// Copyright 2017 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#include <cstring>

#include "core/hle/service/nwm/nwm_uds.h"
#include "core/hle/service/nwm/uds_data.h"
#include "core/hw/aes/key.h"

#include <cryptopp/aes.h>
#include <cryptopp/md5.h>
#include <cryptopp/modes.h>

namespace Service {
namespace NWM {

// AES Keyslot used to generate the UDS data frame CCMP key.
constexpr size_t UDSDataCryptoAESKeySlot = 0x2D;

/*
 * Generates a SNAP-enabled 802.2 LLC header for the specified protocol.
 * @returns a buffer with the bytes of the generated header.
 */
static std::vector<u8> GenerateLLCHeader(EtherType protocol) {
    LLCHeader header{};
    header.protocol = static_cast<u16>(protocol);

    std::vector<u8> buffer(sizeof(header));
    memcpy(buffer.data(), &header, sizeof(header));

    return buffer;
}

/*
 * Generates a Nintendo UDS SecureData header with the specified parameters.
 * @returns a buffer with the bytes of the generated header.
 */
static std::vector<u8> GenerateSecureDataHeader(u16 data_size, u8 channel, u16 dest_node_id,
    u16 src_node_id, u16 sequence_number) {
    SecureDataHeader header{};
    header.protocol_size = data_size + sizeof(SecureDataHeader);
    // Note: This size includes everything except the first 4 bytes of the structure,
    // reinforcing the hypotheses that the first 4 bytes are actually the header of
    // another container protocol.
    header.securedata_size = data_size + sizeof(SecureDataHeader) - 4;
    header.is_management = 0; // Frames sent by the emulated application are never UDS management frames
    header.data_channel = channel;
    header.sequence_number = sequence_number;
    header.dest_node_id = dest_node_id;
    header.src_node_id = src_node_id;

    std::vector<u8> buffer(sizeof(header));
    memcpy(buffer.data(), &header, sizeof(header));

    return buffer;
}

/*
 * Calculates the CTR used for the AES-CTR process that calculates
  * the CCMP crypto key for data frames.
 * @returns The CTR used for data frames crypto key generation.
 */
static std::array<u8, CryptoPP::MD5::DIGESTSIZE> GetDataCryptoCTR(const NetworkInfo& network_info) {
    DataFrameCryptoCTR data{};

    data.host_mac = network_info.host_mac_address;
    data.wlan_comm_id = network_info.wlan_comm_id;
    data.id = network_info.id;
    data.network_id = network_info.network_id;

    std::array<u8, CryptoPP::MD5::DIGESTSIZE> hash;
    CryptoPP::MD5().CalculateDigest(hash.data(), reinterpret_cast<u8*>(&data), sizeof(data));

    return hash;
}

/*
 * Generates the key used for encrypting the 802.11 data frames generated by UDS.
 * @returns The key used for data frames crypto.
 */
static std::array<u8, CryptoPP::AES::BLOCKSIZE> GenerateDataCCMPKey(const std::vector<u8>& passphrase,
    const NetworkInfo& network_info) {
    // Calculate the MD5 hash of the input passphrase.
    std::array<u8, CryptoPP::MD5::DIGESTSIZE> passphrase_hash;
    CryptoPP::MD5().CalculateDigest(passphrase_hash.data(), passphrase.data(), passphrase.size());

    std::array<u8, CryptoPP::AES::BLOCKSIZE> ccmp_key;

    // The CCMP key is the result of encrypting the MD5 hash of the passphrase with AES-CTR using keyslot 0x2D.
    using CryptoPP::AES;
    std::array<u8, CryptoPP::MD5::DIGESTSIZE> counter = GetDataCryptoCTR(network_info);
    std::array<u8, AES::BLOCKSIZE> key = HW::AES::GetNormalKey(UDSDataCryptoAESKeySlot);
    CryptoPP::CTR_Mode<AES>::Encryption aes;
    aes.SetKeyWithIV(key.data(), AES::BLOCKSIZE, counter.data());
    aes.ProcessData(ccmp_key.data(), passphrase_hash.data(), passphrase_hash.size());

    return ccmp_key;
}

std::vector<u8> GenerateDataFrame(const std::vector<u8>& data, u8 channel, u16 dest_node, u16 src_node, u16 sequence_number) {
    std::vector<u8> buffer = GenerateLLCHeader(EtherType::SecureData);
    std::vector<u8> securedata_header = GenerateSecureDataHeader(data.size(), channel, dest_node, src_node, sequence_number);

    buffer.insert(buffer.end(), securedata_header.begin(), securedata_header.end());
    buffer.insert(buffer.end(), data.begin(), data.end());
    // TODO(Subv): Encrypt the frame.
    // TODO(Subv): Prepend CCMP initialization vector (sequence_number).
    // TODO(Subv): Encapsulate the frame in an 802.11 data frame.
    return buffer;
}

} // namespace NWM
} // namespace Service