// SPDX-FileCopyrightText: 2019-2024 Connor McLaughlin <stenzek@gmail.com>
// SPDX-License-Identifier: CC-BY-NC-ND-4.0

// Based on https://github.com/B-Con/crypto-algorithms/blob/master/sha256.c
// By Brad Conte (brad AT bradconte.com)

#include "sha256_digest.h"
#include "string_util.h"

#include <cstring>

SHA256Digest::SHA256Digest()
{
  Reset();
}

std::string SHA256Digest::DigestToString(const std::span<const u8, DIGEST_SIZE> digest)
{
  return StringUtil::EncodeHex<u8>(digest);
}

SHA256Digest::Digest SHA256Digest::GetDigest(const void* data, size_t len)
{
  Digest ret;
  SHA256Digest digest;
  digest.Update(data, len);
  digest.Final(ret);
  return ret;
}

SHA256Digest::Digest SHA256Digest::GetDigest(std::span<const u8> data)
{
  Digest ret;
  SHA256Digest digest;
  digest.Update(data);
  digest.Final(ret);
  return ret;
}

#define ROTLEFT(a, b) (((a) << (b)) | ((a) >> (32 - (b))))
#define ROTRIGHT(a, b) (((a) >> (b)) | ((a) << (32 - (b))))

#define CH(x, y, z) (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x, y, z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EP0(x) (ROTRIGHT(x, 2) ^ ROTRIGHT(x, 13) ^ ROTRIGHT(x, 22))
#define EP1(x) (ROTRIGHT(x, 6) ^ ROTRIGHT(x, 11) ^ ROTRIGHT(x, 25))
#define SIG0(x) (ROTRIGHT(x, 7) ^ ROTRIGHT(x, 18) ^ ((x) >> 3))
#define SIG1(x) (ROTRIGHT(x, 17) ^ ROTRIGHT(x, 19) ^ ((x) >> 10))

static constexpr std::array<u32, 64> 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}};

void SHA256Digest::TransformBlock()
{
  std::array<u32, 64> m;

  size_t i = 0;
  for (size_t j = 0; i < 16; ++i, j += 4)
    m[i] = (m_block[j] << 24) | (m_block[j + 1] << 16) | (m_block[j + 2] << 8) | (m_block[j + 3]);
  for (; i < 64; ++i)
    m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];

  u32 a = m_state[0];
  u32 b = m_state[1];
  u32 c = m_state[2];
  u32 d = m_state[3];
  u32 e = m_state[4];
  u32 f = m_state[5];
  u32 g = m_state[6];
  u32 h = m_state[7];

  for (i = 0; i < 64; ++i)
  {
    u32 t1 = h + EP1(e) + CH(e, f, g) + k[i] + m[i];
    u32 t2 = EP0(a) + MAJ(a, b, c);
    h = g;
    g = f;
    f = e;
    e = d + t1;
    d = c;
    c = b;
    b = a;
    a = t1 + t2;
  }

  m_state[0] += a;
  m_state[1] += b;
  m_state[2] += c;
  m_state[3] += d;
  m_state[4] += e;
  m_state[5] += f;
  m_state[6] += g;
  m_state[7] += h;
}

void SHA256Digest::Reset()
{
  m_block_length = 0;
  m_bit_length = 0;
  m_state[0] = 0x6a09e667;
  m_state[1] = 0xbb67ae85;
  m_state[2] = 0x3c6ef372;
  m_state[3] = 0xa54ff53a;
  m_state[4] = 0x510e527f;
  m_state[5] = 0x9b05688c;
  m_state[6] = 0x1f83d9ab;
  m_state[7] = 0x5be0cd19;
}

void SHA256Digest::Update(std::span<const u8> data)
{
  const size_t len = data.size();
  for (size_t pos = 0; pos < len;)
  {
    const u32 copy_len = static_cast<u32>(std::min<size_t>(len - pos, BLOCK_SIZE - m_block_length));
    std::memcpy(&m_block[m_block_length], &data[pos], copy_len);
    m_block_length += copy_len;
    pos += copy_len;

    if (m_block_length == BLOCK_SIZE)
    {
      TransformBlock();
      m_bit_length += 512;
      m_block_length = 0;
    }
  }
}

void SHA256Digest::Update(const void* data, size_t len)
{
  Update(std::span<const u8>(static_cast<const u8*>(data), len));
}

void SHA256Digest::Final(std::span<u8, DIGEST_SIZE> digest)
{
  // Pad whatever data is left in the buffer.
  if (m_block_length < 56)
  {
    size_t i = m_block_length;
    m_block[i++] = 0x80;
    while (i < 56)
      m_block[i++] = 0x00;
  }
  else
  {
    size_t i = m_block_length;
    m_block[i++] = 0x80;
    while (i < 64)
      m_block[i++] = 0x00;
    TransformBlock();
    m_block = {};
  }

  // Append to the padding the total message's length in bits and transform.
  m_bit_length += m_block_length * 8;
  m_block[63] = static_cast<u8>(m_bit_length);
  m_block[62] = static_cast<u8>(m_bit_length >> 8);
  m_block[61] = static_cast<u8>(m_bit_length >> 16);
  m_block[60] = static_cast<u8>(m_bit_length >> 24);
  m_block[59] = static_cast<u8>(m_bit_length >> 32);
  m_block[58] = static_cast<u8>(m_bit_length >> 40);
  m_block[57] = static_cast<u8>(m_bit_length >> 48);
  m_block[56] = static_cast<u8>(m_bit_length >> 56);
  TransformBlock();

  // Since this implementation uses little endian byte ordering and SHA uses big endian,
  // reverse all the bytes when copying the final state to the output hash.
  for (size_t i = 0; i < 4; ++i)
  {
    digest[i] = (m_state[0] >> (24 - i * 8)) & 0x000000ff;
    digest[i + 4] = (m_state[1] >> (24 - i * 8)) & 0x000000ff;
    digest[i + 8] = (m_state[2] >> (24 - i * 8)) & 0x000000ff;
    digest[i + 12] = (m_state[3] >> (24 - i * 8)) & 0x000000ff;
    digest[i + 16] = (m_state[4] >> (24 - i * 8)) & 0x000000ff;
    digest[i + 20] = (m_state[5] >> (24 - i * 8)) & 0x000000ff;
    digest[i + 24] = (m_state[6] >> (24 - i * 8)) & 0x000000ff;
    digest[i + 28] = (m_state[7] >> (24 - i * 8)) & 0x000000ff;
  }
}

SHA256Digest::Digest SHA256Digest::Final()
{
  Digest ret;
  Final(ret);
  return ret;
}