/**
 * PlusFit24 – IBAN Validierung
 * Prüft: Format, Ländercode, Länge, Prüfziffer (Modulo 97)
 */

const IBAN_LENGTHS = {
  AL:28, AD:24, AT:20, AZ:28, BH:22, BE:16, BA:20, BR:29, BG:22,
  CR:22, HR:21, CY:28, CZ:24, DK:18, DO:28, EE:20, FO:18, FI:18,
  FR:27, GE:22, DE:22, GI:23, GL:18, GT:28, HU:28, IS:26, IE:22,
  IL:23, IT:27, JO:30, KZ:20, KW:30, LV:21, LB:28, LI:21, LT:20,
  LU:20, MK:19, MT:31, MR:27, MU:30, MC:27, MD:24, ME:22, NL:18,
  NO:15, PK:24, PS:29, PL:28, PT:25, QA:29, RO:24, SM:27, SA:24,
  RS:22, SK:24, SI:19, ES:24, SE:24, CH:21, TN:24, TR:26, AE:23,
  GB:22, VG:24
};

function formatIBAN(value) {
  const clean = value.replace(/[^A-Z0-9]/gi, '').toUpperCase();
  return clean.replace(/(.{4})/g, '$1 ').trim();
}

function validateIBAN(iban) {
  const clean = iban.replace(/\s/g, '').toUpperCase();

  if (clean.length < 5) return { valid: false, error: 'IBAN zu kurz' };

  const country = clean.substring(0, 2);
  if (!/^[A-Z]{2}$/.test(country)) return { valid: false, error: 'Ungültiger Ländercode' };

  const checkDigits = clean.substring(2, 4);
  if (!/^\d{2}$/.test(checkDigits)) return { valid: false, error: 'Prüfziffern ungültig' };

  const expectedLength = IBAN_LENGTHS[country];
  if (!expectedLength) return { valid: false, error: 'Ländercode "' + country + '" nicht unterstützt' };
  if (clean.length !== expectedLength) {
    return { valid: false, error: country + '-IBAN muss ' + expectedLength + ' Zeichen haben (aktuell: ' + clean.length + ')' };
  }

  if (!/^[A-Z0-9]+$/.test(clean.substring(4))) {
    return { valid: false, error: 'IBAN enthält ungültige Zeichen' };
  }

  // Modulo-97 Prüfung
  const rearranged = clean.substring(4) + clean.substring(0, 4);
  const numeric = rearranged.split('').map(c => {
    const code = c.charCodeAt(0);
    return code >= 65 ? (code - 55).toString() : c;
  }).join('');

  let remainder = 0;
  for (let i = 0; i < numeric.length; i++) {
    remainder = (remainder * 10 + parseInt(numeric[i])) % 97;
  }

  if (remainder !== 1) return { valid: false, error: 'Prüfziffer falsch – IBAN ungültig' };

  return { valid: true, formatted: formatIBAN(clean) };
}

function attachIBANValidation(inputEl, statusEl, messageEl) {
  inputEl.addEventListener('input', function () {
    const rawClean = this.value.replace(/[^A-Z0-9]/gi, '').toUpperCase();
    this.value = formatIBAN(rawClean);

    if (rawClean.length < 5) {
      if (statusEl) statusEl.textContent = '';
      if (messageEl) { messageEl.textContent = ''; messageEl.className = 'iban-message'; }
      this.classList.remove('input-error', 'input-valid');
      return;
    }

    const result = validateIBAN(rawClean);
    if (result.valid) {
      if (statusEl) statusEl.textContent = '✅';
      if (messageEl) { messageEl.textContent = 'IBAN gültig'; messageEl.className = 'iban-message success'; }
      this.classList.remove('input-error'); this.classList.add('input-valid');
    } else {
      if (statusEl) statusEl.textContent = '❌';
      if (messageEl) { messageEl.textContent = result.error; messageEl.className = 'iban-message error'; }
      this.classList.remove('input-valid'); this.classList.add('input-error');
    }
  });
}