feat(invoice): Rechnungen als E-Rechnung (ZUGFeRD/Factur-X EN 16931)

Jedes Rechnungs-PDF ist jetzt eine hybride E-Rechnung: PDF/A-3b mit
eingebettetem factur-x.xml (CII D16B, Profil EN 16931). Netto und Steuer je
Satz kommen unveraendert aus der Aufstellung des PDFs, Versand und Rabatt
stehen als Zu- und Abschlag je Satz; XML und PDF tragen dieselben Summen.

- lib/einvoice/cii.ts: XML-Erzeugung (Rechnung 380, Stornorechnung 381 mit
  Bezug), ohne USt-IdNr. oder bei Positionen ohne Satz nur PDF mit Warnung
- lib/einvoice/facturx-pdf.ts: PDF/A-3b, Factur-X-XMP mit Erweiterungsschema,
  eingebettete Liberation-Schriften (gleiche Laufweiten wie Helvetica/Times)
- invoice-pdf: Darstellung als Stornorechnung (negative Betraege, Bezug)
- Geprueft mit XSD, CEN-Schematron EN 16931 1.3.16 und Mustang 2.26
  (veraPDF: PDF/A-3b konform, XML valid)

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

Dockerfile

@@ -67,6 +67,7 @@ COPY --from=builder --chown=nextjs:nodejs /app/node_modules ./node_modules
 COPY --from=builder --chown=nextjs:nodejs /app/src ./src
 COPY --from=builder --chown=nextjs:nodejs /app/scripts ./scripts
 COPY --from=builder --chown=nextjs:nodejs /app/prisma ./prisma
+COPY --from=builder --chown=nextjs:nodejs /app/assets ./assets
 COPY --from=builder --chown=nextjs:nodejs /app/prisma.config.ts /app/package.json /app/tsconfig.json ./
 ENV PATH="/app/node_modules/.bin:${PATH}"
 USER 1001
@@ -87,6 +88,9 @@ RUN addgroup --system --gid 1001 nodejs \
   && adduser --system --uid 1001 nextjs
 
 COPY --from=builder /app/public ./public
+# Eingebettete Schriften der Rechnungs-PDFs (PDF/A-3, lib/einvoice/facturx-pdf.ts
+# liest sie zur Laufzeit aus process.cwd()/assets/fonts).
+COPY --from=builder /app/assets ./assets
 COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
 COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
 COPY --from=builder /app/prisma ./prisma

assets/fonts/LICENSE-Liberation.txt

@@ -0,0 +1,102 @@
+Digitized data copyright (c) 2010 Google Corporation
+	with Reserved Font Arimo, Tinos and Cousine.
+Copyright (c) 2012 Red Hat, Inc.
+	with Reserved Font Name Liberation.
+
+This Font Software is licensed under the SIL Open Font License,
+Version 1.1.
+
+This license is copied below, and is also available with a FAQ at:
+http://scripts.sil.org/OFL
+
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+
+PREAMBLE The goals of the Open Font License (OFL) are to stimulate
+worldwide development of collaborative font projects, to support the font
+creation efforts of academic and linguistic communities, and to provide
+a free and open framework in which fonts may be shared and improved in
+partnership with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves.
+The fonts, including any derivative works, can be bundled, embedded,
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works.  The fonts and derivatives,
+however, cannot be released under any other type of license.  The
+requirement for fonts to remain under this license does not apply to
+any document created using the fonts or their derivatives.
+
+ 
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such.
+This may include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components
+as distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting ? in part or in whole ?
+any of the components of the Original Version, by changing formats or
+by porting the Font Software to a new environment.
+
+"Author" refers to any designer, engineer, programmer, technical writer
+or other person who contributed to the Font Software.
+
+
+PERMISSION & CONDITIONS
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of the Font Software, to use, study, copy, merge, embed, modify,
+redistribute, and sell modified and unmodified copies of the Font
+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,in
+   Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+   redistributed and/or sold with any software, provided that each copy
+   contains the above copyright notice and this license. These can be
+   included either as stand-alone text files, human-readable headers or
+   in the appropriate machine-readable metadata fields within text or
+   binary files as long as those fields can be easily viewed by the user.
+
+3) No Modified Version of the Font Software may use the Reserved Font
+   Name(s) unless explicit written permission is granted by the
+   corresponding Copyright Holder. This restriction only applies to the
+   primary font name as presented to the users.
+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+   Software shall not be used to promote, endorse or advertise any
+   Modified Version, except to acknowledge the contribution(s) of the
+   Copyright Holder(s) and the Author(s) or with their explicit written
+   permission.
+
+5) The Font Software, modified or unmodified, in part or in whole, must
+   be distributed entirely under this license, and must not be distributed
+   under any other license. The requirement for fonts to remain under
+   this license does not apply to any document created using the Font
+   Software.
+
+
+ 
+TERMINATION
+This license becomes null and void if any of the above conditions are not met.
+
+ 
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
+OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT.  IN NO EVENT SHALL THE
+COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
+DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM OTHER
+DEALINGS IN THE FONT SOFTWARE.
+

src/i18n/dictionaries/de.ts

@@ -1652,6 +1652,12 @@ export const de: Dictionary = {
     thankYou: "Vielen Dank, dass du unsere Imkerei unterstützt!",
     pageLabel: (page, total) => `Seite ${page} von ${total}`,
     legalNote: "Diese Rechnung wurde automatisch erzeugt und ist ohne Unterschrift gültig.",
+    cancellationTitle: "Stornorechnung",
+    cancellationNumberLabel: "Stornorechnungsnr.",
+    cancellationDateLabel: "Datum",
+    cancelsInvoiceLabel: "Zur Rechnung",
+    cancellationNote: (invoiceNumber, invoiceDate) =>
+      `Diese Stornorechnung hebt die Rechnung ${invoiceNumber} vom ${invoiceDate} vollständig auf. Der Betrag wird über die ursprüngliche Zahlungsart erstattet.`,
   },
   addressesPage: {
     title: "Meine Adressen",

src/i18n/dictionaries/en.ts

@@ -1626,6 +1626,12 @@ export const en: Dictionary = {
     thankYou: "Thank you for supporting our apiary!",
     pageLabel: (page, total) => `Page ${page} of ${total}`,
     legalNote: "This invoice was generated automatically and is valid without a signature.",
+    cancellationTitle: "Cancellation invoice",
+    cancellationNumberLabel: "Cancellation no.",
+    cancellationDateLabel: "Date",
+    cancelsInvoiceLabel: "Cancels invoice",
+    cancellationNote: (invoiceNumber, invoiceDate) =>
+      `This cancellation invoice fully reverses invoice ${invoiceNumber} dated ${invoiceDate}. The amount will be refunded via the original payment method.`,
   },
   addressesPage: {
     title: "My Addresses",

src/i18n/dictionary-type.ts

@@ -1169,6 +1169,11 @@ export interface Dictionary {
     thankYou: string;
     pageLabel: (page: number, total: number) => string;
     legalNote: string;
+    cancellationTitle: string;
+    cancellationNumberLabel: string;
+    cancellationDateLabel: string;
+    cancelsInvoiceLabel: string;
+    cancellationNote: (invoiceNumber: string, invoiceDate: string) => string;
   };
   addressesPage: {
     title: string;

