Branded transactional receipts & licensing for Polar.sh merchant of record and micro-SaaS sales

// app/api/webhooks/polar/route.ts
// Listen to Polar.sh order.created events to send branded React Email receipts
import { Webhook } from 'svix';
import { headers } from 'next/headers';
import { SadaSend } from 'sadasend';

const sadasend = new SadaSend({ apiKey: process.env.SADASEND_API_KEY! });

export async function POST(req: Request) {
  const headerPayload = await headers();
  const svixId = headerPayload.get('webhook-id') || headerPayload.get('svix-id');
  const svixTimestamp = headerPayload.get('webhook-timestamp') || headerPayload.get('svix-timestamp');
  const svixSignature = headerPayload.get('webhook-signature') || headerPayload.get('svix-signature');

  const payload = await req.json();
  const body = JSON.stringify(payload);
  const wh = new Webhook(process.env.POLAR_WEBHOOK_SECRET!);

  let evt: { type: string; data: { customer: { email: string; name?: string }; product: { name: string }; amount: number; currency: string } };
  try {
    evt = wh.verify(body, {
      'svix-id': svixId!,
      'svix-timestamp': svixTimestamp!,
      'svix-signature': svixSignature!,
    }) as typeof evt;
  } catch {
    return new Response('Invalid webhook signature', { status: 400 });
  }

  if (evt.type === 'order.created') {
    const { customer, product, amount, currency } = evt.data;
    const formattedPrice = (amount / 100).toFixed(2);

    await sadasend.emails.send({
      from: 'billing@yourdomain.com',
      to: customer.email,
      subject: `Receipt for your purchase of ${product.name}`,
      html: `<p>Hi ${customer.name || 'there'},</p>
             <p>Thank you for purchasing <strong>${product.name}</strong>!</p>
             <p>Total Paid: ${formattedPrice} ${currency.toUpperCase()}</p>
             <p>Your license key and onboarding access are now active.</p>`,
      verifyBeforeSend: true,
    });
  }

  return new Response('OK', { status: 200 });
}