#include <algorithm>
#include <cstdlib>
#include <fstream>
#include <vector>

//TODO if cols is an empty vector, get all columns from the file
//TODO error checking

class Loadtxt {
public:
    Loadtxt(std::string file_name, std::vector<int> cols)
    {
        std::sort(cols.begin(), cols.end());
        n_cols = cols.size();
        const int tmp_number_of_rows = 16384;
        int n_rows_alloc = tmp_number_of_rows;
        buffer = (double*)malloc(n_cols * sizeof(double) * n_rows_alloc);
        std::ifstream file(file_name);
        std::string line;
        int row = -1;
        while (getline(file, line)) {
            if (line[line.find_first_not_of(whitespaces)]=='#') continue;
            if (++row >= n_rows_alloc) {
                n_rows_alloc += tmp_number_of_rows;
                buffer = (double*)realloc(buffer, n_cols * sizeof(double) * n_rows_alloc);
            }
            line_to_buf(cols, line, buffer + row*n_cols);
        }
        file.close();
        buffer = (double*)realloc(buffer, n_cols * sizeof(double) * (++row));
        n_rows = row;
    }
    ~Loadtxt()
    {
        free(buffer);
    }
    std::vector<std::vector<double>> get_cols()
    {
        std::vector<std::vector<double>> data(n_cols);
        for (int col=0; col<n_cols; col++) data[col] = std::vector<double>(n_rows);
        for (int row=0; row<n_rows; row++) {
            for (int col=0; col<n_cols; col++) {
                data[col][row] = buffer[row*n_cols + col];
            }
        }
        return data;
    }
private:
    const char *whitespaces = " \t";
    void line_to_buf(std::vector<int> cols, std::string line, double *buffer)
    {
        int n_cols = cols.size();
        line = line.substr(line.find_first_not_of(whitespaces));
        auto pos = line.find_first_of(whitespaces, 1);
        int col=0, idx=0;
        std::vector<double> data;
        while (pos != std::string::npos) {
            std::string num_as_string;
            num_as_string = line.substr(0, pos);
            pos = line.find_first_not_of(whitespaces, pos);
            line = line.substr(pos, std::string::npos);
            pos = line.find_first_of(whitespaces, 1);
            if (col++ == cols[idx]) buffer[idx++] = std::stod(num_as_string);
        }
        if (col++ == cols[idx]) buffer[idx++] = std::stod(line);
        if (idx < n_cols) throw;
    }
    double *buffer;
    int n_rows, n_cols;
};

// Below is a deomonstration. The file has multiple columns but we are only
// interested in the second and fourth. We pass the file name and the column
// vector {1, 3} (since numbering starts at zero) and immediately call the
// get_cols() member, which returns a vector of vectors. We then manually assign
// the data members into named vectors.
//
// #include <iostream>
// int main()
// {

//     auto data = Loadtxt("file.dat", {1, 3}).get_cols();
//     auto& time  = data[0];
//     auto& value = data[1];
//     for (size_t i=0; i<time.size(); i++) {
//         std::cout << "time: " << time[i] << "   value: " << value[i] << std::endl;
//     }
// }