeRD automatisch nach jeder Zahlung

// stripe-webhook.js — Stripe Webhook Handler
const express = require('express')
const Stripe = require('stripe')
const fetch = require('node-fetch')

const stripe = new Stripe(process.env.STRIPE_SECRET_KEY)
const app = express()

app.post('/webhook/stripe', express.raw({ type: 'application/json' }), async (req, res) => {
  const sig = req.headers['stripe-signature']
  let event

  try {
    event = stripe.webhooks.constructEvent(req.body, sig, process.env.STRIPE_WEBHOOK_SECRET)
  } catch (err) {
    return res.status(400).send(`Webhook Error: ${err.message}`)
  }

  if (event.type === 'invoice.paid') {
    const invoice = event.data.object
    const customer = await stripe.customers.retrieve(invoice.customer)

    // E-Rechnung via rechnungsapi.de erzeugen
    const response = await fetch('https://api.rechnungsapi.de/api/v1/zugferd/createZugferdFromJson', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${process.env.RECHNUNGSAPI_TOKEN}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        invoice: {
          invoiceNumber: invoice.number,
          invoiceIssueDate: new Date(invoice.created * 1000).toISOString().split('T')[0],
          invoiceTypeCode: '380',
          invoiceCurrencyCode: 'EUR',
          seller: {
            sellerName: 'Dein Unternehmen GmbH',
            sellerVatIdentifier: 'DE123456789',
            sellerElectronicAddress: 'rechnungen@deinunternehmen.de',
            sellerPostalAddress: {
              sellerAddressLine1: 'Musterstrasse 1',
              sellerCity: 'Berlin',
              sellerPostCode: '10115',
              sellerCountryCode: 'DE'
            }
          },
          buyer: {
            buyerName: customer.name,
            buyerElectronicAddress: customer.email,
            buyerPostalAddress: {
              buyerAddressLine1: customer.address?.line1 ?? '',
              buyerCity: customer.address?.city ?? '',
              buyerPostCode: customer.address?.postal_code ?? '',
              buyerCountryCode: customer.address?.country ?? 'DE'
            }
          },
          invoiceLine: invoice.lines.data.map((line, i) => ({
            invoiceLineIdentifier: String(i + 1),
            invoiceLineNetAmount: String((line.amount / 100).toFixed(2)),
            itemName: line.description,
            invoicedQuantity: String(line.quantity ?? 1),
            invoicedQuantityUnitOfMeasureCode: 'C62',
            itemNetPrice: String(((line.amount / 100) / (line.quantity ?? 1)).toFixed(2)),
            invoiceLineVatInformation: {
              invoiceLineVatCategoryCode: 'S',
              invoiceLineVatRate: 19
            }
          })),
          documentTotals: {
            sumOfInvoiceLineNetAmount: String((invoice.subtotal / 100).toFixed(2)),
            invoiceTotalAmountWithoutVat: String((invoice.subtotal / 100).toFixed(2)),
            invoiceTotalVatAmount: String((invoice.tax / 100).toFixed(2)),
            invoiceTotalAmountWithVat: String((invoice.total / 100).toFixed(2)),
            amountDueForPayment: String((invoice.amount_due / 100).toFixed(2))
          },
          vatBreakdown: [{
            vatCategoryTaxableAmount: String((invoice.subtotal / 100).toFixed(2)),
            vatCategoryTaxAmount: String((invoice.tax / 100).toFixed(2)),
            vatCategoryCode: 'S',
            vatCategoryRate: 19
          }]
        }
      })
    })

    const pdfBuffer = await response.buffer()
    // PDF per E-Mail versenden oder in S3/GDrive speichern
    console.log('ZUGFeRD-Rechnung erzeugt:', invoice.number)
  }

  res.json({ received: true })
})

app.listen(3000, () => console.log('Webhook server running on port 3000'))