#include <chrono>
#include <cmath>
#include <cstdlib>
#include <fstream>
#include <iostream>
#include <mpi.h>

namespace
{
   void write_vector(int rank, int size, double* content, size_t content_size, char* fname)
   {
      for(int i = 0; i < rank; i++) MPI_Barrier(MPI_COMM_WORLD);
      
      // open the filestream
      std::ofstream target;
      if(rank) target.open(fname, std::ios_base::app);  // append to file
      else target.open(fname);  // create new file

      for(size_t i = 0; i < content_size; i++)
         target << content[i] << "\t";
      target << "\n";
      
      // close filestream so that the next process can write into the file
      target.close();
      
      for(int i = rank; i < size; i++) MPI_Barrier(MPI_COMM_WORLD);
   }
   
   // missing code
   // normalize the vector, taken together over all processes, so that it becomes a unit vector
   //
   void normalize_vector(int size, int rank, double* content, size_t content_size, MPI_Comm comm)
   {
   }
}

int main(int argc, char** argv)
{
   // we need at least one command-line argument, argc >= 2
   if(argc < 2) return EXIT_FAILURE;  
   
   MPI_Init(&argc, &argv);
   
   // how many processes are there?
   int size = 0;  
   MPI_Comm_size(MPI_COMM_WORLD, &size); 
   
   // what is the rank of this process?
   int rank = 0;
   MPI_Comm_rank(MPI_COMM_WORLD, &rank); 
   
   // how many random numbers are we generating per process?
   int dim_per_rank = std::atoi(argv[1]);
   if(0 >= dim_per_rank)
   {
      MPI_Finalize();
      return EXIT_FAILURE;  
   }
   
   // locally create part of the vector
   double* local_vector = new double[dim_per_rank];  
   
   // random seed from chrono
   std::srand(
      std::chrono::duration_cast<std::chrono::nanoseconds>(
         std::chrono::high_resolution_clock::now().time_since_epoch()
      ).count()
   );
   
   // fill local vector with random values between 0 and 1
   for(size_t i = 0; i < dim_per_rank; i++)
      local_vector[i] = (double)std::rand() / RAND_MAX;
   
   // missing operation: normalize the vector so that it becomes a unit vector
   //
   normalize_vector(size, rank, local_vector, dim_per_rank, MPI_COMM_WORLD);
   
   if(argc >= 3)
   {
      if(!rank) std::cout << "writing to file '" << argv[2] << "'.\n";
      
      write_vector(rank, size, local_vector, dim_per_rank, argv[2]);
   }
   
   delete[] local_vector;
   MPI_Finalize();
}