/**
 *
 */

// SHA256 implementation from
// https://github.com/B-Con/crypto-algorithms/tree/master

/*********************************************************************
* Filename:   sha256.c
* Author:     Brad Conte (brad AT bradconte.com)
* Copyright:
* Disclaimer: This code is presented "as is" without any guarantees.
* Details:    Implementation of the SHA-256 hashing algorithm.
              SHA-256 is one of the three algorithms in the SHA2
              specification. The others, SHA-384 and SHA-512, are not
              offered in this implementation.
              Algorithm specification can be found here:
               * http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf
              This implementation uses little endian byte order.
*********************************************************************/

/*************************** HEADER FILES ***************************/
#include "ee382n_bitcoin/sha256.h"

#include <assert.h>
#include <memory.h>
#include <stdlib.h>
#include <stdio.h>
#include <arpa/inet.h>


/****************************** MACROS ******************************/
#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))

/**************************** VARIABLES *****************************/
static const WORD 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};

/*********************** FUNCTION DEFINITIONS ***********************/
void sha256_transform(SHA256_CTX *ctx, const BYTE data[]) {
    WORD 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] = (data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) |
               (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_init(SHA256_CTX *ctx) {
    ctx->datalen = 0;
    ctx->bitlen = 0;
    ctx->state[0] = 0x6a09e667;
    ctx->state[1] = 0xbb67ae85;
    ctx->state[2] = 0x3c6ef372;
    ctx->state[3] = 0xa54ff53a;
    ctx->state[4] = 0x510e527f;
    ctx->state[5] = 0x9b05688c;
    ctx->state[6] = 0x1f83d9ab;
    ctx->state[7] = 0x5be0cd19;
}

void sha256_update(SHA256_CTX *ctx, const BYTE data[], size_t len) {
    WORD 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, BYTE hash[]) {
    WORD i;

    i = ctx->datalen;

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

    // Append to the padding the total message's length in bits and transform.
    ctx->bitlen += ctx->datalen * 8;
    ctx->data[63] = ctx->bitlen;
    ctx->data[62] = ctx->bitlen >> 8;
    ctx->data[61] = ctx->bitlen >> 16;
    ctx->data[60] = ctx->bitlen >> 24;
    ctx->data[59] = ctx->bitlen >> 32;
    ctx->data[58] = ctx->bitlen >> 40;
    ctx->data[57] = ctx->bitlen >> 48;
    ctx->data[56] = ctx->bitlen >> 56;
    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] = (ctx->state[0] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 4] = (ctx->state[1] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 8] = (ctx->state[2] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 12] = (ctx->state[3] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 16] = (ctx->state[4] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0x000000ff;
    }
}

/**
 * @brief Double SHA-256 hash function
 *
 * @param data input data
 * @param len data length in bytes
 * @param hash 256 bit output array for resulting hash
 */
void sha256_double(const BYTE data[], size_t len, BYTE hash[]) {
    SHA256_CTX ctx;
    // First SHA256 hash
    sha256_init(&ctx);
    sha256_update(&ctx, data, len);
    sha256_final(&ctx, hash);
    // Second SHA256 hash
    sha256_init(&ctx);
    sha256_update(&ctx, hash, SHA256_BLOCK_SIZE);
    sha256_final(&ctx, hash);
    // Now hash = SHA256(SHA256(data))
}


/**
 * @brief Implementation of SHA-256 algorithm derived from Wikipedia SHA-256 pseudocode
 *
 * @param data
 * @param len Length of data in bytes
 * @param hash Pointer to 256 byte hash output
 */
void sha256_wiki_single(const BYTE data[], size_t len, BYTE hash[]) {
    WORD h0, h1, h2, h3, h4, h5, h6, h7;
    WORD w[64];

    // Initialize hash values
    h0 = 0x6a09e667;
    h1 = 0xbb67ae85;
    h2 = 0x3c6ef372;
    h3 = 0xa54ff53a;
    h4 = 0x510e527f;
    h5 = 0x9b05688c;
    h6 = 0x1f83d9ab;
    h7 = 0x5be0cd19;

    // Pre-processing (padding) - Combine with the next step
    // Leave room for appending 1 (0x80) and 64-bit message length
    size_t min_len = len + 1 + 8;
    size_t padding_bytes = 64 - (min_len % 64);
    size_t modified_len = min_len + padding_bytes;
    // Message size after padding must be multiple of 512 bits (64 bytes)
    assert(modified_len % 64 == 0);

