/*
* Filename: sha256.cpp
* Author: L.Y.
* Brief: SHA256算法实现
* Version: V1.0.0
* Update log:
*     1）20191108-20191113 V1.0.0
*         1、初次版本。
* TODO:
* Attention:
*     1）输入信息中有中文时，得到的数字指纹与使用SHA256在线加密工具得到数字指纹可能不相同。
*        原因是中文的编码方式不同。
*/

#include "sha256.hpp"

#include <iomanip>
#include <sstream>
#include <string>
#include <vector>

namespace digest
{

//////////////////////////////// 静态数据成员初始化 //////////////////////////////////////////

    std::vector<uint32_t> Sha256::initial_message_digest_ =
            {
                    0x6a09e667, 0xbb67ae85, 0x3c6ef372,
                    0xa54ff53a, 0x510e527f, 0x9b05688c,
                    0x1f83d9ab, 0x5be0cd19
            };

    std::vector<uint32_t> Sha256::add_constant_ =
            {
                    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
            };


//////////////////////////////// 成员函数的定义 //////////////////////////////////////////

    bool Sha256::encrypt(const std::vector<uint8_t>& input_message,
                         std::vector<uint8_t>* _digest)
    {
        if (!input_message.empty() && _digest)
        {
            //! 文本预处理
            std::vector<uint8_t> message = input_message;
            preprocessing(&message);

            //! 将文本分解成连续的64Byte大小的数据块
            std::vector<std::vector<uint8_t>> chunks;
            breakTextInto64ByteChunks(message, &chunks);

            //! 由64Byte大小的数据块，构造出64个4Byte大小的字。然后进行循环迭代。
            std::vector<uint32_t> message_digest(initial_message_digest_); // 初始化信息摘要

            std::vector<uint32_t> words;
            for (const auto& chunk : chunks)
            {
                structureWords(chunk, &words);
                transform(words, &message_digest);
            }

            //! 获取最终结果
            produceFinalHashValue(message_digest, _digest);

            return true;
        }
        else
        {
            return false;
        }
    }

    std::string Sha256::getHexMessageDigest(const std::string& message)
    {
        if (!message.empty())
        {
            std::vector<uint8_t> __message;
            for (auto it = message.begin(); it != message.end(); ++it)
            {
                __message.push_back(static_cast<uint8_t>(*it));
            }

            std::vector<uint8_t> digest;
            encrypt(__message, &digest);

            std::ostringstream o_s;
            o_s << std::hex << std::setiosflags(std::ios::uppercase);
            for (auto it = digest.begin(); it != digest.end(); ++it)
            {
                o_s << std::setw(2) << std::setfill('0')
                    << static_cast<unsigned short>(*it);
            }

            return o_s.str();
        }
        else
        {
            return "";
        }
    }

    bool Sha256::preprocessing(std::vector<uint8_t>* _message) const
    {
        if (_message)
        {
            const uint64_t original_bit_size = _message->size() * 8;

            //! 附加填充比特
            size_t remainder = _message->size() % 64;
            if (remainder < 56)
            {
                _message->push_back(0x80); // ox80 == 10000000
                for (size_t i = 1; i < 56 - remainder; ++i)
                {
                    _message->push_back(0x00);
                }
            }
            else if (remainder == 56)
            {
                _message->push_back(0x80);
                for (size_t i = 1; i < 64; ++i)
                {
                    _message->push_back(0x00);
                }
            }
            else
            {
                _message->push_back(0x80);
                for (size_t i = 1; i < 64 - remainder + 56; ++i)
                {
                    _message->push_back(0x00);
                }
            }

            //! 附加原始文本的长度值
            for (int i = 1; i <= 8; ++i)
            {
                uint8_t c = static_cast<uint8_t>(original_bit_size >> (64 - 8 * i));
                _message->push_back(c);
            }

            return true;
        }
        else
        {
            return false;
        }
    }

    bool Sha256::breakTextInto64ByteChunks(const std::vector<uint8_t>& message,
                                           std::vector<std::vector<uint8_t>>* _chunks) const
    {
        if (_chunks && 0 == message.size() % 64)
        {
            _chunks->clear(); // 清空输出buffer

            size_t quotient = message.size() / 64;
            for (size_t i = 0; i < quotient; ++i)
            {
                std::vector<uint8_t> temp(message.begin() + i * 64, message.begin() + (i + 1) * 64);
                _chunks->push_back(temp);
            }
            return true;
        }
        else
        {
            return false;
        }
    }

    bool Sha256::structureWords(const std::vector<uint8_t>& chunk,
                                std::vector<uint32_t>* _words) const
    {
        if (_words && 64 == chunk.size())
        {
            _words->resize(64);

            auto& words = *_words;
            for (int i = 0; i < 16; ++i)
            {
                words[i] = (static_cast<uint32_t>(chunk[i * 4]) << 24)
                           | (static_cast<uint32_t>(chunk[i * 4 + 1]) << 16)
                           | (static_cast<uint32_t>(chunk[i * 4 + 2]) << 8)
                           | static_cast<uint32_t>(chunk[i * 4 + 3]);
            }
            for (int i = 16; i < 64; ++i)
            {
                words[i] = small_sigma1(words[i - 2])
                           + words[i - 7]
                           + small_sigma0(words[i - 15])
                           + words[i - 16];
            }
            return true;
        }
        else
        {
            return false;
        }
    }

    bool Sha256::transform(const std::vector<uint32_t>& words,
                           std::vector<uint32_t>* _message_digest) const
    {
        if (_message_digest && 8 == _message_digest->size() && 64 == words.size())
        {
            std::vector<uint32_t> d = *_message_digest;

            for (int i = 0; i < 64; ++i)
            {
                uint32_t temp1 = d[7] + big_sigma1(d[4]) + ch(d[4], d[5], d[6]) + add_constant_[i] + words[i];
                uint32_t temp2 = big_sigma0(d[0]) + maj(d[0], d[1], d[2]);

                d[7] = d[6];
                d[6] = d[5];
                d[5] = d[4];
                d[4] = d[3] + temp1;
                d[3] = d[2];
                d[2] = d[1];
                d[1] = d[0];
                d[0] = temp1 + temp2;
            }

            for (int i = 0; i < 8; ++i)
            {
                (*_message_digest)[i] += d[i];
            }

            return true;
        }
        else
        {
            return false;
        }
    }

    bool Sha256::produceFinalHashValue(const std::vector<uint32_t>& input,
                                       std::vector<uint8_t>* _output) const
    {
        if (_output)
        {
            _output->clear();

            for (auto it = input.begin(); it != input.end(); ++it)
            {
                for (int i = 0; i < 4; i++)
                {
                    _output->push_back(static_cast<uint8_t>((*it) >> (24 - 8 * i)));
                }
            }
            return true;
        }
        else
        {
            return false;
        }
    }

} // namespace ly