// ==================================================================
// Author: Jean-Michel Richer
// Date: Aug 2020
// Last modified: November 2020
// Purpose: Use of MPI::Gather
// Each process creates its own local vector of data and they are all
// sent to the master process (of rank 0)
// ==================================================================
#include <unistd.h>
#include <unistd.h>  // for sleep

#include <cstdlib>
#include <iostream>
#include <numeric>
#include <sstream>
#include <vector>
using namespace std;
#include "ezmpi.hpp"
using namespace ez::mpi;

/**
 * run master and slaves
 */
void run(int argc, char* argv[]) {
    Process process(argc, argv);

    // --------------------------------------------------------------
    // declaration of data
    // --------------------------------------------------------------

    // this is for the master
    vector<int> big_vec;

    // this is for the master and the slaves
    int local_vec_size = 10;
    vector<int> local_vec(local_vec_size);

    // depending on the process fill the local vector with numbers
    iota(local_vec.begin(), local_vec.end(), process.id() * 10 + 1);

    process << "- local vector=" << local_vec << endl;

    if (process.is_master()) {
        // master process will gather data from others
        // so define the size of the vector that will
        // receive other data from the slaves and
        // fill it with 0's
        big_vec.resize(process.nbr_processes() * local_vec_size, 0);
    }

    // gather data from all processes to master
    // note: this must be executed by all processes
    process.gather(local_vec.data(), local_vec_size, big_vec.data());

    // finally print the content of the big vector on the master
    if (process.is_master()) {
        process << "- big vector = " << big_vec << endl;
    }

    process.logs(cout);
}

// ==================================================================
// C++ version
// ==================================================================
int main(int argc, char** argv) {
    // call a function that contains the code for the master and
    // the slaves in order to avoid problems of initialization and
    // finalization of processes
    run(argc, argv);

    exit(EXIT_SUCCESS);
}