#include "md5_digest.h"

// based heavily on this implementation:
// http://www.fourmilab.ch/md5/

#ifndef HIGHFIRST
#define byteReverse(buf, len) /* Nothing */
#else
/*
 * Note: this code is harmless on little-endian machines.
 */
static void byteReverse(unsigned char* buf, unsigned longs)
{
  u32 t;
  do
  {
    t = (u32)((unsigned)buf[3] << 8 | buf[2]) << 16 | ((unsigned)buf[1] << 8 | buf[0]);
    *(u32*)buf = t;
    buf += 4;
  } while (--longs);
}
#endif

/* The four core functions - F1 is optimized somewhat */

/* #define F1(x, y, z) (x & y | ~x & z) */
#define F1(x, y, z) (z ^ (x & (y ^ z)))
#define F2(x, y, z) F1(z, x, y)
#define F3(x, y, z) (x ^ y ^ z)
#define F4(x, y, z) (y ^ (x | ~z))

/* This is the central step in the MD5 algorithm. */
#define MD5STEP(f, w, x, y, z, data, s) (w += f(x, y, z) + data, w = w << s | w >> (32 - s), w += x)

/*
 * The core of the MD5 algorithm, this alters an existing MD5 hash to
 * reflect the addition of 16 longwords of new data.  MD5Update blocks
 * the data and converts bytes into longwords for this routine.
 */
static void MD5Transform(u32 buf[4], u32 in[16])
{
  // register u32 a, b, c, d;
  u32 a, b, c, d;

  a = buf[0];
  b = buf[1];
  c = buf[2];
  d = buf[3];

  MD5STEP(F1, a, b, c, d, in[0] + 0xd76aa478, 7);
  MD5STEP(F1, d, a, b, c, in[1] + 0xe8c7b756, 12);
  MD5STEP(F1, c, d, a, b, in[2] + 0x242070db, 17);
  MD5STEP(F1, b, c, d, a, in[3] + 0xc1bdceee, 22);
  MD5STEP(F1, a, b, c, d, in[4] + 0xf57c0faf, 7);
  MD5STEP(F1, d, a, b, c, in[5] + 0x4787c62a, 12);
  MD5STEP(F1, c, d, a, b, in[6] + 0xa8304613, 17);
  MD5STEP(F1, b, c, d, a, in[7] + 0xfd469501, 22);
  MD5STEP(F1, a, b, c, d, in[8] + 0x698098d8, 7);
  MD5STEP(F1, d, a, b, c, in[9] + 0x8b44f7af, 12);
  MD5STEP(F1, c, d, a, b, in[10] + 0xffff5bb1, 17);
  MD5STEP(F1, b, c, d, a, in[11] + 0x895cd7be, 22);
  MD5STEP(F1, a, b, c, d, in[12] + 0x6b901122, 7);
  MD5STEP(F1, d, a, b, c, in[13] + 0xfd987193, 12);
  MD5STEP(F1, c, d, a, b, in[14] + 0xa679438e, 17);
  MD5STEP(F1, b, c, d, a, in[15] + 0x49b40821, 22);

  MD5STEP(F2, a, b, c, d, in[1] + 0xf61e2562, 5);
  MD5STEP(F2, d, a, b, c, in[6] + 0xc040b340, 9);
  MD5STEP(F2, c, d, a, b, in[11] + 0x265e5a51, 14);
  MD5STEP(F2, b, c, d, a, in[0] + 0xe9b6c7aa, 20);
  MD5STEP(F2, a, b, c, d, in[5] + 0xd62f105d, 5);
  MD5STEP(F2, d, a, b, c, in[10] + 0x02441453, 9);
  MD5STEP(F2, c, d, a, b, in[15] + 0xd8a1e681, 14);
  MD5STEP(F2, b, c, d, a, in[4] + 0xe7d3fbc8, 20);
  MD5STEP(F2, a, b, c, d, in[9] + 0x21e1cde6, 5);
  MD5STEP(F2, d, a, b, c, in[14] + 0xc33707d6, 9);
  MD5STEP(F2, c, d, a, b, in[3] + 0xf4d50d87, 14);
  MD5STEP(F2, b, c, d, a, in[8] + 0x455a14ed, 20);
  MD5STEP(F2, a, b, c, d, in[13] + 0xa9e3e905, 5);
  MD5STEP(F2, d, a, b, c, in[2] + 0xfcefa3f8, 9);
  MD5STEP(F2, c, d, a, b, in[7] + 0x676f02d9, 14);
  MD5STEP(F2, b, c, d, a, in[12] + 0x8d2a4c8a, 20);

  MD5STEP(F3, a, b, c, d, in[5] + 0xfffa3942, 4);
  MD5STEP(F3, d, a, b, c, in[8] + 0x8771f681, 11);
  MD5STEP(F3, c, d, a, b, in[11] + 0x6d9d6122, 16);
  MD5STEP(F3, b, c, d, a, in[14] + 0xfde5380c, 23);
  MD5STEP(F3, a, b, c, d, in[1] + 0xa4beea44, 4);
  MD5STEP(F3, d, a, b, c, in[4] + 0x4bdecfa9, 11);
  MD5STEP(F3, c, d, a, b, in[7] + 0xf6bb4b60, 16);
  MD5STEP(F3, b, c, d, a, in[10] + 0xbebfbc70, 23);
  MD5STEP(F3, a, b, c, d, in[13] + 0x289b7ec6, 4);
  MD5STEP(F3, d, a, b, c, in[0] + 0xeaa127fa, 11);
  MD5STEP(F3, c, d, a, b, in[3] + 0xd4ef3085, 16);
  MD5STEP(F3, b, c, d, a, in[6] + 0x04881d05, 23);
  MD5STEP(F3, a, b, c, d, in[9] + 0xd9d4d039, 4);
  MD5STEP(F3, d, a, b, c, in[12] + 0xe6db99e5, 11);
  MD5STEP(F3, c, d, a, b, in[15] + 0x1fa27cf8, 16);
  MD5STEP(F3, b, c, d, a, in[2] + 0xc4ac5665, 23);

