// Copyright (C) 2007 EQ2EMulator Development Team, GPL v3

#pragma once

#include <cstring>
#include <cstdint>
#include <cstdio>
#include <cctype>

class MD5
{
public:
	// MD5 computation context structure
	struct MD5Context
	{
		std::uint32_t hash[4];		// Current hash state
		std::uint32_t bytes[2];		// Number of bytes processed (64-bit counter)
		std::uint32_t input[16];	// Input buffer for 64-byte blocks
	};

	// Static method to generate MD5 hash from buffer
	static void Generate(const std::int8_t* buf, std::uint32_t len, std::int8_t digest[16]);
	
	// Initialize MD5 context for incremental hashing
	static void Init(struct MD5Context *context);
	
	// Update MD5 context with additional data
	static void Update(struct MD5Context *context, const std::int8_t *buf, std::uint32_t len);
	
	// Finalize MD5 computation and produce digest
	static void Final(std::int8_t digest[16], struct MD5Context *context);

	// Default constructor - initializes to zero hash
	MD5();
	
	// Constructor from unsigned char buffer
	MD5(const unsigned char* buf, std::uint32_t len);
	
	// Constructor from char buffer
	MD5(const char* buf, std::uint32_t len);
	
	// Constructor from 16-byte binary hash
	MD5(const std::int8_t buf[16]);
	
	// Constructor from hex string representation
	MD5(const char* iMD5String);
	
	// Generate MD5 from null-terminated string
	void Generate(const char* iString);
	
	// Generate MD5 from buffer
	void Generate(const std::int8_t* buf, std::uint32_t len);
	
	// Set MD5 from 16-byte binary data
	bool Set(const std::int8_t buf[16]);
	
	// Set MD5 from 32-character hex string
	bool Set(const char* iMD5String);

	// Equality comparison operators
	bool operator== (const MD5& iMD5);
	bool operator== (const std::int8_t iMD5[16]);
	bool operator== (const char* iMD5String);

	// Assignment operators
	MD5& operator= (const MD5& iMD5);
	MD5* operator= (const MD5* iMD5);
	
	// Conversion to hex string
	operator const char* ();

private:
	// Helper function to convert bytes to little-endian format
	static void byteSwap(std::uint32_t *buf, std::uint32_t words);
	
	// Core MD5 transformation function
	static void Transform(std::uint32_t hash[4], const std::uint32_t input[16]);
	
	// Helper function to check if character is valid hex digit
	static bool IsHexDigit(char c) {
		return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');
	}
	
	// Helper function to convert hex string to integer
	static std::uint32_t HexToInt(const char* hex) {
		std::uint32_t result = 0;
		for (int i = 0; hex[i] != '\0'; ++i) {
			result *= 16;
			if (hex[i] >= '0' && hex[i] <= '9') {
				result += hex[i] - '0';
			} else if (hex[i] >= 'a' && hex[i] <= 'f') {
				result += hex[i] - 'a' + 10;
			} else if (hex[i] >= 'A' && hex[i] <= 'F') {
				result += hex[i] - 'A' + 10;
			}
		}
		return result;
	}

	std::int8_t pMD5[16];		// 16-byte MD5 hash storage
	char pMD5String[33];		// 32-character hex string representation + null terminator
};

// Default constructor - zero out hash
MD5::MD5() {
	std::memset(pMD5, 0, 16);
}

// Constructor from unsigned char buffer
MD5::MD5(const unsigned char* buf, std::uint32_t len) {
	Generate(reinterpret_cast<const std::int8_t*>(buf), len, pMD5);
}

// Constructor from char buffer
MD5::MD5(const char* buf, std::uint32_t len) {
	Generate(reinterpret_cast<const std::int8_t*>(buf), len, pMD5);
}

// Constructor from 16-byte binary hash
MD5::MD5(const std::int8_t buf[16]) {
	Set(buf);
}

// Constructor from hex string
MD5::MD5(const char* iMD5String) {
	Set(iMD5String);
}

// Generate MD5 from null-terminated string
void MD5::Generate(const char* iString) {
	Generate(reinterpret_cast<const std::int8_t*>(iString), std::strlen(iString));
}

// Generate MD5 from buffer using instance method
void MD5::Generate(const std::int8_t* buf, std::uint32_t len) {
	Generate(buf, len, pMD5);
}

// Set MD5 from 16-byte binary data
bool MD5::Set(const std::int8_t buf[16]) {
	std::memcpy(pMD5, buf, 16);
	return true;
}

