/**
 * @file md5.cpp
 * @The implement of md5.
 * @author Jiewei Wei
 * @mail weijieweijerry@163.com
 * @github https://github.com/JieweiWei
 * @data Oct 19 2014
 *
 */

#include "md5.h"

/* Define the static member of MD5. */
const byte MD5::PADDING[64] = { 0x80 };
const char MD5::HEX_NUMBERS[16] = {
  '0', '1', '2', '3',
  '4', '5', '6', '7',
  '8', '9', 'a', 'b',
  'c', 'd', 'e', 'f'
};

/**
 * @Construct a MD5 object with a string.
 *
 * @param {message} the message will be transformed.
 *
 */
MD5::MD5(const string& message) {
  finished = false;
  /* Reset number of bits. */
  count[0] = count[1] = 0;
  /* Initialization constants. */
  state[0] = 0x67452301;
  state[1] = 0xefcdab89;
  state[2] = 0x98badcfe;
  state[3] = 0x10325476;

  /* Initialization the object according to message. */
  init((const byte*)message.c_str(), message.length());
}

/**
 * @Generate md5 digest.
 *
 * @return the message-digest.
 *
 */
const byte* MD5::getDigest() {
  if (!finished) {
    finished = true;

    byte bits[8];
    bit32 oldState[4];
    bit32 oldCount[2];
    bit32 index, padLen;

    /* Save current state and count. */
    memcpy(oldState, state, 16);
    memcpy(oldCount, count, 8);

    /* Save number of bits */
    encode(count, bits, 8);

    /* Pad out to 56 mod 64. */
    index = (bit32)((count[0] >> 3) & 0x3f);
    padLen = (index < 56) ? (56 - index) : (120 - index);
    init(PADDING, padLen);

    /* Append length (before padding) */
    init(bits, 8);

    /* Store state in digest */
    encode(state, digest, 16);

    /* Restore current state and count. */
    memcpy(state, oldState, 16);
    memcpy(count, oldCount, 8);
  }
  return digest;
}

/**
 * @Initialization the md5 object, processing another message block,
 * and updating the context.
 *
 * @param {input} the input message.
 *
 * @param {len} the number btye of message.
 *
 */
void MD5::init(const byte* input, size_t len) {

  bit32 i, index, partLen;

  finished = false;

  /* Compute number of bytes mod 64 */
  index = (bit32)((count[0] >> 3) & 0x3f);

  /* update number of bits */
  if ((count[0] += ((bit32)len << 3)) < ((bit32)len << 3)) {
    ++count[1];
  }
  count[1] += ((bit32)len >> 29);

  partLen = 64 - index;

  /* transform as many times as possible. */
  if (len >= partLen) {

    memcpy(&buffer[index], input, partLen);
    transform(buffer);

    for (i = partLen; i + 63 < len; i += 64) {
      transform(&input[i]);
    }
    index = 0;

  } else {
    i = 0;
  }

  /* Buffer remaining input */
  memcpy(&buffer[index], &input[i], len - i);
}

/**
 * @MD5 basic transformation. Transforms state based on block.
 *
 * @param {block} the message block.
 */
void MD5::transform(const byte block[64]) {

  bit32 a = state[0], b = state[1], c = state[2], d = state[3], x[16];

  decode(block, x, 64);

  /* Round 1 */
  FF (a, b, c, d, x[ 0], s11, 0xd76aa478);
  FF (d, a, b, c, x[ 1], s12, 0xe8c7b756);
  FF (c, d, a, b, x[ 2], s13, 0x242070db);
  FF (b, c, d, a, x[ 3], s14, 0xc1bdceee);
  FF (a, b, c, d, x[ 4], s11, 0xf57c0faf);
  FF (d, a, b, c, x[ 5], s12, 0x4787c62a);
  FF (c, d, a, b, x[ 6], s13, 0xa8304613);
  FF (b, c, d, a, x[ 7], s14, 0xfd469501);
  FF (a, b, c, d, x[ 8], s11, 0x698098d8);
  FF (d, a, b, c, x[ 9], s12, 0x8b44f7af);
  FF (c, d, a, b, x[10], s13, 0xffff5bb1);
  FF (b, c, d, a, x[11], s14, 0x895cd7be);
  FF (a, b, c, d, x[12], s11, 0x6b901122);
  FF (d, a, b, c, x[13], s12, 0xfd987193);
  FF (c, d, a, b, x[14], s13, 0xa679438e);
  FF (b, c, d, a, x[15], s14, 0x49b40821);