src/lib/einvoice/cii.test.ts

@@ -0,0 +1,171 @@
+import { describe, test, expect } from "vitest";
+import { amount, buildCiiXml, escapeXml, type EInvoiceInput } from "./cii";
+import { vatBreakdown } from "@/lib/vat";
+
+function input(overrides: Partial<EInvoiceInput> = {}): EInvoiceInput {
+  const items = [
+    { name: "Waldhonig 500 g", quantity: 3, totalCents: 2697, vatRatePercent: 7 },
+    { name: "Bienenwachskerze", quantity: 1, totalCents: 1290, vatRatePercent: 19 },
+    { name: "Blütenhonig 250 g", quantity: 2, totalCents: 1198, vatRatePercent: 7 },
+  ];
+  return {
+    kind: "invoice",
+    number: "RE-2026-0042",
+    issuedAt: new Date(2026, 9, 12, 10, 0),
+    currency: "EUR",
+    orderNumber: "WH-2026-0042",
+    seller: {
+      name: "Wabenhain",
+      street: "Musterweg 1",
+      zip: "12345",
+      city: "Musterstadt",
+      countryCode: "DE",
+      vatId: "DE123456789",
+      email: "[email protected]",
+    },
+    buyer: { name: "Erika Musterfrau", street: "Musterstraße 1", zip: "80331", city: "München", countryCode: "DE" },
+    items,
+    shippingCents: 490,
+    discountCents: 300,
+    discountCode: "SOMMER",
+    totalCents: 2697 + 1290 + 1198 + 490 - 300,
+    paymentNote: "Bereits bezahlt (Online-Zahlung über Stripe).",
+    ...overrides,
+  };
+}
+
+function values(xml: string, element: string): string[] {
+  return [...xml.matchAll(new RegExp(`<${element}[^>]*>([^<]*)</${element}>`, "g"))].map((match) => match[1]);
+}
+
+function cents(value: string): number {
+  return Math.round(Number(value) * 100);
+}
+
+function single(xml: string, element: string): number {
+  const found = values(xml, element);
+  expect(found).toHaveLength(1);
+  return cents(found[0]);
+}
+
+function headerLineTotal(xml: string): number {
+  const match = /<ram:SpecifiedTradeSettlementHeaderMonetarySummation><ram:LineTotalAmount>([^<]*)</.exec(xml);
+  if (!match) throw new Error("BT-106 fehlt");
+  return cents(match[1]);
+}
+
+function ok(data: EInvoiceInput): string {
+  const result = buildCiiXml(data);
+  if (!result.ok) throw new Error(result.reason);
+  return result.xml;
+}
+
+describe("buildCiiXml", () => {
+  test("Summen stimmen mit der Steueraufstellung des PDFs auf den Cent ueberein", () => {
+    // Arrange
+    const data = input();
+    const rated = data.items.map((item) => ({ totalCents: item.totalCents, vatRatePercent: item.vatRatePercent ?? 0 }));
+    const expected = vatBreakdown({ items: rated, shippingCents: 490, discountCents: 300 });
+
+    // Act
+    const xml = ok(data);
+
+    // Assert
+    expect(values(xml, "ram:BasisAmount").map(cents)).toEqual(expected.map((line) => line.netCents));
+    expect(values(xml, "ram:CalculatedAmount").map(cents)).toEqual(expected.map((line) => line.vatCents));
+    const basis = single(xml, "ram:TaxBasisTotalAmount");
+    const tax = single(xml, "ram:TaxTotalAmount");
+    expect(headerLineTotal(xml) - single(xml, "ram:AllowanceTotalAmount") + single(xml, "ram:ChargeTotalAmount")).toBe(basis);
+    expect(basis + tax).toBe(data.totalCents);
+    expect(single(xml, "ram:GrandTotalAmount")).toBe(data.totalCents);
+    expect(single(xml, "ram:TotalPrepaidAmount")).toBe(data.totalCents);
+    expect(single(xml, "ram:DuePayableAmount")).toBe(0);
+  });
+
+  test("Positionen ergeben zusammen genau die Positionssumme (BT-106)", () => {
+    // Act
+    const xml = ok(input());
+
+    // Assert
+    const lineAmounts = [
+      ...xml.matchAll(/<ram:SpecifiedTradeSettlementLineMonetarySummation><ram:LineTotalAmount>([^<]*)</g),
+    ].map((match) => cents(match[1]));
+    expect(lineAmounts).toHaveLength(3);
+    expect(lineAmounts.reduce((sum, value) => sum + value, 0)).toBe(headerLineTotal(xml));
+    expect(values(xml, "ram:BilledQuantity")).toEqual(["3", "2", "1"]);
+  });
+
+  test("Kopfdaten: Profil EN 16931, Typ 380, Datum, Verkaeufer mit USt-IdNr.", () => {
+    // Act
+    const xml = ok(input());
+
+    // Assert
+    expect(xml).toContain("<ram:ID>urn:cen.eu:en16931:2017</ram:ID>");
+    expect(xml).toContain("<ram:TypeCode>380</ram:TypeCode>");
+    expect(xml).toContain('<udt:DateTimeString format="102">20261012</udt:DateTimeString>');
+    expect(xml).toContain('<ram:ID schemeID="VA">DE123456789</ram:ID>');
+    expect(xml).toContain("<ram:Reason>Rabatt (SOMMER)</ram:Reason>");
+    expect(xml).toContain("<ram:Reason>Versand</ram:Reason>");
+  });
+
+  test("Stornorechnung ist eine Gutschrift (381) mit Bezug, offen zur Erstattung", () => {
+    // Arrange
+    const data = input({
+      kind: "creditNote",
+      number: "ST-2026-0001",
+      precedingInvoice: { number: "RE-2026-0042", issuedAt: new Date(2026, 9, 1, 12, 0) },
+      paymentNote: "Der Betrag wird über die ursprüngliche Zahlungsart erstattet.",
+    });
+
+    // Act
+    const xml = ok(data);
+
+    // Assert
+    expect(xml).toContain("<ram:TypeCode>381</ram:TypeCode>");
+    expect(xml).toMatch(
+      /<ram:InvoiceReferencedDocument><ram:IssuerAssignedID>RE-2026-0042<\/ram:IssuerAssignedID><ram:FormattedIssueDateTime><qdt:DateTimeString format="102">20261001</
+    );
+    expect(single(xml, "ram:TotalPrepaidAmount")).toBe(0);
+    expect(single(xml, "ram:DuePayableAmount")).toBe(data.totalCents);
+  });
+
+  test("Kleinunternehmer: Kategorie E mit Befreiungsgrund", () => {
+    // Arrange
+    const items = [{ name: "Honig", quantity: 1, totalCents: 1000, vatRatePercent: 0 }];
+
+    // Act
+    const xml = ok(input({ items, shippingCents: 0, discountCents: 0, totalCents: 1000 }));
+
+    // Assert
+    expect(values(xml, "ram:CategoryCode").every((code) => code === "E")).toBe(true);
+    expect(xml).toContain("§ 19 UStG");
+    expect(single(xml, "ram:TaxTotalAmount")).toBe(0);
+  });
+
+  test("ohne USt-IdNr. oder mit Position ohne Steuersatz keine E-Rechnung", () => {
+    expect(buildCiiXml(input({ seller: { ...input().seller, vatId: " " } }))).toMatchObject({ ok: false });
+    const items = [{ name: "Alt", quantity: 1, totalCents: 1000, vatRatePercent: null }];
+    expect(buildCiiXml(input({ items, shippingCents: 0, discountCents: 0, totalCents: 1000 }))).toMatchObject({ ok: false });
+  });
+
+  test("Sonderzeichen im Namen werden maskiert", () => {
+    // Act
+    const xml = ok(input({ buyer: { ...input().buyer, name: 'Müller & Söhne <GmbH> "Bio"' } }));
+
+    // Assert
+    expect(xml).toContain("<ram:Name>Müller &amp; Söhne &lt;GmbH&gt; &quot;Bio&quot;</ram:Name>");
+  });
+});
+
+describe("Hilfsfunktionen", () => {
+  test("amount formatiert Cent ohne Gleitkommafehler", () => {
+    expect(amount(0)).toBe("0.00");
+    expect(amount(5)).toBe("0.05");
+    expect(amount(123456)).toBe("1234.56");
+    expect(amount(-250)).toBe("-2.50");
+  });
+
+  test("escapeXml maskiert alle fuenf Sonderzeichen", () => {
+    expect(escapeXml(`<a href="x">'&'</a>`)).toBe("&lt;a href=&quot;x&quot;&gt;&apos;&amp;&apos;&lt;/a&gt;");
+  });
+});