// Set MD5 from 32-character hex string
bool MD5::Set(const char* iMD5String) {
	char tmp[5] = { '0', 'x', 0, 0, 0 };
	for (int i = 0; i < 16; i++) {
		tmp[2] = iMD5String[i * 2];
		tmp[3] = iMD5String[(i * 2) + 1];
		
		// Validate hex characters
		if (!IsHexDigit(tmp[2]) || !IsHexDigit(tmp[3]))
			return false;
			
		pMD5[i] = static_cast<std::int8_t>(HexToInt(tmp));
	}
	return true;
}

// Convert MD5 to hex string representation
MD5::operator const char* () {
	std::snprintf(pMD5String, sizeof(pMD5String), 
		"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
		static_cast<unsigned char>(pMD5[0]), static_cast<unsigned char>(pMD5[1]), 
		static_cast<unsigned char>(pMD5[2]), static_cast<unsigned char>(pMD5[3]),
		static_cast<unsigned char>(pMD5[4]), static_cast<unsigned char>(pMD5[5]),
		static_cast<unsigned char>(pMD5[6]), static_cast<unsigned char>(pMD5[7]),
		static_cast<unsigned char>(pMD5[8]), static_cast<unsigned char>(pMD5[9]),
		static_cast<unsigned char>(pMD5[10]), static_cast<unsigned char>(pMD5[11]),
		static_cast<unsigned char>(pMD5[12]), static_cast<unsigned char>(pMD5[13]),
		static_cast<unsigned char>(pMD5[14]), static_cast<unsigned char>(pMD5[15]));
	return pMD5String;
}

// Equality comparison with another MD5 object
bool MD5::operator== (const MD5& iMD5) {
	return std::memcmp(pMD5, iMD5.pMD5, 16) == 0;
}

// Equality comparison with 16-byte array
bool MD5::operator== (const std::int8_t* iMD5) {
	return std::memcmp(pMD5, iMD5, 16) == 0;
}

// Equality comparison with hex string
bool MD5::operator== (const char* iMD5String) {
	char tmp[5] = { '0', 'x', 0, 0, 0 };
	for (int i = 0; i < 16; i++) {
		tmp[2] = iMD5String[i * 2];
		tmp[3] = iMD5String[(i * 2) + 1];
		if (pMD5[i] != static_cast<std::int8_t>(HexToInt(tmp)))
			return false;
	}
	return true;
}

// Assignment from another MD5 object
MD5& MD5::operator= (const MD5& iMD5) {
	std::memcpy(pMD5, iMD5.pMD5, 16);
	return *this;
}

// Assignment from MD5 pointer
MD5* MD5::operator= (const MD5* iMD5) {
	std::memcpy(pMD5, iMD5->pMD5, 16);
	return this;
}

// Byte-swap array of 32-bit words to little-endian format
void MD5::byteSwap(std::uint32_t *buf, std::uint32_t words) {
	std::int8_t *p = reinterpret_cast<std::int8_t*>(buf);
	do {
		*buf++ = (static_cast<std::uint32_t>(static_cast<std::uint32_t>(p[3]) << 8 | p[2]) << 16) |
				(static_cast<std::uint32_t>(p[1]) << 8 | p[0]);
		p += 4;
	} while (--words);
}

// Generate MD5 digest from buffer using static method
void MD5::Generate(const std::int8_t* buf, std::uint32_t len, std::int8_t digest[16]) {
	MD5Context ctx;
	Init(&ctx);
	Update(&ctx, buf, len);
	Final(digest, &ctx);
}

// Initialize MD5 context with standard initial values
void MD5::Init(struct MD5Context *ctx) {
	ctx->hash[0] = 0x67452301;
	ctx->hash[1] = 0xefcdab89;
	ctx->hash[2] = 0x98badcfe;
	ctx->hash[3] = 0x10325476;
	ctx->bytes[1] = ctx->bytes[0] = 0;
}

// Update MD5 context with new data
void MD5::Update(struct MD5Context *ctx, std::int8_t const *buf, std::uint32_t len) {
	std::uint32_t t = ctx->bytes[0];
	if ((ctx->bytes[0] = t + len) < t)  // Update 64-bit byte count
		ctx->bytes[1]++;    // Carry from low to high

	t = 64 - (t & 0x3f);    // Bytes available in ctx->input (>= 1)
	if (t > len) {
		std::memcpy(reinterpret_cast<std::int8_t*>(ctx->input) + 64 - t, buf, len);
		return;
	}
	
