#include <algorithm>
#include <fstream>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_math.h>
#include <gsl/gsl_odeiv2.h>
#include <gsl/gsl_spline.h>
#include <iostream>
#include <numeric>
#include <string>
#include <stdexcept>
#include <vector>

#include "loadtxt.h"


extern "C" const int gsl_success() { return GSL_SUCCESS; } // It's zero, but just for clarity sake.

// Our units are {kiloparsec, solar mass, gigayear}
constexpr double G = 4.498317481097514e-06;

class Interp {
public:
    Interp(std::vector<double>& x, std::vector<double>& y)
    {
        acc    = gsl_interp_accel_alloc();
        spline = gsl_spline_alloc(gsl_interp_cspline, x.size());
        gsl_spline_init(spline, x.data(), y.data(), x.size()); 
    }
    Interp() {}
    inline double operator()(double x) const
    {
        return gsl_spline_eval(spline, x, acc);
    }

private:
    gsl_interp_accel *acc;
    gsl_spline *spline;
};

class Plummer {
public:
    Plummer(double M, double b)
        : M(M), b(b) {}
    void calc_acceleration(const double *pos, double *acc)
    {
        double r2 = (pos[0]*pos[0] + pos[1]*pos[1] + pos[2]*pos[2] + b*b);
        double r  = sqrt(r2);
        double r3_inv = 1/(r*r2);
        acc[0] = -G*M*pos[0]*r3_inv;
        acc[1] = -G*M*pos[1]*r3_inv;
        acc[2] = -G*M*pos[2]*r3_inv;
    }

private:
    double M, b;
};

class Galaxy {
public:
    Galaxy(std::string file_name)
    {
        auto data = Loadtxt("file.dat", {1, 2, 3}).get_cols();
        auto& t_data      = data[0];
        auto& halo_m_data = data[1];
        auto& halo_b_data = data[2];
        std::transform(t_data.begin(), t_data.end(), t_data.begin(), [](const double& x){ return x-2.145; });
        std::transform(halo_b_data.begin(), halo_b_data.end(), halo_b_data.begin(), [](const double& x){ return x*0.7664209365408798; });
        interp_halo_m = Interp(t_data, halo_m_data);
        interp_halo_b = Interp(t_data, halo_b_data);
    }
    int func(double t, const double y[], double f[], void *params)
    {
        double halo_m = interp_halo_m(t);
        double halo_b = interp_halo_b(t);
        Plummer plummer(halo_m, halo_b);
        f[0] = y[3]; // vx -> x'
        f[1] = y[4]; // vy -> y'
        f[2] = y[5]; // vz -> z'
        plummer.calc_acceleration(y, f+3); // a -> v'
        return GSL_SUCCESS;
    }

private:
    Interp interp_halo_m;
    Interp interp_halo_b;
} galaxy("file.dat");
// Not very nice to have it as a global variable but GSL will have problem otherwise.

int jac(double t, const double y[], double *dfdy, double dfdt[], void *params) { return GSL_SUCCESS; }

inline int func(double t, const double y[], double f[], void *params)
{
    return galaxy.func(t, y, f, params);
}

extern "C"
int integrate(const double y0[], const double t_max, const double step_size, double y[])
{
    double t = 0;
    constexpr double h = 1./4096.;

    if (step_size/h - (int)(step_size/h) != 0) throw std::runtime_error("step_size must be a multiple of h");
    constexpr double epsabs = 1e-7;
    constexpr double epsrel = 0;
    const gsl_odeiv2_step_type *T = gsl_odeiv2_step_rk8pd;
    gsl_odeiv2_step *s    = gsl_odeiv2_step_alloc(T, 6);
    gsl_odeiv2_evolve *e  = gsl_odeiv2_evolve_alloc(6);
    gsl_odeiv2_control *c = gsl_odeiv2_control_y_new(epsabs, 0);
    gsl_odeiv2_system sys = {func, jac, 6, nullptr};
    gsl_odeiv2_driver *d  = gsl_odeiv2_driver_alloc_y_new(&sys, T, h, epsabs, epsrel);

    int step = 0;
    const int step_max = t_max / step_size;
    std::copy(y0, y0+6, y);
    for (int step=0; step<step_max; step++) {
        std::copy(y+step*6, y+(step+1)*6, y+(step+1)*6);
        int status = gsl_odeiv2_driver_apply(d, &t, (step+1)*step_size, y+(step+1)*6);
        if (status != GSL_SUCCESS) return status;
    }
    return GSL_SUCCESS;
}

int main()
{
    std::cout << "bye" << std::endl;
    double y[12];
    double y0[] = {80,0,0,0,80,0};
    for (int i=0; i<30000; i++)
        integrate(y0, 10, 10, y);
    return 0;
}