einfach-produktiv-invoicing/src/einvoice/buildEInvoiceData.ts

import type { Invoice } from "@e-invoice-eu/core";
import { computeTaxBreakdown } from "../taxBreakdown";
import type { InvoiceOrder } from "../invoicePdf";
import type { CorrectionInvoiceKind, CorrectionInvoiceOrder } from "../correctionInvoicePdf";
import type { InvoiceSeller } from "../seller";
import { countryCode } from "./countryCode";

// @e-invoice-eu/core only re-exports the top-level `Invoice` type, not the
// individual leaf field types (PaymentMeansTypeCode, SellerCountryCode,
// ...) — derived here via indexed access instead of reaching into the
// package's internal dist paths, which would be fragile against any
// future restructuring on their end.
type UblInvoice = Invoice["ubl:Invoice"];
type PaymentMeansTypeCode = NonNullable<UblInvoice["cac:PaymentMeans"]>[number]["cbc:PaymentMeansCode"];
type SellerCountryCode = UblInvoice["cac:AccountingSupplierParty"]["cac:Party"]["cac:PostalAddress"]["cac:Country"]["cbc:IdentificationCode"];
type BuyerCountryCode = UblInvoice["cac:AccountingCustomerParty"]["cac:Party"]["cac:PostalAddress"]["cac:Country"]["cbc:IdentificationCode"];

// EN16931 VAT category — 'S' ("Standard rated") is the correct code for
// *any* positive VAT rate under EN16931/Peppol BIS convention, not just
// the statutory default rate; the actual percentage (19%, 7%, ...) goes
// in the category's own `cbc:Percent`, not the code itself. This shop
// only ever sells goods at a positive German VAT rate — no exports,
// reverse-charge, or exempt sales exist yet — so every line and every
// summed group uses this same code.
const VAT_CATEGORY = "S";

// UN/ECE Recommendation 20 unit-of-measure code for "one" (a countable
// piece/unit) — this shop sells discrete products (ToDo-Karten sets,
// notebooks, ...), never anything sold by weight/length/volume, so every
// line uses the same code.
const UNIT_CODE = "C62";

// UNCL4461 payment-means codes — only the ones this shop's actual
// `payment-methods` collection can produce (see the Payload README's
// "Per-product tax rates"-adjacent Commerce section). '1' ("Instrument
// not defined") is the fallback for a payment method title this mapping
// doesn't recognize, not an error — new payment methods get added in
// Payload without a matching code deploy here otherwise breaking e-invoice
// generation entirely.
const PAYMENT_MEANS_CODE: Record<string, PaymentMeansTypeCode> = {
  Überweisung: "30", // SEPA credit transfer
  Kreditkarte: "48", // Bank card
  PayPal: "68", // Online payment service
};

function paymentMeansCode(paymentMethodTitle: string): PaymentMeansTypeCode {
  return PAYMENT_MEANS_CODE[paymentMethodTitle] ?? "1";
}

// EN16931 amount fields are XML-serialized strings, not numbers
// (confirmed against @e-invoice-eu/core's own generated types — every
// `*Amount`/`*Quantity`/`*Rate` type alias resolves to `string`),
// formatted to exactly 2 decimals — and every `*Amount` field turned out
// (at runtime, via the library's ajv schema — not visible in the .d.ts
// types at all) to *require* a sibling `*@currencyID` key the moment the
// amount itself is present. `amt()` returns both keys at once via object
// spread, so call sites can't add one without the other.
function amt(key: string, value: number): Record<string, string> {
  return { [key]: value.toFixed(2), [`${key}@currencyID`]: "EUR" };
}

// Same "runtime-required sibling key" story as `amt()`, but for
// `cbc:InvoicedQuantity@unitCode`.
function qty(value: number): Record<string, string> {
  return { "cbc:InvoicedQuantity": String(value), "cbc:InvoicedQuantity@unitCode": UNIT_CODE };
}

function isoDate(iso: string): string {
  return iso.slice(0, 10);
}

function paymentMeans(seller: InvoiceSeller, paymentMethodTitle: string): UblInvoice["cac:PaymentMeans"] {
  if (!seller.iban) return undefined;
  return [
    {
      "cbc:PaymentMeansCode": paymentMeansCode(paymentMethodTitle),
      "cac:PayeeFinancialAccount": {
        "cbc:ID": seller.iban,
        ...(seller.bankName ? { "cbc:Name": seller.bankName } : {}),
      },
    },
  ];
}

