#pragma once

#include <cstdint>
#include <cstddef>
#include <algorithm>

class RC4 {
public:
	void init(const uint8_t* key, size_t keyLen) {
		for (int k = 0; k < 256; ++k)
			S[k] = static_cast<uint8_t>(k);

		uint8_t j = 0;
		for (int k = 0; k < 256; ++k) {
			j += S[k] + key[k % keyLen];
			std::swap(S[k], 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;
};