How to generate and download a Factur-X invoice

const BASE_URL = "https://thirdparty.qonto.com/v2";
const headers = {
  Authorization: "Bearer {your_access_token}",
  "Content-Type": "application/json",
};

// Option A: Find an existing client
const searchResponse = await fetch(
  `${BASE_URL}/clients?${new URLSearchParams({ "filter[email]": "contact@acmecorp.com" })}`,
  { headers }
);
const { clients } = await searchResponse.json();

let clientId;
if (clients.length > 0) {
  clientId = clients[0].id;
  console.log(`Found existing client: ${clientId}`);
} else {
  // Option B: Create a new client
  const createResponse = await fetch(`${BASE_URL}/clients`, {
    method: "POST",
    headers,
    body: JSON.stringify({
      name: "Acme Corp",
      kind: "company",
      email: "contact@acmecorp.com",
      currency: "EUR",  // Required
      locale: "en",     // Required
      tax_identification_number: "123456789", // Required for creating client invoices
      billing_address: {
        street_address: "1 Market Street",
        city: "Paris",
        zip_code: "75001",
        country_code: "FR",
      },
    }),
  });
  const { client } = await createResponse.json();
  clientId = client.id;
  console.log(`Created new client: ${clientId}`);
}

const orgResponse = await fetch(`${BASE_URL}/organization`, { headers });
if (!orgResponse.ok) throw new Error(`HTTP ${orgResponse.status}`);

const { organization } = await orgResponse.json();
// Use the first account, or filter by slug/currency as needed
const receivingIban = organization.bank_accounts[0].iban;
console.log(`Receiving IBAN: ${receivingIban}`);

const today = new Date().toISOString().split("T")[0];
const dueDate = new Date(Date.now() + 30 * 86400000).toISOString().split("T")[0];

const invoiceResponse = await fetch(`${BASE_URL}/client_invoices`, {
  method: "POST",
  headers,
  body: JSON.stringify({
    client_id: clientId,
    issue_date: today,
    due_date: dueDate,
    status: "draft",
    payment_methods: {
      iban: receivingIban,
    },
    items: [
      {
        title: "Consulting Services — March 2026",
        quantity: "10",
        unit: "hour",
        unit_price: { value: "150.00", currency: "EUR" },
        vat_rate: "0.20",
      },
    ],
  }),
});
if (!invoiceResponse.ok) throw new Error(`HTTP ${invoiceResponse.status}`);

const { client_invoice: invoice } = await invoiceResponse.json();
const invoiceId = invoice.id;
console.log(`Invoice draft created: ${invoiceId}`);

const finalizeResponse = await fetch(
  `${BASE_URL}/client_invoices/${invoiceId}/finalize`,
  { method: "POST", headers }
);
if (!finalizeResponse.ok) throw new Error(`HTTP ${finalizeResponse.status}`);

const { client_invoice: finalizedInvoice } = await finalizeResponse.json();
let attachmentId = finalizedInvoice.attachment_id ?? null; // May be null initially
const finalizedAt = finalizedInvoice.finalized_at;
console.log(`Invoice finalized at ${finalizedAt} — attachment: ${attachmentId}`);

const MAX_ATTEMPTS = 15;
const POLL_INTERVAL_MS = 2000;

let attachment;

for (let attempt = 0; attempt < MAX_ATTEMPTS; attempt++) {
  // attachment_id may not be set immediately — re-fetch the invoice if needed
  if (!attachmentId) {
    const invoiceResponse = await fetch(
      `${BASE_URL}/client_invoices/${invoiceId}`,
      { headers }
    );
    if (!invoiceResponse.ok) throw new Error(`HTTP ${invoiceResponse.status}`);
    const { client_invoice } = await invoiceResponse.json();
    attachmentId = client_invoice.attachment_id ?? null;
    if (!attachmentId) {
      console.log(`Attempt ${attempt + 1}/${MAX_ATTEMPTS} — attachment_id not set yet, waiting...`);
      await new Promise((resolve) => setTimeout(resolve, POLL_INTERVAL_MS));
      continue;
    }
  }

  const attachmentResponse = await fetch(
    `${BASE_URL}/attachments/${attachmentId}`,
    { headers }
  );
  if (!attachmentResponse.ok) throw new Error(`HTTP ${attachmentResponse.status}`);

  attachment = (await attachmentResponse.json()).attachment;
  console.log("Factur-X PDF is ready!");
  break;
}

if (!attachment) {
  throw new Error("Factur-X PDF was not ready within the timeout period.");
}

import { writeFile, mkdir } from "node:fs/promises";

const fileResponse = await fetch(attachment.url);
if (!fileResponse.ok) throw new Error(`Download failed: ${fileResponse.status}`);

await mkdir("./client_invoices", { recursive: true });
const buffer = Buffer.from(await fileResponse.arrayBuffer());
const filePath = `./client_invoices/${attachment.file_name}`;
await writeFile(filePath, buffer);

console.log(`Downloaded Factur-X PDF: ${filePath}`);