	// First chunk is an odd size
	std::memcpy(reinterpret_cast<std::int8_t*>(ctx->input) + 64 - t, buf, t);
	byteSwap(ctx->input, 16);
	Transform(ctx->hash, ctx->input);
	buf += t;
	len -= t;
	
	// Process data in 64-byte chunks
	while (len >= 64) {
		std::memcpy(ctx->input, buf, 64);
		byteSwap(ctx->input, 16);
		Transform(ctx->hash, ctx->input);
		buf += 64;
		len -= 64;
	}
	
	// Buffer any remaining bytes of data
	std::memcpy(ctx->input, buf, len);
}

// Finalize MD5 computation with padding and length
void MD5::Final(std::int8_t digest[16], MD5Context *ctx) {
	int count = ctx->bytes[0] & 0x3F;   // Bytes mod 64
	std::int8_t *p = reinterpret_cast<std::int8_t*>(ctx->input) + count;
	
	// Set the first byte of padding to 0x80. There is always room.
	*p++ = 0x80;
	
	// Bytes of zero padding needed to make 56 bytes (-8..55)
	count = 56 - 1 - count;
	if (count < 0) {    // Padding forces an extra block
		std::memset(p, 0, count + 8);
		byteSwap(ctx->input, 16);
		Transform(ctx->hash, ctx->input);
		p = reinterpret_cast<std::int8_t*>(ctx->input);
		count = 56;
	}
	std::memset(p, 0, count);
	byteSwap(ctx->input, 14);
	
	// Append 8 bytes of length in *bits* and transform
	ctx->input[14] = ctx->bytes[0] << 3;
	ctx->input[15] = ctx->bytes[1] << 3 | ctx->bytes[0] >> 29;
	Transform(ctx->hash, ctx->input);
	byteSwap(ctx->hash, 4);
	std::memcpy(digest, ctx->hash, 16);
	std::memset(ctx, 0, sizeof(*ctx));   // Clear sensitive data
}

// MD5 transformation constants and helper functions
#define F1(x, y, z) (z ^ (x & (y ^ z)))
#define F2(x, y, z) F1(z, x, y)
#define F3(x, y, z) (x ^ y ^ z)
#define F4(x, y, z) (y ^ (x | ~z))

// Central step in MD5 algorithm
#define MD5STEP(f,w,x,y,z,in,s) (w += f(x,y,z)+in, w = (w<<s | w>>(32-s)) + x)

// Core MD5 transformation function - processes one 64-byte block
void MD5::Transform(std::uint32_t hash[4], const std::uint32_t input[16]) {
	std::uint32_t a = hash[0], b = hash[1], c = hash[2], d = hash[3];

	// Round 1 - F1 function
	MD5STEP(F1, a, b, c, d, input[ 0]+0xd76aa478,  7);
	MD5STEP(F1, d, a, b, c, input[ 1]+0xe8c7b756, 12);
	MD5STEP(F1, c, d, a, b, input[ 2]+0x242070db, 17);
	MD5STEP(F1, b, c, d, a, input[ 3]+0xc1bdceee, 22);
	MD5STEP(F1, a, b, c, d, input[ 4]+0xf57c0faf,  7);
	MD5STEP(F1, d, a, b, c, input[ 5]+0x4787c62a, 12);
	MD5STEP(F1, c, d, a, b, input[ 6]+0xa8304613, 17);
	MD5STEP(F1, b, c, d, a, input[ 7]+0xfd469501, 22);
	MD5STEP(F1, a, b, c, d, input[ 8]+0x698098d8,  7);
	MD5STEP(F1, d, a, b, c, input[ 9]+0x8b44f7af, 12);
	MD5STEP(F1, c, d, a, b, input[10]+0xffff5bb1, 17);
	MD5STEP(F1, b, c, d, a, input[11]+0x895cd7be, 22);
	MD5STEP(F1, a, b, c, d, input[12]+0x6b901122,  7);
	MD5STEP(F1, d, a, b, c, input[13]+0xfd987193, 12);
	MD5STEP(F1, c, d, a, b, input[14]+0xa679438e, 17);
	MD5STEP(F1, b, c, d, a, input[15]+0x49b40821, 22);

