#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <mpi.h>

 // Grouped Calculs program

int main(int argc, char** argv) 
{
	MPI_Init(NULL, NULL);
	int nb_mpi_processes;
	MPI_Comm_size(MPI_COMM_WORLD, &nb_mpi_processes);
	int rank;
	MPI_Comm_rank(MPI_COMM_WORLD, &rank);

	if(nb_mpi_processes != 2) { printf("This program is design to be run with 2 processes only"); return 0;}

	int Nx1=20;
	int Nx1l = Nx1/2;
	double * Field = malloc(Nx1l * sizeof(double));
	double * Field_buff = malloc(Nx1l * sizeof(double));
	int i;

	for(i = 0; i < Nx1l; ++i)
		Field[i] = 0.0;

	if(rank==1) {Field[2] = 1.0; Field[3]=2.0;}

	char fileName[2048];
	sprintf(fileName, "IN.%d.dat", rank);

	FILE *file = NULL;
	file = fopen(fileName, "w");
	for(i = 1; i < Nx1l-1; ++i)
		fprintf(file, "%d %d %lf\n", i, Field[i]);
	fclose(file);

	int niter=8;
	int n;
	int tag = 7777;
	for(n = 1; n <= niter; ++n) 
	{
		if(rank==0)
		{
			MPI_Sendrecv ( &Field[Nx1l-2] , 1 , MPI_DOUBLE , 1 , tag , &Field[Nx1l-1] , 1 , MPI_DOUBLE , 1 , tag , MPI_COMM_WORLD , MPI_STATUS_IGNORE);
		}
		if(rank==1)
		{
			MPI_Sendrecv ( &Field[1] , 1 , MPI_DOUBLE , 0 , tag, &Field[0] , 1 , MPI_DOUBLE , 0 , tag , MPI_COMM_WORLD , MPI_STATUS_IGNORE);
		}

		for(i = 1; i < Nx1l-1; ++i)
			Field_buff[i] = ( Field[i-1] + Field[i] + Field[i+1] ) / 3.0;

		for(i = 1; i < Nx1l-1; ++i)
			Field[i] =  Field_buff[i];
	}

	sprintf(fileName, "OUT.%d.dat", rank);
	file = fopen(fileName, "w");
	for(i = 1; i < Nx1l-1; ++i)
		fprintf(file, "%d %d %lf\n", i, Field[i]);
	fclose(file);

	MPI_Finalize();

	return 0;
}