/* Copyright (c) 2019, Anthony Latorre <tlatorre at uchicago>
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option)
 * any later version.

 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.

 * You should have received a copy of the GNU General Public License along with
 * this program. If not, see <https://www.gnu.org/licenses/>.
 */

#include <stdio.h>
#include <gsl/gsl_spline.h>
#include <stdlib.h> /* for size_t, strtod() */
#include <errno.h> /* for errno */
#include <string.h> /* for strerror(), strtok() */
#include "sno.h"

static double *x, *dEdx_rad, *dEdx, *csda_range;
static size_t size;

static gsl_interp_accel *acc_dEdx_rad;
static gsl_spline *spline_dEdx_rad;

static gsl_interp_accel *acc_dEdx;
static gsl_spline *spline_dEdx;

static gsl_interp_accel *acc_range;
static gsl_spline *spline_range;

static int init()
{
    int i, j;
    char line[256];
    char *str;
    double value;
    int n;

    FILE *f = fopen("e_water_liquid.txt", "r");

    if (!f) {
        fprintf(stderr, "failed to open e_water_liquid.txt: %s\n", strerror(errno));
        return -1;
    }

    i = 0;
    n = 0;
    /* For the first pass, we just count how many values there are. */
    while (fgets(line, sizeof(line), f)) {
        size_t len = strlen(line);
        if (len && (line[len-1] != '\n')) {
            fprintf(stderr, "got incomplete line on line %i: '%s'\n", i, line);
            goto err;
        }

        i += 1;

        /* Skip the first 8 lines since it's just a header. */
        if (i <= 8) continue;

        if (!len) continue;
        else if (line[0] == '#') continue;

        str = strtok(line," \n");

        while (str) {
            value = strtod(str, NULL);
            str = strtok(NULL," \n");
        }

        n += 1;
    }

    x = malloc(sizeof(double)*n);
    dEdx_rad = malloc(sizeof(double)*n);
    dEdx = malloc(sizeof(double)*n);
    csda_range = malloc(sizeof(double)*n);
    size = n;

    i = 0;
    n = 0;
    /* Now, we actually store the values. */
    rewind(f);
    while (fgets(line, sizeof(line), f)) {
        size_t len = strlen(line);
        if (len && (line[len-1] != '\n')) {
            fprintf(stderr, "got incomplete line on line %i: '%s'\n", i, line);
            goto err;
        }

        i += 1;

        /* Skip the first 8 lines since it's just a header. */
        if (i <= 8) continue;

        if (!len) continue;
        else if (line[0] == '#') continue;

        str = strtok(line," \n");

        j = 0;
        while (str) {
            value = strtod(str, NULL);
            switch (j) {
            case 0:
                x[n] = value;
                break;
            case 2:
                dEdx_rad[n] = value;
                break;
            case 3:
                dEdx[n] = value;
                break;
            case 4:
                csda_range[n] = value;
                break;
            }
            j += 1;
            str = strtok(NULL," \n");
        }

        n += 1;
    }

    fclose(f);

    acc_dEdx_rad = gsl_interp_accel_alloc();
    spline_dEdx_rad = gsl_spline_alloc(gsl_interp_linear, size);
    gsl_spline_init(spline_dEdx_rad, x, dEdx_rad, size);

    acc_dEdx = gsl_interp_accel_alloc();
    spline_dEdx = gsl_spline_alloc(gsl_interp_linear, size);
    gsl_spline_init(spline_dEdx, x, dEdx, size);

    acc_range = gsl_interp_accel_alloc();
    spline_range = gsl_spline_alloc(gsl_interp_linear, size);
    gsl_spline_init(spline_range, x, csda_range, size);

    return 0;

err:
    fclose(f);

    return -1;
}

double electron_get_dEdx(double T, double rho)
{
    /* Returns the approximate dE/dx for a electron in water with kinetic energy
     * `T`.
     *
     * `T` should be in MeV and `rho` in g/cm^3.
     *
     * Return value is in MeV/cm.
     *
     * See http://pdg.lbl.gov/2018/AtomicNuclearProperties/adndt.pdf. */
    if (T < spline_dEdx->x[0]) return spline_dEdx->y[0];

    return gsl_spline_eval(spline_dEdx, T, acc_dEdx)*rho;
}

int main(int argc, char **argv)
{
    int i;
    double T0, T, dx, range;

    init();

    dx = 1e-5;

    for (i = 0; i < size; i++) {
        T0 = x[i];

        T = T0;

        range = 0.0;
        while (T > 0) {
            double dEdx2 = electron_get_dEdx(T, WATER_DENSITY);
            T -= dEdx2*dx;
            range += dx;
        }

        printf("%.3E %.3E\n", T0, range);
    }

    return 0;
}