function sellerParty(seller: InvoiceSeller): UblInvoice["cac:AccountingSupplierParty"] {
  return {
    "cac:Party": {
      "cac:PostalAddress": {
        "cbc:StreetName": seller.sellerStreet,
        "cbc:CityName": seller.sellerCity,
        "cbc:PostalZone": seller.sellerZip,
        "cac:Country": { "cbc:IdentificationCode": countryCode(seller.sellerCountry) as SellerCountryCode },
      },
      "cac:PartyTaxScheme": [
        {
          "cbc:CompanyID": seller.vatId,
          "cac:TaxScheme": { "cbc:ID": "VAT" },
        },
      ],
      "cac:PartyLegalEntity": { "cbc:RegistrationName": seller.sellerName },
      "cac:Contact": { "cbc:ElectronicMail": seller.sellerEmail },
    },
  };
}

function buyerParty(name: string, street: string | null | undefined, zip: string, city: string, country: string): UblInvoice["cac:AccountingCustomerParty"] {
  return {
    "cac:Party": {
      "cac:PostalAddress": {
        ...(street ? { "cbc:StreetName": street } : {}),
        "cbc:CityName": city,
        "cbc:PostalZone": zip,
        "cac:Country": { "cbc:IdentificationCode": countryCode(country) as BuyerCountryCode },
      },
      "cac:PartyLegalEntity": { "cbc:RegistrationName": name },
    },
  };
}

function taxTotal(rateGroups: { rate: number; net: number; tax: number }[]): UblInvoice["cac:TaxTotal"] {
  const totalTax = rateGroups.reduce((sum, g) => sum + g.tax, 0);
  return [
    {
      ...amt("cbc:TaxAmount", totalTax),
      "cac:TaxSubtotal": rateGroups.map((g) => ({
        ...amt("cbc:TaxableAmount", g.net),
        ...amt("cbc:TaxAmount", g.tax),
        "cac:TaxCategory": {
          "cbc:ID": VAT_CATEGORY,
          "cbc:Percent": String(g.rate),
          "cac:TaxScheme": { "cbc:ID": "VAT" },
        },
      })),
    },
  ] as UblInvoice["cac:TaxTotal"];
}

function invoiceLines(
  lines: { productName: string; variantName?: string | null; quantity: number; unitPrice: number; taxRatePercent: number }[],
): UblInvoice["cac:InvoiceLine"] {
  return lines.map((item, i) => ({
    "cbc:ID": String(i + 1),
    ...qty(item.quantity),
    ...amt("cbc:LineExtensionAmount", item.quantity * item.unitPrice),
    "cac:Item": {
      "cbc:Name": item.variantName ? `${item.productName} (${item.variantName})` : item.productName,
      "cac:ClassifiedTaxCategory": {
        "cbc:ID": VAT_CATEGORY,
        "cbc:Percent": String(item.taxRatePercent),
        "cac:TaxScheme": { "cbc:ID": "VAT" },
      },
    },
    "cac:Price": amt("cbc:PriceAmount", item.unitPrice),
  })) as unknown as UblInvoice["cac:InvoiceLine"];
}

// Full original invoice — one line per order item, positive amounts,
// InvoiceTypeCode 380 ("Commercial invoice").
export function buildEInvoiceData(order: InvoiceOrder, seller: InvoiceSeller): Invoice {
  const rateGroups = computeTaxBreakdown(
    order.items.map((item) => ({ quantity: item.quantity, unitPrice: item.unitPrice, taxRatePercent: item.taxRatePercent })),
    order.subtotal,
    order.discountAmount,
    order.shippingCost,
  );
  const totalNet = rateGroups.reduce((sum, g) => sum + g.net, 0);
  const totalTax = rateGroups.reduce((sum, g) => sum + g.tax, 0);