  /* Round 2 */
  GG (a, b, c, d, x[ 1], s21, 0xf61e2562);
  GG (d, a, b, c, x[ 6], s22, 0xc040b340);
  GG (c, d, a, b, x[11], s23, 0x265e5a51);
  GG (b, c, d, a, x[ 0], s24, 0xe9b6c7aa);
  GG (a, b, c, d, x[ 5], s21, 0xd62f105d);
  GG (d, a, b, c, x[10], s22,  0x2441453);
  GG (c, d, a, b, x[15], s23, 0xd8a1e681);
  GG (b, c, d, a, x[ 4], s24, 0xe7d3fbc8);
  GG (a, b, c, d, x[ 9], s21, 0x21e1cde6);
  GG (d, a, b, c, x[14], s22, 0xc33707d6);
  GG (c, d, a, b, x[ 3], s23, 0xf4d50d87);
  GG (b, c, d, a, x[ 8], s24, 0x455a14ed);
  GG (a, b, c, d, x[13], s21, 0xa9e3e905);
  GG (d, a, b, c, x[ 2], s22, 0xfcefa3f8);
  GG (c, d, a, b, x[ 7], s23, 0x676f02d9);
  GG (b, c, d, a, x[12], s24, 0x8d2a4c8a);

  /* Round 3 */
  HH (a, b, c, d, x[ 5], s31, 0xfffa3942);
  HH (d, a, b, c, x[ 8], s32, 0x8771f681);
  HH (c, d, a, b, x[11], s33, 0x6d9d6122);
  HH (b, c, d, a, x[14], s34, 0xfde5380c);
  HH (a, b, c, d, x[ 1], s31, 0xa4beea44);
  HH (d, a, b, c, x[ 4], s32, 0x4bdecfa9);
  HH (c, d, a, b, x[ 7], s33, 0xf6bb4b60);
  HH (b, c, d, a, x[10], s34, 0xbebfbc70);
  HH (a, b, c, d, x[13], s31, 0x289b7ec6);
  HH (d, a, b, c, x[ 0], s32, 0xeaa127fa);
  HH (c, d, a, b, x[ 3], s33, 0xd4ef3085);
  HH (b, c, d, a, x[ 6], s34,  0x4881d05);
  HH (a, b, c, d, x[ 9], s31, 0xd9d4d039);
  HH (d, a, b, c, x[12], s32, 0xe6db99e5);
  HH (c, d, a, b, x[15], s33, 0x1fa27cf8);
  HH (b, c, d, a, x[ 2], s34, 0xc4ac5665);

  /* Round 4 */
  II (a, b, c, d, x[ 0], s41, 0xf4292244);
  II (d, a, b, c, x[ 7], s42, 0x432aff97);
  II (c, d, a, b, x[14], s43, 0xab9423a7);
  II (b, c, d, a, x[ 5], s44, 0xfc93a039);
  II (a, b, c, d, x[12], s41, 0x655b59c3);
  II (d, a, b, c, x[ 3], s42, 0x8f0ccc92);
  II (c, d, a, b, x[10], s43, 0xffeff47d);
  II (b, c, d, a, x[ 1], s44, 0x85845dd1);
  II (a, b, c, d, x[ 8], s41, 0x6fa87e4f);
  II (d, a, b, c, x[15], s42, 0xfe2ce6e0);
  II (c, d, a, b, x[ 6], s43, 0xa3014314);
  II (b, c, d, a, x[13], s44, 0x4e0811a1);
  II (a, b, c, d, x[ 4], s41, 0xf7537e82);
  II (d, a, b, c, x[11], s42, 0xbd3af235);
  II (c, d, a, b, x[ 2], s43, 0x2ad7d2bb);
  II (b, c, d, a, x[ 9], s44, 0xeb86d391);

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

/**
* @Encodes input (unsigned long) into output (byte).
*
* @param {input} usigned long.
*
* @param {output} byte.
*
* @param {length} the length of input.
*
*/
void MD5::encode(const bit32* input, byte* output, size_t length) {

  for (size_t i = 0, j = 0; j < length; ++i, j += 4) {
    output[j]= (byte)(input[i] & 0xff);
    output[j + 1] = (byte)((input[i] >> 8) & 0xff);
    output[j + 2] = (byte)((input[i] >> 16) & 0xff);
    output[j + 3] = (byte)((input[i] >> 24) & 0xff);
  }
}

/**
 * @Decodes input (byte) into output (usigned long).
 *
 * @param {input} bytes.
 *
 * @param {output} unsigned long.
 *
 * @param {length} the length of input.
 *
 */
void MD5::decode(const byte* input, bit32* output, size_t length) {
  for (size_t i = 0, j = 0; j < length; ++i, j += 4) {
    output[i] = ((bit32)input[j]) | (((bit32)input[j + 1]) << 8) |
    (((bit32)input[j + 2]) << 16) | (((bit32)input[j + 3]) << 24);
  }
}


/**
 * @Convert digest to string value.
 *
 * @return the hex string of digest.
 *
 */
string MD5::toStr() {
  const byte* digest_ = getDigest();
  string str;
  str.reserve(16 << 1);
  for (size_t i = 0; i < 16; ++i) {
    int t = digest_[i];
    int a = t / 16;
    int b = t % 16;
    str.append(1, HEX_NUMBERS[a]);
    str.append(1, HEX_NUMBERS[b]);
  }
  return str;
}