// This file is part of a crypto library, exam for the Algorithms class.
// All of these files are under MIT license.
//
// SHA declaration document:
// https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf

#ifndef HMACSHA256_SHA256_H_
#define HMACSHA256_SHA256_H_

#include "sha.h"
#include <array>
#include <cstdint>

namespace hmacsha256 {
class SHA256 : public SHA {
public:
    // create a new SHA256 thanks an array of bytes
    SHA256(const uint8_t*, uint32_t);

    SHA256(const std::string&);

    // get digest as array of bytes
    uint8_t* digest() override;

    std::string hexdigest() override;

private:
    // first 80 costansts 64bit words, paragraph 4.2.2
    std::array<uint32_t, 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
    };

    // the constructor
    void init(const uint8_t* data, uint32_t length) override;

    // Ch(x, y, z) = (x | y) ^ (~x & z)
    static uint32_t ch(uint32_t, uint32_t, uint32_t);

    // Maj(x, y, z) = (x | y) ^ (x & z) ^ (y & z)
    static uint32_t maj(uint32_t, uint32_t, uint32_t);

    // circular right shift. Takes two params: `x` a w-bit word and `n` an int
    // with 0 <= n < w.
    // w, in our case is 32
    //
    // rots is also defined in the NIST document as
    // rotr(x) = (x >> n) or (x << w - n)
    static uint32_t rotr(uint32_t, uint32_t);

    // function defined in 4.4
    static uint32_t big_sigma0(uint32_t);

    // function defined in 4.5
    static uint32_t big_sigma1(uint32_t);

    // function defined in 4.6
    static uint32_t sigma0(uint32_t);

    // function defined in 4.7
    static uint32_t sigma1(uint32_t);

    // padding
    void pad() override;

    // main function
    void transform() override;

    // transform bytes in big-endian, because SHA256 wants big endian ordering
    // Takes 1 parameter, the array of bytes that we want to reorder
    void bigendian(uint8_t*);
};

} // namespace hmacsha256

#endif // HMACSHA256_SHA256_H_