  MD5STEP(F4, a, b, c, d, in[0] + 0xf4292244, 6);
  MD5STEP(F4, d, a, b, c, in[7] + 0x432aff97, 10);
  MD5STEP(F4, c, d, a, b, in[14] + 0xab9423a7, 15);
  MD5STEP(F4, b, c, d, a, in[5] + 0xfc93a039, 21);
  MD5STEP(F4, a, b, c, d, in[12] + 0x655b59c3, 6);
  MD5STEP(F4, d, a, b, c, in[3] + 0x8f0ccc92, 10);
  MD5STEP(F4, c, d, a, b, in[10] + 0xffeff47d, 15);
  MD5STEP(F4, b, c, d, a, in[1] + 0x85845dd1, 21);
  MD5STEP(F4, a, b, c, d, in[8] + 0x6fa87e4f, 6);
  MD5STEP(F4, d, a, b, c, in[15] + 0xfe2ce6e0, 10);
  MD5STEP(F4, c, d, a, b, in[6] + 0xa3014314, 15);
  MD5STEP(F4, b, c, d, a, in[13] + 0x4e0811a1, 21);
  MD5STEP(F4, a, b, c, d, in[4] + 0xf7537e82, 6);
  MD5STEP(F4, d, a, b, c, in[11] + 0xbd3af235, 10);
  MD5STEP(F4, c, d, a, b, in[2] + 0x2ad7d2bb, 15);
  MD5STEP(F4, b, c, d, a, in[9] + 0xeb86d391, 21);

  buf[0] += a;
  buf[1] += b;
  buf[2] += c;
  buf[3] += d;
}

MD5Digest::MD5Digest()
{
  Reset();
}

void MD5Digest::Reset()
{
  this->buf[0] = 0x67452301;
  this->buf[1] = 0xefcdab89;
  this->buf[2] = 0x98badcfe;
  this->buf[3] = 0x10325476;

  this->bits[0] = 0;
  this->bits[1] = 0;
}

std::array<u8, MD5Digest::DIGEST_SIZE> MD5Digest::HashData(std::span<const u8> data)
{
  std::array<u8, DIGEST_SIZE> ret;

  MD5Digest digest;
  digest.Update(data);
  digest.Final(ret);
  return ret;
}

void MD5Digest::Update(const void* pData, u32 cbData)
{
  u32 t;
  const u8* pByteData = reinterpret_cast<const u8*>(pData);

  /* Update bitcount */

  t = this->bits[0];
  if ((this->bits[0] = t + ((u32)cbData << 3)) < t)
    this->bits[1]++; /* Carry from low to high */
  this->bits[1] += cbData >> 29;

  t = (t >> 3) & 0x3f; /* Bytes already in shsInfo->data */

  /* Handle any leading odd-sized chunks */

  if (t)
  {
    u8* p = (u8*)this->in + t;

    t = 64 - t;
    if (cbData < t)
    {
      std::memcpy(p, pByteData, cbData);
      return;
    }
    std::memcpy(p, pByteData, t);
    byteReverse(this->in, 16);
    MD5Transform(this->buf, (u32*)this->in);
    pByteData += t;
    cbData -= t;
  }
  /* Process data in 64-byte chunks */

  while (cbData >= 64)
  {
    std::memcpy(this->in, pByteData, 64);
    byteReverse(this->in, 16);
    MD5Transform(this->buf, (u32*)this->in);
    pByteData += 64;
    cbData -= 64;
  }

  /* Handle any remaining bytes of data. */

  std::memcpy(this->in, pByteData, cbData);
}

void MD5Digest::Update(std::span<const u8> data)
{
  if (!data.empty())
    Update(data.data(), static_cast<u32>(data.size_bytes()));
}

void MD5Digest::Final(std::span<u8, DIGEST_SIZE> digest)
{
  u32 count;
  u8* p;

  /* Compute number of bytes mod 64 */
  count = (this->bits[0] >> 3) & 0x3F;

  /* Set the first char of padding to 0x80.  This is safe since there is
     always at least one byte free */
  p = this->in + count;
  *p++ = 0x80;

  /* Bytes of padding needed to make 64 bytes */
  count = 64 - 1 - count;

  /* Pad out to 56 mod 64 */
  if (count < 8)
  {
    /* Two lots of padding:  Pad the first block to 64 bytes */
    std::memset(p, 0, count);
    byteReverse(this->in, 16);
    MD5Transform(this->buf, (u32*)this->in);

    /* Now fill the next block with 56 bytes */
    std::memset(this->in, 0, 56);
  }
  else
  {
    /* Pad block to 56 bytes */
    std::memset(p, 0, count - 8);
  }
  byteReverse(this->in, 14);

  /* Append length in bits and transform */
  ((u32*)this->in)[14] = this->bits[0];
  ((u32*)this->in)[15] = this->bits[1];

  MD5Transform(this->buf, (u32*)this->in);
  byteReverse((unsigned char*)this->buf, 4);
  std::memcpy(digest.data(), this->buf, 16);
}