src/lib/einvoice/cii.ts

@@ -0,0 +1,317 @@
+import { distributeCents, splitGross, vatLinesWithShares } from "@/lib/vat";
+
+/**
+ * E-Rechnung nach EN 16931 als UN/CEFACT Cross Industry Invoice (CII D16B),
+ * Profil "EN 16931" (ZUGFeRD 2.x COMFORT / Factur-X). Das XML wird in das
+ * Rechnungs-PDF eingebettet (lib/einvoice/facturx-pdf.ts); PDF und XML
+ * zusammen sind die hybride E-Rechnung, das XML ist der massgebliche Teil.
+ *
+ * Die Shop-Preise sind Bruttopreise, EN 16931 rechnet netto. Damit XML und PDF
+ * auf den Cent dieselben Summen tragen, kommen Netto und Steuer je Satz
+ * unveraendert aus der Aufstellung des PDFs (lib/vat.ts); nur die Aufteilung
+ * auf die Positionen wird hier gerechnet:
+ *   Netto der Waren je Satz = Netto des Satzes - Versand netto + Rabatt netto,
+ * centgenau verteilt nach den Bruttobetraegen der Positionen. Versand und
+ * Rabatt stehen als Zu- und Abschlag auf Belegebene, je Satz.
+ *
+ * Eine Stornorechnung ist eine Gutschrift (Typ 381) mit positiven Betraegen
+ * und Verweis auf die aufgehobene Rechnung (BT-25/BT-26).
+ */
+
+export const EN16931_GUIDELINE_ID = "urn:cen.eu:en16931:2017";
+export const FACTURX_FILENAME = "factur-x.xml";
+
+const NS = {
+  rsm: "urn:un:unece:uncefact:data:standard:CrossIndustryInvoice:100",
+  ram: "urn:un:unece:uncefact:data:standard:ReusableAggregateBusinessInformationEntity:100",
+  qdt: "urn:un:unece:uncefact:data:standard:QualifiedDataType:100",
+  udt: "urn:un:unece:uncefact:data:standard:UnqualifiedDataType:100",
+} as const;
+
+const TYPE_CODE = { invoice: "380", creditNote: "381" } as const;
+/** UN/ECE Rec. 20: Stueck. */
+const UNIT_PIECE = "H87";
+const SMALL_BUSINESS_REASON = "Kein Ausweis von Umsatzsteuer, da Kleinunternehmer gemäß § 19 UStG";
+
+export type EInvoiceKind = keyof typeof TYPE_CODE;
+
+export interface EInvoiceParty {
+  name: string;
+  street: string;
+  zip: string;
+  city: string;
+  /** ISO 3166-1 alpha-2, z. B. "DE". */
+  countryCode: string;
+}
+
+export interface EInvoiceSeller extends EInvoiceParty {
+  vatId: string;
+  email?: string | null;
+}
+
+export interface EInvoiceItem {
+  name: string;
+  quantity: number;
+  /** Bruttobetrag der Position in Cent. */
+  totalCents: number;
+  vatRatePercent: number | null;
+}
+
+export interface EInvoiceInput {
+  kind: EInvoiceKind;
+  number: string;
+  issuedAt: Date;
+  currency: string;
+  orderNumber: string;
+  seller: EInvoiceSeller;
+  buyer: EInvoiceParty;
+  items: EInvoiceItem[];
+  /** Brutto, wie in der Bestellung. */
+  shippingCents: number;
+  discountCents: number;
+  discountCode?: string | null;
+  /** Rechnungsbetrag brutto; muss der Summe der Steueraufstellung entsprechen. */
+  totalCents: number;
+  /** Nur bei der Stornorechnung: die aufgehobene Rechnung. */
+  precedingInvoice?: { number: string; issuedAt: Date };
+  /** Zahlungsbedingungen (BT-20), z. B. "Bezahlt über Stripe". */
+  paymentNote: string;
+}
+
+export type EInvoiceResult = { ok: true; xml: string } | { ok: false; reason: string };
+
+export function escapeXml(value: string): string {
+  return value
+    .replace(/&/g, "&")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;")
+    .replace(/'/g, "&apos;");
+}
+
+/** Cent als Dezimalbetrag mit zwei Stellen, ohne Gleitkomma. */
+export function amount(cents: number): string {
+  const sign = cents < 0 ? "-" : "";
+  const abs = Math.abs(cents);
+  return `${sign}${Math.floor(abs / 100)}.${String(abs % 100).padStart(2, "0")}`;
+}
+
+/** Nettopreis je Stueck mit vier Nachkommastellen (Zehntausendstel Euro). */
+function unitPrice(lineNetCents: number, quantity: number): string {
+  const tenThousandths = Math.round((lineNetCents * 100) / quantity);
+  return `${Math.floor(tenThousandths / 10000)}.${String(tenThousandths % 10000).padStart(4, "0")}`;
+}
+
+/** Datum im Format 102 (JJJJMMTT), Kalendertag wie auf dem PDF (lib/format.ts). */
+function date102(value: Date): string {
+  const month = String(value.getMonth() + 1).padStart(2, "0");
+  const day = String(value.getDate()).padStart(2, "0");
+  return `${value.getFullYear()}${month}${day}`;
+}
+
+function percent(value: number): string {
+  return value.toFixed(2);
+}
+
+function tag(name: string, content: string, attributes = ""): string {
+  return `<${name}${attributes}>${content}</${name}>`;
+}
+
+function text(name: string, value: string, attributes = ""): string {
+  return tag(name, escapeXml(value), attributes);
+}
+
+interface TaxCategory {
+  code: "S" | "E";
+  ratePercent: number;
+}
+
+interface RateBlock {
+  category: TaxCategory;
+  netCents: number;
+  vatCents: number;
+  shippingNetCents: number;
+  discountNetCents: number;
+  lines: { item: EInvoiceItem; netCents: number }[];
+}
+
+function categoryXml(category: TaxCategory): string {
+  return (
+    text("ram:TypeCode", "VAT") +
+    text("ram:CategoryCode", category.code) +
+    text("ram:RateApplicablePercent", percent(category.ratePercent))
+  );
+}
+
+function partyXml(party: EInvoiceParty, extra = ""): string {
+  const address =
+    text("ram:PostcodeCode", party.zip) +
+    text("ram:LineOne", party.street) +
+    text("ram:CityName", party.city) +
+    text("ram:CountryID", party.countryCode);
+  return text("ram:Name", party.name) + tag("ram:PostalTradeAddress", address) + extra;
+}
+
+function lineXml(index: number, line: RateBlock["lines"][number], category: TaxCategory): string {
+  return tag(
+    "ram:IncludedSupplyChainTradeLineItem",
+    tag("ram:AssociatedDocumentLineDocument", text("ram:LineID", String(index))) +
+      tag("ram:SpecifiedTradeProduct", text("ram:Name", line.item.name)) +
+      tag(
+        "ram:SpecifiedLineTradeAgreement",
+        tag("ram:NetPriceProductTradePrice", text("ram:ChargeAmount", unitPrice(line.netCents, line.item.quantity)))
+      ) +
+      tag("ram:SpecifiedLineTradeDelivery", text("ram:BilledQuantity", String(line.item.quantity), ` unitCode="${UNIT_PIECE}"`)) +
+      tag(
+        "ram:SpecifiedLineTradeSettlement",
+        tag("ram:ApplicableTradeTax", categoryXml(category)) +
+          tag("ram:SpecifiedTradeSettlementLineMonetarySummation", text("ram:LineTotalAmount", amount(line.netCents)))
+      )
+  );
+}
+
+function allowanceChargeXml(isCharge: boolean, netCents: number, reason: string, category: TaxCategory): string {
+  return tag(
+    "ram:SpecifiedTradeAllowanceCharge",
+    tag("ram:ChargeIndicator", tag("udt:Indicator", isCharge ? "true" : "false")) +
+      text("ram:ActualAmount", amount(netCents)) +
+      text("ram:Reason", reason) +
+      tag("ram:CategoryTradeTax", categoryXml(category))
