// Copyright (c) SHA512 Implementation - MIT License

#pragma once

#include <string>
#include <cstring>
#include <cstdio>

class SHA512
{
protected:
	typedef unsigned char uint8;
	typedef unsigned int uint32;
	typedef unsigned long long uint64;

	// SHA512 round constants (80 64-bit words)
	const static uint64 sha512_k[];
	static const unsigned int SHA384_512_BLOCK_SIZE = (1024/8);

public:
	static const unsigned int DIGEST_SIZE = (512 / 8);

	// Initialize SHA512 context with standard initial hash values
	void init();

	// Process input message data in chunks, handling partial blocks
	void update(const unsigned char *message, unsigned int len);

	// Finalize hash computation and output 64-byte digest
	void final(unsigned char *digest);

protected:
	// Core SHA512 transformation function - processes message blocks
	void transform(const unsigned char *message, unsigned int block_nb);

	unsigned int m_tot_len;	// Total length of processed data
	unsigned int m_len;		// Current length in buffer
	unsigned char m_block[2 * SHA384_512_BLOCK_SIZE];	// Input buffer
	uint64 m_h[8];			// Hash state (8 64-bit words)
};

// Convenience function - compute SHA512 hash of string input
std::string sha512(std::string input);

// SHA2 bit manipulation macros
#define SHA2_SHFR(x, n)    (x >> n)
#define SHA2_ROTR(x, n)   ((x >> n) | (x << ((sizeof(x) << 3) - n)))
#define SHA2_ROTL(x, n)   ((x << n) | (x >> ((sizeof(x) << 3) - n)))
#define SHA2_CH(x, y, z)  ((x & y) ^ (~x & z))
#define SHA2_MAJ(x, y, z) ((x & y) ^ (x & z) ^ (y & z))
#define SHA512_F1(x) (SHA2_ROTR(x, 28) ^ SHA2_ROTR(x, 34) ^ SHA2_ROTR(x, 39))
#define SHA512_F2(x) (SHA2_ROTR(x, 14) ^ SHA2_ROTR(x, 18) ^ SHA2_ROTR(x, 41))
#define SHA512_F3(x) (SHA2_ROTR(x,  1) ^ SHA2_ROTR(x,  8) ^ SHA2_SHFR(x,  7))
#define SHA512_F4(x) (SHA2_ROTR(x, 19) ^ SHA2_ROTR(x, 61) ^ SHA2_SHFR(x,  6))

// Pack/unpack 32-bit and 64-bit values to/from byte arrays (big-endian)
#define SHA2_UNPACK32(x, str)                 \
{                                             \
	*((str) + 3) = (uint8) ((x)      );       \
	*((str) + 2) = (uint8) ((x) >>  8);       \
	*((str) + 1) = (uint8) ((x) >> 16);       \
	*((str) + 0) = (uint8) ((x) >> 24);       \
}

#define SHA2_UNPACK64(x, str)                 \
{                                             \
	*((str) + 7) = (uint8) ((x)      );       \
	*((str) + 6) = (uint8) ((x) >>  8);       \
	*((str) + 5) = (uint8) ((x) >> 16);       \
	*((str) + 4) = (uint8) ((x) >> 24);       \
	*((str) + 3) = (uint8) ((x) >> 32);       \
	*((str) + 2) = (uint8) ((x) >> 40);       \
	*((str) + 1) = (uint8) ((x) >> 48);       \
	*((str) + 0) = (uint8) ((x) >> 56);       \
}

#define SHA2_PACK64(str, x)                   \
{                                             \
	*(x) =   ((uint64) *((str) + 7)      )    \
		   | ((uint64) *((str) + 6) <<  8)    \
		   | ((uint64) *((str) + 5) << 16)    \
		   | ((uint64) *((str) + 4) << 24)    \
		   | ((uint64) *((str) + 3) << 32)    \
		   | ((uint64) *((str) + 2) << 40)    \
		   | ((uint64) *((str) + 1) << 48)    \
		   | ((uint64) *((str) + 0) << 56);   \
}