  return {
    "ubl:Invoice": {
      "cbc:ID": order.invoiceNumber,
      "cbc:IssueDate": isoDate(order.invoiceIssuedAt),
      "cbc:InvoiceTypeCode": "380",
      "cbc:DocumentCurrencyCode": "EUR",
      "cac:AccountingSupplierParty": sellerParty(seller),
      "cac:AccountingCustomerParty": buyerParty(
        `${order.customerFirstName} ${order.customerLastName}`,
        order.deliveryMethod === "address" ? order.street : null,
        order.zip,
        order.city,
        order.country,
      ),
      "cac:PaymentMeans": paymentMeans(seller, order.paymentMethodTitle),
      "cac:TaxTotal": taxTotal(rateGroups),
      "cac:LegalMonetaryTotal": {
        ...amt("cbc:LineExtensionAmount", totalNet),
        ...amt("cbc:TaxExclusiveAmount", totalNet),
        ...amt("cbc:TaxInclusiveAmount", totalNet + totalTax),
        ...amt("cbc:PayableAmount", order.total),
      } as unknown as UblInvoice["cac:LegalMonetaryTotal"],
      "cac:InvoiceLine": invoiceLines(order.items),
    },
  };
}

// Stornorechnung/Gutschrift — same UBL `Invoice` shape (this library has
// no separate "credit note" type), but InvoiceTypeCode 381 ("Credit
// note") instead of 380, so a receiving AP system reads it as a
// reduction, not a second charge. Amounts stay positive (the credited
// amount, not a negative number) — EN16931/UBL convention puts the
// polarity in the type code, not the sign, same as the PDF's own visual
// "-{amount}" is a *display* convention layered on top of positive
// underlying numbers (see correctionInvoicePdf.tsx's groupByTaxRate()).
// Mirrors resolveLineItems()/groupByTaxRate() in correctionInvoicePdf.tsx
// exactly — same Stornorechnung-vs-Gutschrift policy (full reversal incl.
// shipping vs. only returned quantities, no shipping, no discount
// reproration) — deliberately not re-derived independently here.
export function buildCorrectionEInvoiceData(kind: CorrectionInvoiceKind, order: CorrectionInvoiceOrder, seller: InvoiceSeller): Invoice {
  const lines =
    kind === "storno"
      ? order.items.map((item) => ({ item, effectiveQuantity: item.quantity }))
      : order.items.filter((item) => (item.returnQuantity ?? 0) > 0).map((item) => ({ item, effectiveQuantity: item.returnQuantity as number }));

  const rateGroups = computeTaxBreakdown(
    lines.map(({ item, effectiveQuantity }) => ({ quantity: effectiveQuantity, unitPrice: item.unitPrice, taxRatePercent: item.taxRatePercent })),
    order.subtotal,
    kind === "storno" ? order.discountAmount : 0,
    kind === "storno" ? order.shippingCost : 0,
  );
  const totalNet = rateGroups.reduce((sum, g) => sum + g.net, 0);
  const totalTax = rateGroups.reduce((sum, g) => sum + g.tax, 0);
  const grandTotal = rateGroups.reduce((sum, g) => sum + g.gross, 0);

  return {
    "ubl:Invoice": {
      "cbc:ID": order.correctionInvoiceNumber,
      "cbc:IssueDate": isoDate(order.correctionInvoiceIssuedAt),
      "cbc:InvoiceTypeCode": "381",
      "cbc:DocumentCurrencyCode": "EUR",
      "cac:BillingReference": [
        {
          "cac:InvoiceDocumentReference": {
            "cbc:ID": order.invoiceNumber,
            "cbc:IssueDate": isoDate(order.invoiceIssuedAt),
          },
        },
      ],
      "cac:AccountingSupplierParty": sellerParty(seller),
      "cac:AccountingCustomerParty": buyerParty(
        `${order.customerFirstName} ${order.customerLastName}`,
        order.deliveryMethod === "address" ? order.street : null,
        order.zip,
        order.city,
        order.country,
      ),
      "cac:PaymentMeans": paymentMeans(seller, "Überweisung"),
      "cac:TaxTotal": taxTotal(rateGroups),
      "cac:LegalMonetaryTotal": {
        ...amt("cbc:LineExtensionAmount", totalNet),
        ...amt("cbc:TaxExclusiveAmount", totalNet),
        ...amt("cbc:TaxInclusiveAmount", totalNet + totalTax),
        ...amt("cbc:PayableAmount", grandTotal),
      } as unknown as UblInvoice["cac:LegalMonetaryTotal"],
      "cac:InvoiceLine": invoiceLines(lines.map(({ item, effectiveQuantity }) => ({ ...item, quantity: effectiveQuantity }))),
    },
  };
}