#include <iostream>
#include <vector>
#include <algorithm>
#include <random>
#include <chrono>
#include <string>
#include <stdexcept>
#include <cstdlib>

namespace chrono = std::chrono;

// Custom function to read command line arguments
std::pair<int, int> read_arguments(int argc, char *argv[]);

int compare_ip(void const *a, void const *b)
{
    return *(int const *)a - *(int const *)b;
}

/**
 * Read number of elements (N) from the command line, generate a
 * random vector of this size and sort it.
 * Repeat M times for statistics (M is the second command line argument).
 */
int main(int argc, char *argv[])
{
    // Read N and M from command line
    auto [N, M] = read_arguments(argc, argv);

    // Function for random number generation
    std::random_device entropy;
    std::mt19937 gen(entropy()); // Randomness generator.
    std::uniform_int_distribution<> dis(0, 1000*N);
    auto draw = [&gen, &dis] () { return dis(gen); };

    int *rnd_array = new int[N];

    // Time sorting M random arrays of N elements.
    double elapsed = 0;

    for (int j = 0; j < M; j++) {

        std::generate(rnd_array, rnd_array + N, draw);

        auto t1 = chrono::high_resolution_clock::now();

        qsort(rnd_array, N, sizeof(int), compare_ip);

        auto t2 = chrono::high_resolution_clock::now();

        auto dt = chrono::duration_cast<chrono::microseconds>(t2 - t1);
        elapsed += dt.count();
    }

    // Show timing resuts.
    std::cout << N << " " << elapsed/M/1e6 << std::endl;

}

std::pair<int, int> read_arguments(int argc, char *argv[])
{
    int N, M;

    // We need exactly three arguments (considering program name).
    if (argc != 3) {
        std::cout << "Usage: " << argv[0]
                  << " <number of elements> <number of arrays>\n";
        exit(1);
    }

    // Read arguments.
    try {
        N = std::stoi(argv[1]);
        M = std::stoi(argv[2]);
    }
    catch (std::invalid_argument &) {
        std::cerr << "Command line argument invalid: must be int.\n";
        exit(1);
    }
    catch (std::out_of_range &) {
        std::cerr << "Number too large or too small.\n";
        exit(1);
    }

    return {N, M};
}