// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (c) 2025 DBZero Software sp. z o.o.

#include "hash.hpp"
#include <cstdint>
#include <cstring>

namespace db0::serial

{

    struct SHA256_CTX
    {
	    std::byte data[64];
	    std::uint32_t datalen = 0;
	    unsigned long long bitlen = 0;
	    std::uint32_t state[8];

        SHA256_CTX()
            : state{0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19}
        {
        }
    };

    #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 const std::uint32_t k[64] = 
    {
        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 sha256_transform(SHA256_CTX &ctx, const std::byte data[])
    {
        std::uint32_t a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];

        for (i = 0, j = 0; i < 16; ++i, j += 4)
            m[i] = (static_cast<std::uint32_t>(data[j]) << 24) | (static_cast<std::uint32_t>(data[j + 1]) << 16) | 
                (static_cast<std::uint32_t>(data[j + 2]) << 8) | (static_cast<std::uint32_t>(data[j + 3]));
        for ( ; i < 64; ++i)
            m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];

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

        for (i = 0; i < 64; ++i) {
            t1 = h + EP1(e) + CH(e,f,g) + k[i] + m[i];
            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;
        }

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

    void sha256_update(SHA256_CTX &ctx, const std::byte data[], std::size_t len)
    {
        std::uint32_t i;
        for (i = 0; i < len; ++i) {
            ctx.data[ctx.datalen] = data[i];
            ++ctx.datalen;
            if (ctx.datalen == 64) {
                sha256_transform(ctx, ctx.data);
                ctx.bitlen += 512;
                ctx.datalen = 0;
            }
        }
    }

    void sha256_final(SHA256_CTX &ctx, std::byte hash[])
    {
        std::uint32_t i;
        i = ctx.datalen;

        // Pad whatever data is left in the buffer.
        if (ctx.datalen < 56) {
            ctx.data[i++] = static_cast<std::byte>(0x80);
            while (i < 56)
                ctx.data[i++] = static_cast<std::byte>(0x00);
        }
        else {
            ctx.data[i++] = static_cast<std::byte>(0x80);
            while (i < 64)
                ctx.data[i++] = static_cast<std::byte>(0x00);
            sha256_transform(ctx, ctx.data);
            std::memset(ctx.data, 0, 56);
        }

        // Append to the padding the total message's length in bits and transform.
        ctx.bitlen += ctx.datalen * 8;
        std::memcpy(&ctx.data[56], &ctx.bitlen, 8);
        sha256_transform(ctx, ctx.data);

        // 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 (i = 0; i < 4; ++i) {
            hash[i]      = static_cast<std::byte>((ctx.state[0] >> (24 - i * 8)) & 0x000000ff);
            hash[i + 4]  = static_cast<std::byte>((ctx.state[1] >> (24 - i * 8)) & 0x000000ff);
            hash[i + 8]  = static_cast<std::byte>((ctx.state[2] >> (24 - i * 8)) & 0x000000ff);
            hash[i + 12] = static_cast<std::byte>((ctx.state[3] >> (24 - i * 8)) & 0x000000ff);
            hash[i + 16] = static_cast<std::byte>((ctx.state[4] >> (24 - i * 8)) & 0x000000ff);
            hash[i + 20] = static_cast<std::byte>((ctx.state[5] >> (24 - i * 8)) & 0x000000ff);
            hash[i + 24] = static_cast<std::byte>((ctx.state[6] >> (24 - i * 8)) & 0x000000ff);
            hash[i + 28] = static_cast<std::byte>((ctx.state[7] >> (24 - i * 8)) & 0x000000ff);
        }
    }
    
    void sha256(const std::uint8_t* message, std::uint64_t len, std::byte hash[32])
    {
        SHA256_CTX ctx;
        sha256_update(ctx, reinterpret_cast<const std::byte *>(message), len);
        sha256_final(ctx, hash);
    }

    void sha256(const std::vector<std::byte> &message, std::vector<std::byte> &output) 
    {
        auto index = output.size();
        output.resize(index + 32);
        sha256(reinterpret_cast<const std::uint8_t *>(message.data()), message.size(), output.data() + index);
    }
    
}