	// Round 2 - F2 function
	MD5STEP(F2, a, b, c, d, input[ 1]+0xf61e2562,  5);
	MD5STEP(F2, d, a, b, c, input[ 6]+0xc040b340,  9);
	MD5STEP(F2, c, d, a, b, input[11]+0x265e5a51, 14);
	MD5STEP(F2, b, c, d, a, input[ 0]+0xe9b6c7aa, 20);
	MD5STEP(F2, a, b, c, d, input[ 5]+0xd62f105d,  5);
	MD5STEP(F2, d, a, b, c, input[10]+0x02441453,  9);
	MD5STEP(F2, c, d, a, b, input[15]+0xd8a1e681, 14);
	MD5STEP(F2, b, c, d, a, input[ 4]+0xe7d3fbc8, 20);
	MD5STEP(F2, a, b, c, d, input[ 9]+0x21e1cde6,  5);
	MD5STEP(F2, d, a, b, c, input[14]+0xc33707d6,  9);
	MD5STEP(F2, c, d, a, b, input[ 3]+0xf4d50d87, 14);
	MD5STEP(F2, b, c, d, a, input[ 8]+0x455a14ed, 20);
	MD5STEP(F2, a, b, c, d, input[13]+0xa9e3e905,  5);
	MD5STEP(F2, d, a, b, c, input[ 2]+0xfcefa3f8,  9);
	MD5STEP(F2, c, d, a, b, input[ 7]+0x676f02d9, 14);
	MD5STEP(F2, b, c, d, a, input[12]+0x8d2a4c8a, 20);

	// Round 3 - F3 function
	MD5STEP(F3, a, b, c, d, input[ 5]+0xfffa3942,  4);
	MD5STEP(F3, d, a, b, c, input[ 8]+0x8771f681, 11);
	MD5STEP(F3, c, d, a, b, input[11]+0x6d9d6122, 16);
	MD5STEP(F3, b, c, d, a, input[14]+0xfde5380c, 23);
	MD5STEP(F3, a, b, c, d, input[ 1]+0xa4beea44,  4);
	MD5STEP(F3, d, a, b, c, input[ 4]+0x4bdecfa9, 11);
	MD5STEP(F3, c, d, a, b, input[ 7]+0xf6bb4b60, 16);
	MD5STEP(F3, b, c, d, a, input[10]+0xbebfbc70, 23);
	MD5STEP(F3, a, b, c, d, input[13]+0x289b7ec6,  4);
	MD5STEP(F3, d, a, b, c, input[ 0]+0xeaa127fa, 11);
	MD5STEP(F3, c, d, a, b, input[ 3]+0xd4ef3085, 16);
	MD5STEP(F3, b, c, d, a, input[ 6]+0x04881d05, 23);
	MD5STEP(F3, a, b, c, d, input[ 9]+0xd9d4d039,  4);
	MD5STEP(F3, d, a, b, c, input[12]+0xe6db99e5, 11);
	MD5STEP(F3, c, d, a, b, input[15]+0x1fa27cf8, 16);
	MD5STEP(F3, b, c, d, a, input[ 2]+0xc4ac5665, 23);

	// Round 4 - F4 function
	MD5STEP(F4, a, b, c, d, input[ 0]+0xf4292244,  6);
	MD5STEP(F4, d, a, b, c, input[ 7]+0x432aff97, 10);
	MD5STEP(F4, c, d, a, b, input[14]+0xab9423a7, 15);
	MD5STEP(F4, b, c, d, a, input[ 5]+0xfc93a039, 21);
	MD5STEP(F4, a, b, c, d, input[12]+0x655b59c3,  6);
	MD5STEP(F4, d, a, b, c, input[ 3]+0x8f0ccc92, 10);
	MD5STEP(F4, c, d, a, b, input[10]+0xffeff47d, 15);
	MD5STEP(F4, b, c, d, a, input[ 1]+0x85845dd1, 21);
	MD5STEP(F4, a, b, c, d, input[ 8]+0x6fa87e4f,  6);
	MD5STEP(F4, d, a, b, c, input[15]+0xfe2ce6e0, 10);
	MD5STEP(F4, c, d, a, b, input[ 6]+0xa3014314, 15);
	MD5STEP(F4, b, c, d, a, input[13]+0x4e0811a1, 21);
	MD5STEP(F4, a, b, c, d, input[ 4]+0xf7537e82,  6);
	MD5STEP(F4, d, a, b, c, input[11]+0xbd3af235, 10);
	MD5STEP(F4, c, d, a, b, input[ 2]+0x2ad7d2bb, 15);
	MD5STEP(F4, b, c, d, a, input[ 9]+0xeb86d391, 21);

	// Add the working variables back into the hash state
	hash[0] += a;
	hash[1] += b;
	hash[2] += c;
	hash[3] += d;
}