/**
 * Copyright since 2025 Mifos Initiative
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/**
 * The comparable fingerprint of an Aadhaar number: SHA-256 of the 12 digits, as 64 lowercase hex characters.
 *
 * Only this fingerprint is sent to the server. The KYC create/update calls are recorded in an audit table and a log
 * on the server, so the 12-digit number must not be in the request.
 *
 * A plain, unkeyed SHA-256 of 12 digits can be reversed by trying every number, so this is a lookup key and not
 * protection against someone who can read the stored value.
 *
 * Written out in full instead of using `crypto.subtle` because that API is asynchronous and only exists in secure
 * contexts, while the callers (a form-value getter, a blur handler) need the answer synchronously and the app may be
 * served over plain HTTP.
 */

const K = [
  0x428a2f98,
  0x71374491,
  0xb5c0fbcf,
  0xe9b5dba5,
  0x3956c25b,
  0x59f111f1,
  0x923f82a4,
  0xab1c5ed5,
  0xd807aa98,
  0x12835b01,
  0x243185be,
  0x550c7dc3,
  0x72be5d74,
  0x80deb1fe,
  0x9bdc06a7,
  0xc19bf174,
  0xe49b69c1,
  0xefbe4786,
  0x0fc19dc6,
  0x240ca1cc,
  0x2de92c6f,
  0x4a7484aa,
  0x5cb0a9dc,
  0x76f988da,
  0x983e5152,
  0xa831c66d,
  0xb00327c8,
  0xbf597fc7,
  0xc6e00bf3,
  0xd5a79147,
  0x06ca6351,
  0x14292967,
  0x27b70a85,
  0x2e1b2138,
  0x4d2c6dfc,
  0x53380d13,
  0x650a7354,
  0x766a0abb,
  0x81c2c92e,
  0x92722c85,
  0xa2bfe8a1,
  0xa81a664b,
  0xc24b8b70,
  0xc76c51a3,
  0xd192e819,
  0xd6990624,
  0xf40e3585,
  0x106aa070,
  0x19a4c116,
  0x1e376c08,
  0x2748774c,
  0x34b0bcb5,
  0x391c0cb3,
  0x4ed8aa4a,
  0x5b9cca4f,
  0x682e6ff3,
  0x748f82ee,
  0x78a5636f,
  0x84c87814,
  0x8cc70208,
  0x90befffa,
  0xa4506ceb,
  0xbef9a3f7,
  0xc67178f2
];

function rotr(x: number, n: number): number {
  return (x >>> n) | (x << (32 - n));
}

/** SHA-256 of a string (UTF-8 encoded), as lowercase hex. */
export function sha256Hex(text: string): string {
  const bytes: number[] = [];
  for (const ch of unescape(encodeURIComponent(text))) {
    bytes.push(ch.charCodeAt(0));
  }
  const bitLength = bytes.length * 8;

  bytes.push(0x80);
  while (bytes.length % 64 !== 56) {
    bytes.push(0);
  }
  // 64-bit big-endian message length; inputs here are tiny so the high word is always 0.
  const high = Math.floor(bitLength / 0x100000000);
  const low = bitLength >>> 0;
  for (const word of [
    high,
    low
  ]) {
    bytes.push((word >>> 24) & 0xff, (word >>> 16) & 0xff, (word >>> 8) & 0xff, word & 0xff);
  }

  const h = [
    0x6a09e667,
    0xbb67ae85,
    0x3c6ef372,
    0xa54ff53a,
    0x510e527f,
    0x9b05688c,
    0x1f83d9ab,
    0x5be0cd19
  ];
  const w = new Array<number>(64);

  for (let offset = 0; offset < bytes.length; offset += 64) {
    for (let i = 0; i < 16; i++) {
      const j = offset + i * 4;
      w[i] = (bytes[j] << 24) | (bytes[j + 1] << 16) | (bytes[j + 2] << 8) | bytes[j + 3];
    }
    for (let i = 16; i < 64; i++) {
      const s0 = rotr(w[i - 15], 7) ^ rotr(w[i - 15], 18) ^ (w[i - 15] >>> 3);
      const s1 = rotr(w[i - 2], 17) ^ rotr(w[i - 2], 19) ^ (w[i - 2] >>> 10);
      w[i] = (w[i - 16] + s0 + w[i - 7] + s1) | 0;
    }

    let [
      a,
      b,
      c,
      d,
      e,
      f,
      g,
      hh
    ] = h;
    for (let i = 0; i < 64; i++) {
      const S1 = rotr(e, 6) ^ rotr(e, 11) ^ rotr(e, 25);
      const ch = (e & f) ^ (~e & g);
      const t1 = (hh + S1 + ch + K[i] + w[i]) | 0;
      const S0 = rotr(a, 2) ^ rotr(a, 13) ^ rotr(a, 22);
      const maj = (a & b) ^ (a & c) ^ (b & c);
      const t2 = (S0 + maj) | 0;
      hh = g;
      g = f;
      f = e;
      e = (d + t1) | 0;
      d = c;
      c = b;
      b = a;
      a = (t1 + t2) | 0;
    }
    h[0] = (h[0] + a) | 0;
    h[1] = (h[1] + b) | 0;
    h[2] = (h[2] + c) | 0;
    h[3] = (h[3] + d) | 0;
    h[4] = (h[4] + e) | 0;
    h[5] = (h[5] + f) | 0;
    h[6] = (h[6] + g) | 0;
    h[7] = (h[7] + hh) | 0;
  }

  return h.map((x) => (x >>> 0).toString(16).padStart(8, '0')).join('');
}

/**
 * The fingerprint for a 12-digit Aadhaar, or null when the value is not one (too short, masked, a placeholder).
 * Spaces and hyphens people type between the groups are ignored.
 */
export function aadhaarHash(aadhaar: string | null | undefined): string | null {
  const digits = (aadhaar ?? '').replace(/[\s-]/g, '');
  return /^\d{12}$/.test(digits) ? sha256Hex(digits) : null;
}