+  );
+}
+
+function headerTaxXml(block: RateBlock): string {
+  return tag(
+    "ram:ApplicableTradeTax",
+    text("ram:CalculatedAmount", amount(block.vatCents)) +
+      text("ram:TypeCode", "VAT") +
+      (block.category.code === "E" ? text("ram:ExemptionReason", SMALL_BUSINESS_REASON) : "") +
+      text("ram:BasisAmount", amount(block.netCents)) +
+      text("ram:CategoryCode", block.category.code) +
+      text("ram:RateApplicablePercent", percent(block.category.ratePercent))
+  );
+}
+
+/**
+ * Steuerbloecke je Satz, oder die Begruendung, warum sich keine gueltige
+ * E-Rechnung bilden laesst (Position ohne Satz, steuerfrei gemischt mit
+ * steuerpflichtig, Summen passen nicht).
+ */
+function rateBlocks(input: EInvoiceInput): RateBlock[] | string {
+  const lines = vatLinesWithShares(input);
+  if (!lines || lines.length === 0) return "Positionen ohne Steuersatz";
+  const exempt = lines.filter((line) => line.ratePercent === 0);
+  if (exempt.length > 0 && exempt.length !== lines.length) {
+    return "Steuerfreie und steuerpflichtige Positionen gemischt";
+  }
+  const gross = lines.reduce((sum, line) => sum + line.grossCents, 0);
+  if (gross !== input.totalCents) return `Steueraufstellung ${gross} weicht vom Rechnungsbetrag ${input.totalCents} ab`;
+
+  return lines.map((line) => {
+    const category: TaxCategory = { code: line.ratePercent > 0 ? "S" : "E", ratePercent: line.ratePercent };
+    const shippingNetCents = splitGross(line.shippingCents, line.ratePercent).netCents;
+    const discountNetCents = splitGross(line.discountCents, line.ratePercent).netCents;
+    const items = input.items.filter((item) => item.vatRatePercent === line.ratePercent);
+    const goodsNet = line.netCents - shippingNetCents + discountNetCents;
+    const nets = distributeCents(goodsNet, items.map((item) => item.totalCents));
+    return {
+      category,
+      netCents: line.netCents,
+      vatCents: line.vatCents,
+      shippingNetCents,
+      discountNetCents,
+      lines: items.map((item, index) => ({ item, netCents: nets[index] })),
+    };
+  });
+}
+
+function settlementXml(input: EInvoiceInput, blocks: RateBlock[]): string {
+  const discountReason = input.discountCode ? `Rabatt (${input.discountCode})` : "Rabatt";
+  const allowancesCharges = blocks
+    .flatMap((block) => [
+      block.shippingNetCents ? allowanceChargeXml(true, block.shippingNetCents, "Versand", block.category) : "",
+      block.discountNetCents ? allowanceChargeXml(false, block.discountNetCents, discountReason, block.category) : "",
+    ])
+    .join("");
+
+  const sum = (pick: (block: RateBlock) => number) => blocks.reduce((total, block) => total + pick(block), 0);
+  const lineTotal = sum((block) => block.lines.reduce((total, line) => total + line.netCents, 0));
+  const taxBasis = sum((block) => block.netCents);
+  const taxTotal = sum((block) => block.vatCents);
+  const grandTotal = taxBasis + taxTotal;
+  // Rechnung: per Stripe bereits bezahlt. Stornorechnung: der Betrag geht an die Kundschaft zurueck.
+  const prepaid = input.kind === "invoice" ? grandTotal : 0;
+
+  const reference = input.precedingInvoice
+    ? tag(
+        "ram:InvoiceReferencedDocument",
+        text("ram:IssuerAssignedID", input.precedingInvoice.number) +
+          tag("ram:FormattedIssueDateTime", text("qdt:DateTimeString", date102(input.precedingInvoice.issuedAt), ' format="102"'))
+      )
+    : "";
+
+  return (
+    text("ram:InvoiceCurrencyCode", input.currency) +
+    blocks.map(headerTaxXml).join("") +
+    allowancesCharges +
+    tag("ram:SpecifiedTradePaymentTerms", text("ram:Description", input.paymentNote)) +
+    tag(
+      "ram:SpecifiedTradeSettlementHeaderMonetarySummation",
+      text("ram:LineTotalAmount", amount(lineTotal)) +
+        text("ram:ChargeTotalAmount", amount(sum((block) => block.shippingNetCents))) +
+        text("ram:AllowanceTotalAmount", amount(sum((block) => block.discountNetCents))) +
+        text("ram:TaxBasisTotalAmount", amount(taxBasis)) +
+        text("ram:TaxTotalAmount", amount(taxTotal), ` currencyID="${escapeXml(input.currency)}"`) +
+        text("ram:GrandTotalAmount", amount(grandTotal)) +
+        text("ram:TotalPrepaidAmount", amount(prepaid)) +
+        text("ram:DuePayableAmount", amount(grandTotal - prepaid))
+    ) +
+    reference
+  );
+}
+
+export function buildCiiXml(input: EInvoiceInput): EInvoiceResult {
+  if (!input.seller.vatId.trim()) return { ok: false, reason: "USt-IdNr. des Shops fehlt (Einstellungen > Firma)" };
+  if (input.kind === "creditNote" && !input.precedingInvoice) return { ok: false, reason: "Stornorechnung ohne Bezug" };
+  const blocks = rateBlocks(input);
+  if (typeof blocks === "string") return { ok: false, reason: blocks };
+
+  let lineIndex = 0;
+  const lineItems = blocks.flatMap((block) => block.lines.map((line) => lineXml(++lineIndex, line, block.category))).join("");
+  const seller = input.seller;
+  const sellerExtra =
+    (seller.email ? tag("ram:URIUniversalCommunication", text("ram:URIID", seller.email, ' schemeID="EM"')) : "") +
+    tag("ram:SpecifiedTaxRegistration", text("ram:ID", seller.vatId.trim(), ' schemeID="VA"'));
+  const note = input.precedingInvoice
+    ? tag("ram:IncludedNote", text("ram:Content", `Stornorechnung zur Rechnung ${input.precedingInvoice.number}`))
+    : "";
+
+  const body =
+    tag(
+      "rsm:ExchangedDocumentContext",
+      tag("ram:GuidelineSpecifiedDocumentContextParameter", text("ram:ID", EN16931_GUIDELINE_ID))
+    ) +
+    tag(
+      "rsm:ExchangedDocument",
+      text("ram:ID", input.number) +
+        text("ram:TypeCode", TYPE_CODE[input.kind]) +
+        tag("ram:IssueDateTime", text("udt:DateTimeString", date102(input.issuedAt), ' format="102"')) +
+        note
+    ) +
+    tag(
+      "rsm:SupplyChainTradeTransaction",
+      lineItems +
+        tag(
+          "ram:ApplicableHeaderTradeAgreement",
+          tag("ram:SellerTradeParty", partyXml(seller, sellerExtra)) +
+            tag("ram:BuyerTradeParty", partyXml(input.buyer)) +
+            tag("ram:BuyerOrderReferencedDocument", text("ram:IssuerAssignedID", input.orderNumber))
+        ) +
+        tag("ram:ApplicableHeaderTradeDelivery", "") +
+        tag("ram:ApplicableHeaderTradeSettlement", settlementXml(input, blocks))
+    );
+  const namespaces = Object.entries(NS)
+    .map(([prefix, uri]) => ` xmlns:${prefix}="${uri}"`)
+    .join("");
+  return { ok: true, xml: `<?xml version="1.0" encoding="UTF-8"?>\n${tag("rsm:CrossIndustryInvoice", body, namespaces)}` };
+}

