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app/services/invoice/girocode.ts

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+/**
+ * EPC (SEPA Credit Transfer) QR code payload, a.k.a. GiroCode.
+ * Specification: EPC069-12 v3.0.
+ *
+ * The payload is a fixed-order line-delimited block of fields that any SEPA
+ * banking app can scan to pre-fill a transfer.
+ */
+
+import QRCode from "qrcode";
+
+export interface GiroCodeInput {
+  beneficiaryName: string;
+  iban: string;
+  bic?: string;
+  amount: number;
+  currency?: string;
+  /** Free-form remittance information (e.g. invoice number). Max 140 chars. */
+  remittance: string;
+}
+
+export function buildGiroCodePayload(input: GiroCodeInput): string {
+  const currency = input.currency || "EUR";
+  if (currency !== "EUR") {
+    // EPC069-12 requires EUR; keep going but warn (most invoices are EUR).
+    console.warn(`GiroCode: non-EUR currency ${currency} is non-standard.`);
+  }
+
+  // Beneficiary name max 70 chars per spec.
+  const name = input.beneficiaryName.slice(0, 70);
+  const iban = input.iban.replace(/\s+/g, "").toUpperCase();
+  const bic = (input.bic || "").replace(/\s+/g, "").toUpperCase();
+  const amount = input.amount.toFixed(2);
+  const remittance = input.remittance.slice(0, 140);
+
+  // Field order is fixed; trailing fields can be empty.
+  // Service tag SCT = SEPA Credit Transfer.
+  const lines = [
+    "BCD",
+    "002",          // version
+    "1",            // character set 1 = UTF-8
+    "SCT",          // SEPA Credit Transfer
+    bic,            // BIC (optional in v002)
+    name,
+    iban,
+    `EUR${amount}`,
+    "",             // purpose (optional)
+    "",             // structured remittance
+    remittance,     // unstructured remittance
+  ];
+  return lines.join("\n");
+}
+
+export async function buildGiroCodeDataUrl(
+  input: GiroCodeInput,
+): Promise<string> {
+  const payload = buildGiroCodePayload(input);
+  // EPC requires error correction level M.
+  return QRCode.toDataURL(payload, {
+    errorCorrectionLevel: "M",
+    margin: 1,
+    width: 256,
+  });
+}