// SHA512 round constants - precomputed fractional parts of cube roots of first 80 primes
const unsigned long long SHA512::sha512_k[80] = {
	0x428a2f98d728ae22ULL, 0x7137449123ef65cdULL,
	0xb5c0fbcfec4d3b2fULL, 0xe9b5dba58189dbbcULL,
	0x3956c25bf348b538ULL, 0x59f111f1b605d019ULL,
	0x923f82a4af194f9bULL, 0xab1c5ed5da6d8118ULL,
	0xd807aa98a3030242ULL, 0x12835b0145706fbeULL,
	0x243185be4ee4b28cULL, 0x550c7dc3d5ffb4e2ULL,
	0x72be5d74f27b896fULL, 0x80deb1fe3b1696b1ULL,
	0x9bdc06a725c71235ULL, 0xc19bf174cf692694ULL,
	0xe49b69c19ef14ad2ULL, 0xefbe4786384f25e3ULL,
	0x0fc19dc68b8cd5b5ULL, 0x240ca1cc77ac9c65ULL,
	0x2de92c6f592b0275ULL, 0x4a7484aa6ea6e483ULL,
	0x5cb0a9dcbd41fbd4ULL, 0x76f988da831153b5ULL,
	0x983e5152ee66dfabULL, 0xa831c66d2db43210ULL,
	0xb00327c898fb213fULL, 0xbf597fc7beef0ee4ULL,
	0xc6e00bf33da88fc2ULL, 0xd5a79147930aa725ULL,
	0x06ca6351e003826fULL, 0x142929670a0e6e70ULL,
	0x27b70a8546d22ffcULL, 0x2e1b21385c26c926ULL,
	0x4d2c6dfc5ac42aedULL, 0x53380d139d95b3dfULL,
	0x650a73548baf63deULL, 0x766a0abb3c77b2a8ULL,
	0x81c2c92e47edaee6ULL, 0x92722c851482353bULL,
	0xa2bfe8a14cf10364ULL, 0xa81a664bbc423001ULL,
	0xc24b8b70d0f89791ULL, 0xc76c51a30654be30ULL,
	0xd192e819d6ef5218ULL, 0xd69906245565a910ULL,
	0xf40e35855771202aULL, 0x106aa07032bbd1b8ULL,
	0x19a4c116b8d2d0c8ULL, 0x1e376c085141ab53ULL,
	0x2748774cdf8eeb99ULL, 0x34b0bcb5e19b48a8ULL,
	0x391c0cb3c5c95a63ULL, 0x4ed8aa4ae3418acbULL,
	0x5b9cca4f7763e373ULL, 0x682e6ff3d6b2b8a3ULL,
	0x748f82ee5defb2fcULL, 0x78a5636f43172f60ULL,
	0x84c87814a1f0ab72ULL, 0x8cc702081a6439ecULL,
	0x90befffa23631e28ULL, 0xa4506cebde82bde9ULL,
	0xbef9a3f7b2c67915ULL, 0xc67178f2e372532bULL,
	0xca273eceea26619cULL, 0xd186b8c721c0c207ULL,
	0xeada7dd6cde0eb1eULL, 0xf57d4f7fee6ed178ULL,
	0x06f067aa72176fbaULL, 0x0a637dc5a2c898a6ULL,
	0x113f9804bef90daeULL, 0x1b710b35131c471bULL,
	0x28db77f523047d84ULL, 0x32caab7b40c72493ULL,
	0x3c9ebe0a15c9bebcULL, 0x431d67c49c100d4cULL,
	0x4cc5d4becb3e42b6ULL, 0x597f299cfc657e2aULL,
	0x5fcb6fab3ad6faecULL, 0x6c44198c4a475817ULL
};

// Core SHA512 transformation - processes message blocks through compression function
void SHA512::transform(const unsigned char *message, unsigned int block_nb)
{
	uint64 w[80];	// Message schedule array
	uint64 wv[8];	// Working variables
	uint64 t1, t2;	// Temporary values
	const unsigned char *sub_block;
	int i, j;

	// Process each 1024-bit block
	for (i = 0; i < (int) block_nb; i++) {
		sub_block = message + (i << 7);	// Point to current 128-byte block

		// Prepare first 16 words of message schedule from input
		for (j = 0; j < 16; j++) {
			SHA2_PACK64(&sub_block[j << 3], &w[j]);
		}

		// Extend to 80 words using SHA512 message schedule
		for (j = 16; j < 80; j++) {
			w[j] = SHA512_F4(w[j - 2]) + w[j - 7] + SHA512_F3(w[j - 15]) + w[j - 16];
		}

		// Initialize working variables with current hash values
		for (j = 0; j < 8; j++) {
			wv[j] = m_h[j];
		}