src/lib/einvoice/facturx-pdf.ts

@@ -0,0 +1,114 @@
+import { readFileSync } from "node:fs";
+import path from "node:path";
+import { FACTURX_FILENAME } from "@/lib/einvoice/cii";
+
+/**
+ * PDF/A-3b mit eingebettetem Factur-X-XML (ZUGFeRD 2.x, Profil EN 16931).
+ *
+ * PDF/A verlangt eingebettete Schriften; die 14 Standardschriften von pdfkit
+ * (Helvetica, Times) sind das nicht. Statt ihrer werden Liberation Sans und
+ * Liberation Serif eingebettet (SIL Open Font License, assets/fonts), die
+ * dieselben Laufweiten haben — das Layout der Rechnung bleibt unveraendert.
+ * Sie werden unter den Namen der Standardschriften registriert, damit der
+ * Zeichencode (font("Helvetica-Bold") usw.) gleich bleibt.
+ */
+
+const FONT_DIR = path.join(/*turbopackIgnore: true*/ process.cwd(), "assets", "fonts");
+
+const FONT_FILES = {
+  Helvetica: "LiberationSans-Regular.ttf",
+  "Helvetica-Bold": "LiberationSans-Bold.ttf",
+  "Times-Roman": "LiberationSerif-Regular.ttf",
+  "Times-Italic": "LiberationSerif-Italic.ttf",
+} as const;
+
+type FontName = keyof typeof FONT_FILES;
+
+let fontCache: Record<FontName, Buffer> | null = null;
+
+function fonts(): Record<FontName, Buffer> {
+  if (!fontCache) {
+    const entries = Object.entries(FONT_FILES).map(([name, file]) => [name, readFileSync(path.join(FONT_DIR, file))]);
+    fontCache = Object.fromEntries(entries) as Record<FontName, Buffer>;
+  }
+  return fontCache;
+}
+
+/**
+ * Optionen fuer new PDFDocument(): PDF/A-3b und eine eingebettete Grundschrift.
+ * Ohne "font" laedt pdfkit beim Anlegen die Standard-Helvetica, die dann
+ * nicht eingebettet im Dokument stuende.
+ */
+export function pdfaOptions(): PDFKit.PDFDocumentOptions {
+  return { pdfVersion: "1.7", subset: "PDF/A-3b", font: path.join(FONT_DIR, FONT_FILES.Helvetica) };
+}
+
+/** Registriert die eingebetteten Schriften unter den Namen der Standardschriften. */
+export function registerEmbeddedFonts(doc: PDFKit.PDFDocument): void {
+  for (const [name, data] of Object.entries(fonts())) {
+    doc.registerFont(name, data);
+  }
+}
+
+/** pdfkit schreibt Titel und Autor ungeprueft in die XMP-Metadaten; dort duerfen sie kein XML aufbrechen. */
+export function xmpSafe(value: string): string {
+  return value.replace(/[<>&]/g, " ").replace(/\s+/g, " ").trim();
+}
+
+const FX_NAMESPACE = "urn:factur-x:pdfa:CrossIndustryDocument:invoice:1p0#";
+
+function fxProperty(name: string, description: string): string {
+  return `
+              <rdf:li rdf:parseType="Resource">
+                <pdfaProperty:name>${name}</pdfaProperty:name>
+                <pdfaProperty:valueType>Text</pdfaProperty:valueType>
+                <pdfaProperty:category>external</pdfaProperty:category>
+                <pdfaProperty:description>${description}</pdfaProperty:description>
+              </rdf:li>`;
+}
+
+/**
+ * Bettet das XML als factur-x.xml ein (AFRelationship "Alternative", wie
+ * ZUGFeRD es fuer Deutschland vorsieht) und traegt die Factur-X-Angaben samt
+ * PDF/A-Erweiterungsschema in die XMP-Metadaten ein. Vor doc.end() aufrufen.
+ */
+export function embedFacturX(doc: PDFKit.PDFDocument, xml: string, issuedAt: Date): void {
+  // "relationship" kennt pdfkit (AFRelationship), die Typdefinition noch nicht.
+  const options: PDFKit.Mixins.PDFAttachmentOptions & { relationship: string } = {
+    name: FACTURX_FILENAME,
+    type: "text/xml",
+    relationship: "Alternative",
+    description: "Factur-X / ZUGFeRD invoice (EN 16931)",
+    creationDate: issuedAt,
+    modifiedDate: issuedAt,
+  };
+  doc.file(Buffer.from(xml, "utf8"), options);
+  doc.appendXML(`
+        <rdf:Description xmlns:fx="${FX_NAMESPACE}" rdf:about="">
+            <fx:DocumentType>INVOICE</fx:DocumentType>
+            <fx:DocumentFileName>${FACTURX_FILENAME}</fx:DocumentFileName>
+            <fx:Version>1.0</fx:Version>
+            <fx:ConformanceLevel>EN 16931</fx:ConformanceLevel>
+        </rdf:Description>
+        <rdf:Description xmlns:pdfaExtension="http://www.aiim.org/pdfa/ns/extension/" xmlns:pdfaSchema="http://www.aiim.org/pdfa/ns/schema#" xmlns:pdfaProperty="http://www.aiim.org/pdfa/ns/property#" rdf:about="">
+          <pdfaExtension:schemas>
+            <rdf:Bag>
+              <rdf:li rdf:parseType="Resource">
+                <pdfaSchema:schema>Factur-X PDFA Extension Schema</pdfaSchema:schema>
+                <pdfaSchema:namespaceURI>${FX_NAMESPACE}</pdfaSchema:namespaceURI>
+                <pdfaSchema:prefix>fx</pdfaSchema:prefix>
+                <pdfaSchema:property>
+                  <rdf:Seq>${[
+                    fxProperty("DocumentFileName", "The name of the embedded XML document"),
+                    fxProperty("DocumentType", "The type of the hybrid document in capital letters, e.g. INVOICE or ORDER"),
+                    fxProperty("Version", "The actual version of the standard applying to the embedded XML document"),
+                    fxProperty("ConformanceLevel", "The conformance level of the embedded XML document"),
+                  ].join("")}
+                  </rdf:Seq>
+                </pdfaSchema:property>
+              </rdf:li>
+            </rdf:Bag>
+          </pdfaExtension:schemas>
+        </rdf:Description>
+        `);
+}

