#include <iostream>
#include <mpi.h>

using namespace std;

const int ROUNDS{10};

void TossTheBallRandom(int value, int  rank, int  size);
void TossTheBall(int value, bool &finished, int rank, int size);
void GetMessage(int & value, bool & finished, int rank, int size);

// some custom tags
const int BALL_PASS{1};
const int EXIT_PASS{2};

int main(int argc, char * argv[]) {
   MPI_Init(&argc, &argv);

   int value{0};
   bool finished{false};

   int rank, size;
   MPI_Comm_rank(MPI_COMM_WORLD, &rank);
   MPI_Comm_size(MPI_COMM_WORLD, &size);

   srand(time(nullptr) * (rank+1));

   // rank 0 starts off by throwing the ball to everyone.
   if (rank == 0) {
       TossTheBallRandom(value, rank, size);
   } 

   while (not finished) {
       GetMessage(value, finished, rank, size);
       TossTheBall(value, finished, rank, size);
   }

   if (rank == 0) {
      for(int i = 1; i < size; ++i) {
         cout << rank  << " sending an exit to " << i << endl;
         MPI_Send(&value, 0, MPI_INT, i, EXIT_PASS, MPI_COMM_WORLD); 
      }
   }

   MPI_Finalize();
   return 0;
}

void GetMessage(int & value, bool & finished, int rank, int size){
   MPI_Status status;
   int tmp;

   MPI_Probe(MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);

   cout << endl;
   cout << "\t\tThe message came from " << status.MPI_SOURCE << endl;
   cout << "\t\tThe message had tag " << status.MPI_TAG << endl;
   int count;
   MPI_Get_count(&status, MPI_INT, &count);
   cout << "\t\tThe message had " << count << " integers " << endl;
   cout << endl;

   if (status.MPI_TAG == EXIT_PASS) {
       MPI_Recv(&tmp, 0, MPI_INT, MPI_ANY_SOURCE, EXIT_PASS,
                MPI_COMM_WORLD, &status);

       finished = true;

       cout << "\t" << rank << " got an exit " << endl;

   } else {

       MPI_Recv(&value, 1, MPI_INT, MPI_ANY_SOURCE, BALL_PASS, 
                  MPI_COMM_WORLD, &status);

       cout << "\t" << rank  << " got "  << value 
            << " from " << status.MPI_SOURCE << endl;
   }
}

void TossTheBall(int value, bool &finished, int rank, int size) {

       if (value == ROUNDS) {
          if (rank != 0) {
              cout << rank << " Sending  " << value << " back to 0" << endl;
              MPI_Send (&value, 1, MPI_INT, 0, BALL_PASS, MPI_COMM_WORLD);

          } else {
              finished = true;
          }

       } else {
          TossTheBallRandom(value, rank, size);
       }
}

void TossTheBallRandom(int value, int  rank, int  size){
    int  dest = rand() % size;

    while (dest == rank) {
        dest = rand() % size;
    }

    ++value;

    cout << rank << " sending a " << value << " to " << dest << endl;
    MPI_Send (&value, 1, MPI_INT, dest, BALL_PASS, MPI_COMM_WORLD);
}