		// Main compression loop - 80 rounds
		for (j = 0; j < 80; j++) {
			t1 = wv[7] + SHA512_F2(wv[4]) + SHA2_CH(wv[4], wv[5], wv[6]) + sha512_k[j] + w[j];
			t2 = SHA512_F1(wv[0]) + SHA2_MAJ(wv[0], wv[1], wv[2]);
			wv[7] = wv[6];
			wv[6] = wv[5];
			wv[5] = wv[4];
			wv[4] = wv[3] + t1;
			wv[3] = wv[2];
			wv[2] = wv[1];
			wv[1] = wv[0];
			wv[0] = t1 + t2;
		}

		// Add compressed chunk to current hash values
		for (j = 0; j < 8; j++) {
			m_h[j] += wv[j];
		}
	}
}

// Initialize SHA512 context with standard IV values from FIPS 180-4
void SHA512::init()
{
	m_h[0] = 0x6a09e667f3bcc908ULL;
	m_h[1] = 0xbb67ae8584caa73bULL;
	m_h[2] = 0x3c6ef372fe94f82bULL;
	m_h[3] = 0xa54ff53a5f1d36f1ULL;
	m_h[4] = 0x510e527fade682d1ULL;
	m_h[5] = 0x9b05688c2b3e6c1fULL;
	m_h[6] = 0x1f83d9abfb41bd6bULL;
	m_h[7] = 0x5be0cd19137e2179ULL;
	m_len = 0;
	m_tot_len = 0;
}

// Process input data, handling buffering and block alignment
void SHA512::update(const unsigned char *message, unsigned int len)
{
	unsigned int block_nb;
	unsigned int new_len, rem_len, tmp_len;
	const unsigned char *shifted_message;

	// Calculate space remaining in current block
	tmp_len = SHA384_512_BLOCK_SIZE - m_len;
	rem_len = len < tmp_len ? len : tmp_len;

	// Fill current block buffer
	memcpy(&m_block[m_len], message, rem_len);

	// If block not complete, just update length and return
	if (m_len + len < SHA384_512_BLOCK_SIZE) {
		m_len += len;
		return;
	}

	// Process complete block(s)
	new_len = len - rem_len;
	block_nb = new_len / SHA384_512_BLOCK_SIZE;
	shifted_message = message + rem_len;

	// Transform current buffered block
	transform(m_block, 1);

	// Transform any additional complete blocks
	transform(shifted_message, block_nb);

	// Store remainder in buffer for next update
	rem_len = new_len % SHA384_512_BLOCK_SIZE;
	memcpy(m_block, &shifted_message[block_nb << 7], rem_len);
	m_len = rem_len;
	m_tot_len += (block_nb + 1) << 7;
}

// Finalize hash computation with padding and length encoding
void SHA512::final(unsigned char *digest)
{
	unsigned int block_nb;
	unsigned int pm_len;
	unsigned int len_b;
	int i;

	// Calculate number of blocks needed for padding
	block_nb = 1 + ((SHA384_512_BLOCK_SIZE - 17) < (m_len % SHA384_512_BLOCK_SIZE));

	// Total bit length for final block
	len_b = (m_tot_len + m_len) << 3;
	pm_len = block_nb << 7;

	// Pad with zeros, add required '1' bit, append length
	memset(m_block + m_len, 0, pm_len - m_len);
	m_block[m_len] = 0x80;
	SHA2_UNPACK32(len_b, m_block + pm_len - 4);

	// Process final block(s)
	transform(m_block, block_nb);

	// Output final hash values as big-endian bytes
	for (i = 0; i < 8; i++) {
		SHA2_UNPACK64(m_h[i], &digest[i << 3]);
	}
}

// Convenience function - compute SHA512 hash of string and return as hex
std::string sha512(std::string input)
{
	unsigned char digest[SHA512::DIGEST_SIZE];
	memset(digest, 0, SHA512::DIGEST_SIZE);

	// Initialize context and process input
	SHA512 ctx = SHA512();
	ctx.init();
	ctx.update((unsigned char*)input.c_str(), input.length());
	ctx.final(digest);

	// Convert to hex string
	char buf[2 * SHA512::DIGEST_SIZE + 1];
	buf[2 * SHA512::DIGEST_SIZE] = 0;
	for (int i = 0; i < SHA512::DIGEST_SIZE; i++) {
		sprintf(buf + i * 2, "%02x", digest[i]);
	}
	return std::string(buf);
}