src/lib/erp-export.ts

@@ -3,7 +3,7 @@ import type { Prisma } from "@/generated/prisma/client";
 import { prisma } from "@/lib/prisma";
 import { generateInvoicePdf } from "@/lib/invoice-pdf";
 import { readStoredInvoicePdf } from "@/lib/invoice-storage";
-import { vatBreakdown, type VatBreakdownLine } from "@/lib/vat";
+import { vatLinesWithShares, type VatLineWithShares } from "@/lib/vat";
 import { isLocale, defaultLocale } from "@/i18n/config";
 
 /**
@@ -57,40 +57,10 @@ const invoiceInclude = {
 
 type ErpInvoiceRecord = Prisma.InvoiceGetPayload<{ include: typeof invoiceInclude }>;
 
-export interface ErpVatLine extends VatBreakdownLine {
+export type ErpVatLine = VatLineWithShares;
-  /** Darin enthaltener Versandanteil (brutto). */
-  shippingCents: number;
-  /** Davon abgezogener Rabattanteil (brutto). */
-  discountCents: number;
-}
 
-/**
+/** Umsatzsteuer je Satz mit Versand- und Rabattanteil, siehe lib/vat.ts. */
- * Umsatzsteuer je Satz wie auf der Rechnung (lib/vat.ts), dazu der Versand-
+export const erpVatLines = vatLinesWithShares;
- * und der Rabattanteil je Satz. Beide Anteile ergeben sich aus derselben
- * Rechnung ohne den jeweils anderen Betrag, also ohne eigene Verteilungslogik.
- * null, wenn eine Position keinen Steuersatz hat (Bestellungen aus der Zeit
- * vor der Steuerausweisung).
- */
-export function erpVatLines(order: {
-  items: ReadonlyArray<{ totalCents: number; vatRatePercent: number | null }>;
-  shippingCents: number;
-  discountCents: number;
-}): ErpVatLine[] | null {
-  const items: { totalCents: number; vatRatePercent: number }[] = [];
-  for (const item of order.items) {
-    if (item.vatRatePercent == null) return null;
-    items.push({ totalCents: item.totalCents, vatRatePercent: item.vatRatePercent });
-  }
-  const full = vatBreakdown({ items, shippingCents: order.shippingCents, discountCents: order.discountCents });
-  const plain = vatBreakdown({ items, shippingCents: 0, discountCents: 0 });
-  const withShipping = vatBreakdown({ items, shippingCents: order.shippingCents, discountCents: 0 });
-  const withDiscount = vatBreakdown({ items, shippingCents: 0, discountCents: order.discountCents });
-  return full.map((line, index) => ({
-    ...line,
-    shippingCents: withShipping[index].grossCents - plain[index].grossCents,
-    discountCents: plain[index].grossCents - withDiscount[index].grossCents,
-  }));
-}
 
 /** Rechnung fuer ERPNext; bewusst ohne Telefonnummer, Postnummer und Notizen (nicht buchungsrelevant). */
 export function toErpInvoice(invoice: ErpInvoiceRecord) {

src/lib/invoice-pdf.test.ts

@@ -1,3 +1,10 @@
+// @vitest-environment node
+//
+// Abweichend von der globalen jsdom-Umgebung (vitest.config.ts): pdfkit
+// erkennt die eingebetteten Schriften an "instanceof Uint8Array", und unter
+// jsdom stammt der Buffer aus einem anderen JS-Realm — die Pruefung schluege
+// fehl ("Not a supported font format"). Im Server laeuft ohnehin Node.
+import { inflateSync } from "node:zlib";
 import { describe, test, expect, vi } from "vitest";
 
 vi.mock("@/lib/company-info", () => ({
@@ -78,4 +85,53 @@ describe("generateInvoicePdf", () => {
     expect(pages).toBeGreaterThanOrEqual(2);
     expect(pages).toBeLessThanOrEqual(3);
   });
+
+  test("ist eine E-Rechnung: PDF/A-3b mit eingebettetem factur-x.xml (EN 16931)", async () => {
+    // Act
+    const pdf = await generateInvoicePdf(input([item(1, 7), item(2, 19)]));
+
+    // Assert
+    const raw = pdf.toString("latin1");
+    expect(raw).toContain("<pdfaid:part>3</pdfaid:part>");
+    expect(raw).toContain("<fx:ConformanceLevel>EN 16931</fx:ConformanceLevel>");
+    expect(raw).toMatch(/\/AFRelationship \/Alternative/);
+    expect(raw).toContain("/OutputIntents");
+    const xml = embeddedXml(pdf);
+    expect(xml).toContain("<ram:ID>RE-TEST-1</ram:ID>");
+    expect(xml).toContain("<ram:TypeCode>380</ram:TypeCode>");
+    expect(xml).toContain("<ram:GrandTotalAmount>24.90</ram:GrandTotalAmount>");
+  });
+
+  test("bettet alle Schriften ein (keine Standardschrift ohne Einbettung)", async () => {
+    // Act
+    const raw = (await generateInvoicePdf(input([item(1, 7)]))).toString("latin1");
+
+    // Assert: eingebettete Teilschriften tragen ein Praefix wie "ABCDEF+".
+    const baseFonts = [...raw.matchAll(/\/BaseFont \/([^\s/>]+)/g)].map((match) => match[1]);
+    expect(baseFonts.length).toBeGreaterThan(0);
+    expect(baseFonts.every((name) => /^[A-Z]{6}\+Liberation/.test(name))).toBe(true);
+    expect(raw).toContain("/FontFile2");
+  });
+
+  test("Stornorechnung: Gutschrift mit Bezug auf die Rechnung", async () => {
+    // Act
+    const pdf = await generateInvoicePdf({
+      ...input([item(1, 7)]),
+      cancellation: { number: "ST-TEST-1", issuedAt: new Date("2026-10-05T00:00:00Z") },
+    });
+
+    // Assert
+    const xml = embeddedXml(pdf);
+    expect(xml).toContain("<ram:ID>ST-TEST-1</ram:ID>");
+    expect(xml).toContain("<ram:TypeCode>381</ram:TypeCode>");
+    expect(xml).toContain("<ram:IssuerAssignedID>RE-TEST-1</ram:IssuerAssignedID>");
+    expect(pdf.toString("latin1")).toContain("Stornorechnung ST-TEST-1");
+  });
 });
+
+/** Das eingebettete factur-x.xml (Stream des EmbeddedFile, deflate-komprimiert). */
+function embeddedXml(pdf: Buffer): string {
+  const match = /\/Type \/EmbeddedFile[\s\S]*?stream\r?\n([\s\S]*?)\r?\nendstream/.exec(pdf.toString("latin1"));
+  if (!match) throw new Error("kein eingebettetes XML");
+  return inflateSync(Buffer.from(match[1], "latin1")).toString("utf8");
+}

src/lib/invoice-pdf.ts

@@ -5,6 +5,8 @@ import { getDictionary } from "@/i18n/get-dictionary";
 import { invoiceVatBreakdown, type VatBreakdownLine } from "@/lib/vat";
 import { groupInvoiceItemsByVatRate, type InvoiceItemGroup } from "@/lib/invoice-groups";
 import { INVOICE_COLORS as C, loadInvoiceLogo, drawInvoiceLogo, type InvoiceLogo } from "@/lib/invoice-pdf-brand";
+import { buildCiiXml, type EInvoiceResult } from "@/lib/einvoice/cii";
+import { embedFacturX, pdfaOptions, registerEmbeddedFonts, xmpSafe } from "@/lib/einvoice/facturx-pdf";
 import type { Dictionary } from "@/i18n/dictionary-type";
 import type { Locale } from "@/i18n/config";
 
