first version

app/services/invoice/validation.ts

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+// IBAN validation helpers (BBAN length per country + mod-97 checksum).
+// Deliberately self-contained — avoids pulling in an extra dependency.
+
+const IBAN_LENGTHS: Record<string, number> = {
+  AD: 24, AE: 23, AL: 28, AT: 20, AZ: 28, BA: 20, BE: 16, BG: 22, BH: 22,
+  BR: 29, BY: 28, CH: 21, CR: 22, CY: 28, CZ: 24, DE: 22, DK: 18, DO: 28,
+  EE: 20, EG: 29, ES: 24, FI: 18, FO: 18, FR: 27, GB: 22, GE: 22, GI: 23,
+  GL: 18, GR: 27, GT: 28, HR: 21, HU: 28, IE: 22, IL: 23, IQ: 23, IS: 26,
+  IT: 27, JO: 30, KW: 30, KZ: 20, LB: 28, LC: 32, LI: 21, LT: 20, LU: 20,
+  LV: 21, LY: 25, MC: 27, MD: 24, ME: 22, MK: 19, MR: 27, MT: 31, MU: 30,
+  NL: 18, NO: 15, PK: 24, PL: 28, PS: 29, PT: 25, QA: 29, RO: 24, RS: 22,
+  SA: 24, SC: 31, SE: 24, SI: 19, SK: 24, SM: 27, ST: 25, SV: 28, TL: 23,
+  TN: 24, TR: 26, UA: 29, VA: 22, VG: 24, XK: 20,
+};
+
+/** Strips spaces and uppercases. Returns "" if input is null-ish. */
+export function normaliseIban(value: string | null | undefined): string {
+  return (value ?? "").replace(/\s+/g, "").toUpperCase();
+}
+
+/** Formats an IBAN in the canonical 4-char-grouped form. */
+export function formatIban(value: string): string {
+  const n = normaliseIban(value);
+  return n.replace(/(.{4})/g, "$1 ").trim();
+}
+
+/** Validates IBAN: country length + mod-97 checksum. */
+export function isValidIban(value: string): boolean {
+  const iban = normaliseIban(value);
+  if (!/^[A-Z]{2}\d{2}[A-Z0-9]+$/.test(iban)) return false;
+  const country = iban.slice(0, 2);
+  const expectedLength = IBAN_LENGTHS[country];
+  if (!expectedLength || iban.length !== expectedLength) return false;
+
+  // Move first 4 chars to the end, convert letters to digits (A=10..Z=35).
+  const rearranged = iban.slice(4) + iban.slice(0, 4);
+  let numeric = "";
+  for (const ch of rearranged) {
+    if (ch >= "0" && ch <= "9") numeric += ch;
+    else numeric += (ch.charCodeAt(0) - 55).toString(); // 'A' (65) -> 10
+  }
+  // mod 97 over a long numeric string — chunked to fit safely in JS numbers.
+  let remainder = 0;
+  for (let i = 0; i < numeric.length; i += 7) {
+    const block = remainder.toString() + numeric.substring(i, i + 7);
+    remainder = parseInt(block, 10) % 97;
+  }
+  return remainder === 1;
+}
+
+/** True for BIC formats: 8 or 11 alphanumeric uppercase characters. */
+export function isValidBic(value: string): boolean {
+  const v = (value ?? "").replace(/\s+/g, "").toUpperCase();
+  return /^[A-Z]{6}[A-Z0-9]{2}([A-Z0-9]{3})?$/.test(v);
+}
+
+/** Austrian UID: ATU followed by 8 digits (case-insensitive). */
+export function isValidAtVatId(value: string): boolean {
+  const v = (value ?? "").replace(/\s+/g, "").toUpperCase();
+  return /^ATU\d{8}$/.test(v);
+}