#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <mpi.h>
#include "MPI1.h"
using namespace std;

int num_procs, my_proc; //These let you know how many processes there are, and what your specific process number is in this execution.
MPI_Request r;
MPI_Status status;

int main (int argc, char **argv) {

    MPI_Init (&argc,&argv); //This initializes MPI
    MPI_Comm_size (MPI_COMM_WORLD,&num_procs); //gets me the total number of processors
    MPI_Comm_rank (MPI_COMM_WORLD,&my_proc); //gets me my process number
    if (num_procs != 2) {
     if (my_proc==0) cout << "Error:  You must run with exactly two processors!" << endl;
    } else {
        if (my_proc==0) {
            cout << "Enter a string:  ";
            string str;
            getline (cin,str);
            cout << my_proc << " is sending:  \"" << str << "\"." << endl;
            const char *A = str.c_str(); //A is a pointer to the char array held in str
            MPI_Isend (A,strlen(A)+1,MPI_CHAR,1,42,MPI_COMM_WORLD,&r);
            //non-blocking send command.  The message will not send until the receiveding process
            //is ready to receive it...but this process will not have to wait around until the other process is ready
            //Parameters:  Pointer to the A.  Size of message, the type of data (I always use MPI_CHAR), the receiving process,
            //the message tag, the next parameters is always MPI_COMM_WORLD, and the parameter will hold return
            //status information from this method call
        } else {
            char A[100];
            MPI_Recv (A, sizeof A,MPI_CHAR,0,42,MPI_COMM_WORLD,&status);
            /*
            This is a "blocking receive" command.  It will wait until it receives a message.
            Parameters:  address of buffer, size of buffer, data type, who I'm receiving from, the message tag, MPI_COMM_WORLD,
            and status information returned by the message call.
             
            char A[100]; sizeof A yields 100.
            char *A = new char[100]; sizeof A yields 4.
            */

            string str (A);
            cout << "Process " << my_proc << " received the following transmission:  \"" << str << "\"." << endl;
        }
    }
    MPI_Finalize (); //clean everything up
    return 0;
}