    // Process message in successive 512-bit (64 byte) chunks:
    for(int chunk = 0; chunk < modified_len; chunk += 64) {
        // Copy chunk into first 16 words (64 bytes) w[0..15]
        for(int i = 0; i < 64; i++) {
            if((chunk + i) < len) {
                ((BYTE *)w)[i] = data[chunk + i];
            } else if(chunk + i == len) {
                ((BYTE *)w)[i] = 0x80;
            } else {
                ((BYTE *)w)[i] = 0x00;
            }
        }

        // Last chunk gets 64-bit big endian length in bits appended to end
        if(chunk + 64 >= modified_len) {
            size_t bitlen = len * 8;
            ((BYTE *)w)[63] = bitlen;
            ((BYTE *)w)[62] = bitlen >> 8;
            ((BYTE *)w)[61] = bitlen >> 16;
            ((BYTE *)w)[60] = bitlen >> 24;
            ((BYTE *)w)[59] = bitlen >> 32;
            ((BYTE *)w)[58] = bitlen >> 40;
            ((BYTE *)w)[57] = bitlen >> 48;
            ((BYTE *)w)[56] = bitlen >> 56;
        }

        // DEBUG: Print chunked input
        // printf("Chunk %d:\t\t0x", chunk);
        // for(int i = 0; i < 16; i++) {
        //   printf("%08X", htonl(w[i]));
        // }
        // printf("\n");

        // Swap endianness of 16 input words
        for(int i = 0; i < 64; i++) {
            w[i] = htonl(w[i]);
        }

        // Extend the first 16 words into the remaining 48 words
        for(int i = 16; i < 64; i++) {
            WORD s0 = ROTRIGHT(w[i - 15], 7) ^ ROTRIGHT(w[i-15], 18) ^ (w[i-15] >> 3);
            WORD s1 = ROTRIGHT(w[i-2], 17) ^ ROTRIGHT(w[i-2], 19) ^ (w[i-2] >> 10);
            w[i] = w[i-16] + s0 + w[i-7] + s1;
        }

        // Initialize working variables to current hash value
        WORD a, b, c, d, e, f, g, h;
        a = h0;
        b = h1;
        c = h2;
        d = h3;
        e = h4;
        f = h5;
        g = h6;
        h = h7;

        // Compression function main loop
        for(int i = 0; i < 64; i++) {
            WORD S0, S1, ch, temp1, temp2, maj;
            S1 = ROTRIGHT(e, 6) ^ ROTRIGHT(e, 11) ^ ROTRIGHT(e, 25);
            ch = (e & f) ^ (~e & g);
            temp1 = h + S1 + ch + k[i] + w[i];
            S0 = ROTRIGHT(a, 2) ^ ROTRIGHT(a, 13) ^ ROTRIGHT(a, 22);
            maj = (a & b) ^ (a & c) ^ (b & c);
            temp2 = S0 + maj;

            h = g;
            g = f;
            f = e;
            e = d + temp1;
            d = c;
            c = b;
            b = a;
            a = temp1 + temp2;
        }

        // Add the compressed chunk to the current hash value
        h0 += a;
        h1 += b;
        h2 += c;
        h3 += d;
        h4 += e;
        h5 += f;
        h6 += g;
        h7 += h;
    }

    // printf("Hash: %08X %08X %08X %08X %08X %08X %08X %08X\n", h0, h1, h2, h3, h4, h5, h6, h7);
    ((WORD *)hash)[0] = htonl(h0);
    ((WORD *)hash)[1] = htonl(h1);
    ((WORD *)hash)[2] = htonl(h2);
    ((WORD *)hash)[3] = htonl(h3);
    ((WORD *)hash)[4] = htonl(h4);
    ((WORD *)hash)[5] = htonl(h5);
    ((WORD *)hash)[6] = htonl(h6);
    ((WORD *)hash)[7] = htonl(h7);
}

/**
 * @brief Double SHA-256 using sha256_wiki_single implementation
 *
 * @param data
 * @param len Length of data in bytes
 * @param hash Pointer to 256 byte hash output
 */
void sha256_wiki_double(const BYTE data[], size_t len, BYTE hash[]) {
    sha256_wiki_single(data, len, hash);
    // DEBUG: Print intermediate hash
    // printf("sha256_wiki_double intermediate hash:\n0x");
    // for (int i = SHA256_BLOCK_SIZE; i > 0; i--) {
    //   printf("%02X", hash[i-1]);
    // }
    // printf("\n");

    sha256_wiki_single(hash, SHA256_BLOCK_SIZE, hash);
    // DEBUG: Print final hash
    // printf("sha256_wiki_double final hash:\n0x");
    // for (int i = SHA256_BLOCK_SIZE; i > 0; i--) {
    //   printf("%02X", hash[i-1]);
    // }
    // printf("\n");
}