@@ -30,6 +32,8 @@ interface InvoicePdfInput {
     street: string;
     zip: string;
     city: string;
+    /** ISO-Laendercode der Rechnungsanschrift; fehlt er, gilt Deutschland. */
+    country?: string;
     currency: string;
     subtotalCents: number;
     shippingCents: number;
@@ -37,6 +41,11 @@ interface InvoicePdfInput {
     discountCode?: { code: string } | null;
     items: InvoiceItem[];
   };
+  /**
+   * Gesetzt bei der Stornorechnung: sie hebt die Rechnung invoiceNumber vom
+   * issuedAt auf und traegt alle Betraege mit umgekehrtem Vorzeichen.
+   */
+  cancellation?: { number: string; issuedAt: Date };
 }
 
 type Company = Awaited<ReturnType<typeof getCompanyInfo>>;
@@ -44,9 +53,16 @@ type Company = Awaited<ReturnType<typeof getCompanyInfo>>;
 interface Ctx {
   doc: PDFKit.PDFDocument;
   t: Dictionary["invoicePage"];
+  /** Betrag mit dem Vorzeichen des Belegs (Stornorechnung negativ). */
   money: (cents: number) => string;
+  /** Betrag ohne Vorzeichenumkehr. */
+  plain: (cents: number) => string;
+  isCancellation: boolean;
 }
 
+/** Sitz des Shops; die Firmenanschrift in den Einstellungen hat kein Land. */
+const SELLER_COUNTRY_CODE = "DE";
+
 // A4 in Punkt. Ab FOOTER_TOP beginnt die Fusszeile; was oberhalb von
 // CONTENT_BOTTOM nicht mehr hinpasst, wandert auf die naechste Seite.
 const PAGE_WIDTH = 595.28;
@@ -84,12 +100,17 @@ const COL = {
 export async function generateInvoicePdf(input: InvoicePdfInput): Promise<Buffer> {
   const t = getDictionary(input.locale).invoicePage;
   const [company, logo] = await Promise.all([getCompanyInfo(), loadInvoiceLogo()]);
+  const title = input.cancellation
+    ? `${t.cancellationTitle} ${input.cancellation.number}`
+    : `${t.documentTitle} ${input.invoiceNumber}`;
   const doc = new PDFDocument({
+    ...pdfaOptions(),
     margin: MARGIN,
     size: "A4",
     bufferPages: true,
-    info: { Title: `${t.documentTitle} ${input.invoiceNumber}`, Author: company.name },
+    info: { Title: xmpSafe(title), Author: xmpSafe(company.name) },
   });
+  registerEmbeddedFonts(doc);
   const chunks: Buffer[] = [];
   doc.on("data", (chunk: Buffer) => chunks.push(chunk));
   const done = new Promise<Buffer>((resolve, reject) => {
@@ -97,7 +118,9 @@ export async function generateInvoicePdf(input: InvoicePdfInput): Promise<Buffer
     doc.on("error", reject);
   });
 
-  const ctx: Ctx = { doc, t, money: (cents) => formatPrice(cents, input.order.currency) };
+  const sign = input.cancellation ? -1 : 1;
+  const plain = (cents: number) => formatPrice(cents, input.order.currency);
+  const ctx: Ctx = { doc, t, money: (cents) => plain(sign * cents), plain, isCancellation: Boolean(input.cancellation) };
   const breakdown = invoiceVatBreakdown(input.order);
 
   drawHeader(ctx, company, logo);
@@ -106,13 +129,65 @@ export async function generateInvoicePdf(input: InvoicePdfInput): Promise<Buffer
   let y = drawTableHeader(ctx, Math.max(addressBottom, metaBottom) + 30);
   y = drawItems(ctx, groupInvoiceItemsByVatRate(input.order.items), y);
   y = drawSummary(ctx, input, breakdown, y + 22);
-  drawClosing(ctx, breakdown, y + 26);
+  drawClosing(ctx, input, breakdown, y + 26);
   drawFooters(ctx, company);
 
+  const einvoice = eInvoiceXml(input, company);
+  if (einvoice.ok) {
+    embedFacturX(doc, einvoice.xml, input.cancellation?.issuedAt ?? input.issuedAt);
+  } else {
+    console.warn(`[invoice-pdf] ${input.cancellation?.number ?? input.invoiceNumber} ohne E-Rechnung (nur PDF): ${einvoice.reason}`);
+  }
+
   doc.end();
   return done;
 }
 
+/**
+ * Das XML der E-Rechnung (EN 16931) aus denselben Daten wie das PDF. Die
+ * Stornorechnung ist eine Gutschrift mit Bezug auf die aufgehobene Rechnung.
+ */
+function eInvoiceXml(input: InvoicePdfInput, company: Company): EInvoiceResult {
+  const { order, cancellation } = input;
+  return buildCiiXml({
+    kind: cancellation ? "creditNote" : "invoice",
+    number: cancellation?.number ?? input.invoiceNumber,
+    issuedAt: cancellation?.issuedAt ?? input.issuedAt,
+    currency: order.currency,
+    orderNumber: order.orderNumber,
+    seller: {
+      name: company.name,
+      street: company.address.street,
+      zip: company.address.zip,
+      city: company.address.city,
+      countryCode: SELLER_COUNTRY_CODE,
+      vatId: company.vatId,
+      email: company.email,
+    },
+    buyer: {
+      name: `${order.firstName} ${order.lastName}`.trim(),
+      street: order.street,
+      zip: order.zip,
+      city: order.city,
+      countryCode: (order.country || SELLER_COUNTRY_CODE).toUpperCase(),
+    },
+    items: order.items.map((item) => ({
+      name: item.productName,
+      quantity: item.quantity,
+      totalCents: item.totalCents,
+      vatRatePercent: item.vatRatePercent,
+    })),
+    shippingCents: order.shippingCents,
+    discountCents: order.discountCents,
+    discountCode: order.discountCode?.code ?? null,
+    totalCents: input.totalCents,
+    precedingInvoice: cancellation ? { number: input.invoiceNumber, issuedAt: input.issuedAt } : undefined,
+    paymentNote: cancellation
+      ? "Der Betrag wird über die ursprüngliche Zahlungsart erstattet."
+      : "Bereits bezahlt (Online-Zahlung über Stripe).",
+  });
+}
+
 function label(ctx: Ctx, text: string, x: number, y: number): void {
   ctx.doc
     .font("Helvetica-Bold")
@@ -139,11 +214,19 @@ function drawHeader(ctx: Ctx, company: Company, logo: InvoiceLogo | null): void
     doc.font("Helvetica").fontSize(8.5).fillColor(C.honeyDark).text(company.claim, textX, 74, { width: 240, lineBreak: false });
   }
 
