// Copyright (C) 2007-2025 EQ2EMulator
// Licensed under GPL v3

#include "rc4.h"
#include <algorithm>
#include <cstring>
#include <numeric>

static constexpr std::array<uchar, 256> get_init_state() noexcept
{
	std::array<uchar, 256> state{};
	std::iota(state.begin(), state.end(), 0);
	return state;
}

static const auto g_init_state = get_init_state();

RC4::RC4(int64 key) noexcept
{
	Init(key);
}

void RC4::Init(int64 key) noexcept
{
	m_state = g_init_state;
	m_x = 0;
	m_y = 0;

	ulong key_index = 0;
	ulong state_index = 0;
	const auto* key_ptr = reinterpret_cast<const uchar*>(&key);

	for (int16 i = 0; i < 256; ++i) {
		const ulong temp = m_state[i];
		state_index += key_ptr[key_index] + temp;
		state_index &= 0xFF;
		m_state[i] = m_state[state_index];
		m_state[state_index] = static_cast<uchar>(temp);
		key_index++;
		key_index &= 7;
	}
}

void RC4::Cypher(uchar* data, int32 length) noexcept
{
	uchar key1 = m_x;
	uchar key2 = m_y;

	for (int32 i = 0; i < length; ++i) {
		++key1;
		const uchar key_val1 = m_state[key1];

		key2 += key_val1;
		const uchar key_val2 = m_state[key2];

		m_state[key1] = key_val2;
		m_state[key2] = key_val1;

		data[i] ^= m_state[(key_val1 + key_val2) & 0xFF];
	}

	m_x = key1;
	m_y = key2;
}