//
// EQ2-Compatible RC4 Implementation
//
// It differs from standard RC4
// - Fixed 64-bit key (int64_t), treated as 8 bytes in little-endian order
// - Key scheduling cycles through the 8 key bytes using (i & 7)
//

#pragma once

#include <cstdint>
#include <cstddef>
#include <cstring>

class RC4 {
public:
	void init(int64_t key) {
		for (int i = 0; i < 256; ++i)
			S[i] = static_cast<uint8_t>(i);

		uint8_t* keyBytes = reinterpret_cast<uint8_t*>(&key);
		uint8_t j = 0;
		for (int i = 0; i < 256; ++i) {
			j += S[i] + keyBytes[i & 7]; // cycle through 8 key bytes
			std::swap(S[i], S[j]);
		}

		i = 0;
		j = 0;
	}

	void process(uint8_t* data, size_t len) {
		for (size_t n = 0; n < len; ++n) {
			i += 1;
			j += S[i];
			std::swap(S[i], S[j]);
			uint8_t k = S[(S[i] + S[j]) & 0xFF];
			data[n] ^= k;
		}
	}

private:
	uint8_t S[256];
	uint8_t i = 0;
	uint8_t j = 0;
};