+  // "STORNORECHNUNG" ist laenger als "RECHNUNG": die Schrift wird so weit
+  // verkleinert, dass der Titel in einer Zeile rechts oben bleibt.
+  const title = (ctx.isCancellation ? t.cancellationTitle : t.documentTitle).toUpperCase();
+  const titleX = 300;
+  const titleOptions = { characterSpacing: 2 };
+  let titleSize = 26;
+  doc.font("Times-Roman").fontSize(titleSize);
+  while (titleSize > 14 && doc.widthOfString(title, titleOptions) > RIGHT - titleX) {
+    doc.fontSize(--titleSize);
+  }
   doc
-    .font("Times-Roman")
-    .fontSize(26)
     .fillColor(C.forest)
-    .text(t.documentTitle.toUpperCase(), 360, 48, { width: RIGHT - 360, align: "right", characterSpacing: 2, lineBreak: false });
+    .text(title, titleX, 48 + (26 - titleSize) / 2, { ...titleOptions, width: RIGHT - titleX, align: "right", lineBreak: false });
   hairline(ctx, MARGIN, RIGHT, 112, C.honey);
 }
 
@@ -165,9 +248,18 @@ function drawRecipient(ctx: Ctx, input: InvoicePdfInput, company: Company): numb
 /** Rechnungsdaten rechts oben, inklusive USt-IdNr. (§ 14 Abs. 4 Nr. 2 UStG). */
 function drawMetaBox(ctx: Ctx, input: InvoicePdfInput, company: Company): number {
   const { doc, t } = ctx;
-  const rows: [string, string][] = [
+  const documentRows: [string, string][] = input.cancellation
+    ? [
+        [t.cancellationNumberLabel, input.cancellation.number],
+        [t.cancellationDateLabel, formatDate(input.cancellation.issuedAt)],
+        [t.cancelsInvoiceLabel, input.invoiceNumber],
+      ]
+    : [
         [t.invoiceNumberLabel, input.invoiceNumber],
         [t.invoiceDateLabel, formatDate(input.issuedAt)],
+      ];
+  const rows: [string, string][] = [
+    ...documentRows,
     [t.orderNumberLabel, input.order.orderNumber],
     ...(company.vatId ? ([[t.vatIdLabel, company.vatId]] as [string, string][]) : []),
   ];
@@ -287,14 +379,16 @@ function drawSummary(ctx: Ctx, input: InvoicePdfInput, breakdown: VatBreakdownLi
 }
 
 function drawTotals(ctx: Ctx, input: InvoicePdfInput, top: number): number {
-  const { doc, t, money } = ctx;
+  const { doc, t, money, plain } = ctx;
   const { order } = input;
   const x = 330;
   const discountName = order.discountCode ? `${t.discountLabel} (${order.discountCode.code})` : t.discountLabel;
   const rows: [string, string][] = [
     [t.subtotalLabel, money(order.subtotalCents)],
     [t.shippingLabel, order.shippingCents === 0 ? t.freeShipping : money(order.shippingCents)],
-    ...(order.discountCents > 0 ? ([[discountName, `– ${money(order.discountCents)}`]] as [string, string][]) : []),
+    ...(order.discountCents > 0
+      ? ([[discountName, `${ctx.isCancellation ? "+" : "–"} ${plain(order.discountCents)}`]] as [string, string][])
+      : []),
   ];
 
   let y = top;
@@ -371,12 +465,20 @@ function drawTaxSummary(ctx: Ctx, breakdown: VatBreakdownLine[], top: number): n
   return y;
 }
 
-function drawClosing(ctx: Ctx, breakdown: VatBreakdownLine[], startY: number): void {
+function drawClosing(ctx: Ctx, input: InvoicePdfInput, breakdown: VatBreakdownLine[], startY: number): void {
   const { doc, t } = ctx;
   const y = ensureSpace(ctx, startY, 40, false);
   if (breakdown.some((line) => line.ratePercent > 0)) {
     doc.font("Helvetica").fontSize(8).fillColor(C.sage).text(t.pricesIncludeVat, MARGIN, y, { width: CONTENT_WIDTH });
   }
+  if (input.cancellation) {
+    doc
+      .font("Helvetica")
+      .fontSize(9.5)
+      .fillColor(C.ink)
+      .text(t.cancellationNote(input.invoiceNumber, formatDate(input.issuedAt)), MARGIN, y + 16, { width: CONTENT_WIDTH });
+    return;
+  }
   doc.font("Times-Italic").fontSize(13).fillColor(C.honeyDark).text(t.thankYou, MARGIN, y + 16, { width: CONTENT_WIDTH });
 }
 

src/lib/vat.ts

@@ -252,3 +252,46 @@ export function invoiceVatBreakdown(order: {
     discountCents: order.discountCents,
   });
 }
+
+export interface VatLineWithShares extends VatBreakdownLine {
+  /** Darin enthaltener Versandanteil (brutto). */
+  shippingCents: number;
+  /** Davon abgezogener Rabattanteil (brutto). */
+  discountCents: number;
+}
+
+/**
+ * Umsatzsteuer je Satz wie auf der Rechnung, dazu der Versand- und der
+ * Rabattanteil je Satz. Beide Anteile ergeben sich aus derselben Rechnung
+ * ohne den jeweils anderen Betrag, also ohne eigene Verteilungslogik — so
+ * stimmen sie mit der Aufstellung auf dem PDF auf den Cent ueberein.
+ * Gebraucht vom ERP-Export und von der E-Rechnung (lib/einvoice).
+ *
+ * null, wenn eine Position keinen Steuersatz hat (Bestellungen aus der Zeit
+ * vor der Steuerausweisung).
+ */
+export function vatLinesWithShares(order: {
+  items: ReadonlyArray<{ totalCents: number; vatRatePercent: number | null }>;
+  shippingCents: number;
+  discountCents: number;
+}): VatLineWithShares[] | null {
+  const items: { totalCents: number; vatRatePercent: number }[] = [];
+  for (const item of order.items) {
+    if (item.vatRatePercent == null) return null;
+    items.push({ totalCents: item.totalCents, vatRatePercent: item.vatRatePercent });
+  }
+  const full = vatBreakdown({ items, shippingCents: order.shippingCents, discountCents: order.discountCents });
+  const plain = vatBreakdown({ items, shippingCents: 0, discountCents: 0 });
+  const withShipping = vatBreakdown({ items, shippingCents: order.shippingCents, discountCents: 0 });
+  const withDiscount = vatBreakdown({ items, shippingCents: 0, discountCents: order.discountCents });
+  return full.map((line, index) => ({
+    ...line,
+    shippingCents: withShipping[index].grossCents - plain[index].grossCents,
+    discountCents: plain[index].grossCents - withDiscount[index].grossCents,
+  }));
+}
+
+/** Verteilt ganze Cents im Verhaeltnis der Gewichte (Hare-Niemeyer, siehe distributeProportionally). */
+export function distributeCents(amountCents: number, weights: readonly number[]): number[] {
+  return distributeProportionally(amountCents, weights);
+}