#include <vector>
#include <string>
#include <iostream> // std::cout
#include <fstream>  // ifstream, ofstream
#include <libgen.h> // basename()
#include <iterator>

using namespace std;

string filePath = "";
vector<unsigned char> buffer;

int desp = 0x2000;
int numBytes = 0x2000;
int firstByte = desp + 0x200;
int lastByte = desp + numBytes - 1;
int checksum1 = desp + 0x270;
int checksum2 = desp + 0x271;

void checkParameters(int argc, char *argv[])
{
    if (argc != 2)
    {
        cout << "Uso: " << basename(argv[0]) << " FILE" << endl;
        exit(EXIT_FAILURE);
    }
    else
        filePath = argv[1];
}

void loadFile(string s)
{
    ifstream inputFile(s, ios::binary);
    if (inputFile.good())
        buffer.assign(istreambuf_iterator<char>(inputFile), {});
    else
    {
        cout << "No se puede abrir el archivo: " << s << endl;
        exit(EXIT_FAILURE);
    }
    inputFile.close();
}

void saveFile(string s)
{
    ofstream outputFile(s, ios::binary);
    if (outputFile.good())
    {
        for (auto i : buffer)
        {
            outputFile << i;
        }
        cout << "Fichero guardado: " << s << endl;
    }
    else
    {
        cout << "No se puede abrir el archivo: " << s << endl;
        exit(EXIT_FAILURE);
    }
    outputFile.close();
}

void printBuffer()
{
    int count = 0;
    for (auto i : buffer)
    {
        cout << static_cast<unsigned>(i) << " ";
        count++;
        if (count % 16 == 0)
            cout << static_cast<unsigned>(i) << endl;
    }
}

int calcChecksum()
{
    int sum = 0;
    for (int i = firstByte; i <= lastByte; i++)
    {
        if (i != checksum1 and i != checksum2)
            sum += static_cast<unsigned>(buffer.at(i));
    }
    sum += 3328; // Corrige el checksum
    buffer.at(checksum1) = sum % 256;
    buffer.at(checksum2) = (sum >> 8) % 256;
    return sum;
}

int main(int argc, char *argv[])
{
    checkParameters(argc, argv);
    loadFile(filePath);
    int sum = calcChecksum();
    saveFile(filePath);

    cout << hex;
    cout << "0x" << checksum1 << ": 0x" << static_cast<unsigned>(buffer.at(checksum1)) << endl;
    cout << "0x" << checksum2 << ": 0x" << static_cast<unsigned>(buffer.at(checksum2)) << endl;
    cout << "checksum (0x" << firstByte << " .. 0x" << lastByte << "): 0x" << sum << endl;

    return 0;
}