const SHA256_CONSTANTS = new Uint32Array([
  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 rotateRight(value: number, bits: number): number {
  return (value >>> bits) | (value << (32 - bits));
}

function processBlock(
  bytes: Uint8Array,
  offset: number,
  state: Uint32Array,
  words: Uint32Array,
): void {
  for (let index = 0; index < 16; index += 1) {
    const wordOffset = offset + index * 4;
    words[index] = (
      (bytes[wordOffset]! << 24) |
      (bytes[wordOffset + 1]! << 16) |
      (bytes[wordOffset + 2]! << 8) |
      bytes[wordOffset + 3]!
    ) >>> 0;
  }

  for (let index = 16; index < 64; index += 1) {
    const previous15 = words[index - 15]!;
    const previous2 = words[index - 2]!;
    const sigma0 =
      rotateRight(previous15, 7) ^
      rotateRight(previous15, 18) ^
      (previous15 >>> 3);
    const sigma1 =
      rotateRight(previous2, 17) ^
      rotateRight(previous2, 19) ^
      (previous2 >>> 10);
    words[index] = (
      words[index - 16]! +
      sigma0 +
      words[index - 7]! +
      sigma1
    ) >>> 0;
  }

  let a = state[0]!;
  let b = state[1]!;
  let c = state[2]!;
  let d = state[3]!;
  let e = state[4]!;
  let f = state[5]!;
  let g = state[6]!;
  let h = state[7]!;

  for (let index = 0; index < 64; index += 1) {
    const sum1 = rotateRight(e, 6) ^ rotateRight(e, 11) ^ rotateRight(e, 25);
    const choice = (e & f) ^ (~e & g);
    const temporary1 = (
      h +
      sum1 +
      choice +
      SHA256_CONSTANTS[index]! +
      words[index]!
    ) >>> 0;
    const sum0 = rotateRight(a, 2) ^ rotateRight(a, 13) ^ rotateRight(a, 22);
    const majority = (a & b) ^ (a & c) ^ (b & c);
    const temporary2 = (sum0 + majority) >>> 0;

    h = g;
    g = f;
    f = e;
    e = (d + temporary1) >>> 0;
    d = c;
    c = b;
    b = a;
    a = (temporary1 + temporary2) >>> 0;
  }

  state[0] = (state[0]! + a) >>> 0;
  state[1] = (state[1]! + b) >>> 0;
  state[2] = (state[2]! + c) >>> 0;
  state[3] = (state[3]! + d) >>> 0;
  state[4] = (state[4]! + e) >>> 0;
  state[5] = (state[5]! + f) >>> 0;
  state[6] = (state[6]! + g) >>> 0;
  state[7] = (state[7]! + h) >>> 0;
}

export function sha256(bytes: Uint8Array): Uint8Array {
  const state = new Uint32Array([
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
    0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
  ]);
  const words = new Uint32Array(64);
  const completeBytes = bytes.byteLength - (bytes.byteLength % 64);

  for (let offset = 0; offset < completeBytes; offset += 64) {
    processBlock(bytes, offset, state, words);
  }

  const remainder = bytes.byteLength - completeBytes;
  const tailLength = remainder < 56 ? 64 : 128;
  const tail = new Uint8Array(tailLength);
  tail.set(bytes.subarray(completeBytes));
  tail[remainder] = 0x80;
  new DataView(tail.buffer).setBigUint64(
    tailLength - 8,
    BigInt(bytes.byteLength) * 8n,
    false,
  );

  for (let offset = 0; offset < tailLength; offset += 64) {
    processBlock(tail, offset, state, words);
  }

  const digest = new Uint8Array(32);
  const digestView = new DataView(digest.buffer);
  for (let index = 0; index < state.length; index += 1) {
    digestView.setUint32(index * 4, state[index]!, false);
  }
  return digest;
}

export function bytesToHex(bytes: Uint8Array): string {
  let result = "";
  for (const byte of bytes) {
    result += byte.toString(16).padStart(2, "0");
  }
  return result;
}