// my_rgamma - generate random variates from the gamma distribution
//             a demo of the R standalone math library
//
// Written in 2020 by Charles J. Geyer <geyer@umn.edu>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// See the CC0 Public Domain Dedication
// <http://creativecommons.org/publicdomain/zero/1.0/>.

#define MATHLIB_STANDALONE
#include <Rmath.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <sys/random.h>

// The immediately preceding include and the call to getrandom
// to initialize RNG are linux-specific
// Must do something else on other OS.

int main(int argc, char *argv[])
{
    if (argc != 4) {
        fputs("Usage: my_rgamma n alpha beta\n"
            "where n is a positive integer and alpha and beta"
            " are postive real numbers\n"
            "the shape and scale parameters (respectively)\n", stderr);
        return EXIT_FAILURE;
    }

    unsigned int n;
    double alpha, beta;

    if (sscanf(argv[1], "%u", &n) != 1) {
        fputs("failed to read x\n", stderr);
        return EXIT_FAILURE;
    }

    if (sscanf(argv[2], "%lg", &alpha) != 1) {
        fputs("failed to read alpha\n", stderr);
        return EXIT_FAILURE;
    }

    if (sscanf(argv[3], "%lg", &beta) != 1) {
        fputs("failed to read beta\n", stderr);
        return EXIT_FAILURE;
    }

    unsigned int seed1, seed2;
    size_t buflen = sizeof(unsigned int);

    if (getrandom(&seed1, buflen, GRND_RANDOM) != (ssize_t) buflen ||
        getrandom(&seed2, buflen, GRND_RANDOM) != (ssize_t) buflen) {
        fputs("failed to initialize random number generator\n", stderr);
        return EXIT_FAILURE;
    }

    set_seed(seed1, seed2);

    for (unsigned int i = 0; i < n; i++)
        printf("%12.10f\n", rgamma(alpha, beta));

    return EXIT_SUCCESS;
}