stellarAddress.ts

/**
 * Lightweight Stellar address validation for display and form handling.
 *
 * Validation runs in two stages so that the expensive work only runs on
 * inputs that have already passed basic structural checks:
 *
 * 1. Fast structural guard: length, prefix, and the Stellar base32 alphabet.
 * 2. StrKey checksum verification: base32 decode the payload, confirm the
 *    ed25519 public-key version byte (0x30), and verify the trailing
 *    CRC16-XModem checksum covers all preceding bytes.
 *
 * This prevents the function from accepting structurally valid but
 * semantically invalid strings while remaining self-contained (no
 * Stellar SDK dependency).
 */

const STELLAR_PUBLIC_KEY_LENGTH = 56;
const STELLAR_PUBLIC_KEY_PATTERN = /^G[A-Z2-7]{55}$/;

const STELLAR_BASE32_ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';

const STELLAR_PUBLIC_KEY_VERSION_BYTE = 0x30;

const CRC16_XMODEM_TABLE: readonly number[] = [
  0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
  0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
  0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
  0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
  0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
  0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
  0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
  0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
  0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
  0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
  0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
  0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
  0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
  0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
  0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
  0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
  0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
  0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
  0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
  0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
  0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
  0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
  0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
  0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
  0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
  0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
  0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
  0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
  0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
  0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
  0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
  0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0,
];

/**
 * Computes the CRC16-XModem checksum over the provided payload.
 *
 * This matches the Stellar's `calculateChecksum` implementation, which stores
 * the resulting value in little-endian byte order in the encoded key.
 */
function computeCRC16XModem(payload: Uint8Array): number {
  let crc = 0x0000;
  for (let i = 0; i < payload.length; i++) {
    const lookupIndex = (crc >> 8) ^ payload[i];
    crc = (crc << 8) ^ CRC16_XMODEM_TABLE[lookupIndex];
    crc &= 0xffff;
  }
  return crc;
}

/**
 * Decodes a Stellar base32 string using the Stellar alphabet (A-Z and 2-7)
 * into a Uint8Array.
 *
 * Returns `null` if the input contains characters outside the alphabet or
 * if the bit alignment is wrong, ensuring callers never receive partial
 * or malformed results.
 */
function decodeStellarBase32(encoded: string): Uint8Array | null {
  const bytes: number[] = [];
  let bits = 0;
  let val = 0;

  for (let i = 0; i < encoded.length; i++) {
    const idx = STELLAR_BASE32_ALPHABET.indexOf(encoded[i]);
    if (idx === -1) {
      return null;
    }
    val = (val << 5) | idx;
    bits += 5;

    if (bits >= 8) {
      bits -= 8;
      bytes.push((val >>> bits) & 0xff);
    }
  }

  return new Uint8Array(bytes);
}

/**
 * Verifies the StrKey checksum for an ed25519 Stellar public key.
 *
 * The checksum covers the version byte plus the 32-byte public key payload.
 * The stored CRC is read in little-endian order to match the Stellar
 * base32 encoding.
 */
function isValidStellarChecksum(address: string): boolean {
  const decoded = decodeStellarBase32(address);
  if (!decoded || decoded.length !== 35) {
    return false;
  }

  if (decoded[0] !== STELLAR_PUBLIC_KEY_VERSION_BYTE) {
    return false;
  }

  const payload = decoded.slice(0, -2);
  const storedCRC = decoded[decoded.length - 2] | (decoded[decoded.length - 1] << 8);
  const computedCRC = computeCRC16XModem(payload);

  return storedCRC === computedCRC;
}

export function isValidStellarAddress(value: string | null | undefined): boolean {
  if (typeof value !== 'string') {
    return false;
  }

  const normalizedValue = normalizeStellarAddress(value);
  if (!normalizedValue) {
    return false;
  }

  if (
    normalizedValue.length !== STELLAR_PUBLIC_KEY_LENGTH ||
    !STELLAR_PUBLIC_KEY_PATTERN.test(normalizedValue)
  ) {
    return false;
  }

  return isValidStellarChecksum(normalizedValue);
}

/**
 * Normalize a Stellar address string.
 *
 * This function trims surrounding whitespace and converts the value to
 * upper‑case. It never throws – non‑string inputs result in an empty string.
 *
 * @param value The raw address string (or `null`/`undefined`).
 * @returns The normalized address, or an empty string for invalid input.
 */
export function normalizeStellarAddress(value: string | null | undefined): string {
  if (typeof value !== 'string') {
    return '';
  }

  return value.trim().toUpperCase();
}