/**
 * 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,
  });
}