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

#define NUM_ELEMS 60
#define NUM_PROCS 4
#define NUM_ELEM_PER_PROC 15
#define TAG_X 1
#define TAG_Y 2


int sendBuff[NUM_ELEMS];
int recvBuff[NUM_ELEM_PER_PROC];

int sum_node(int buf[NUM_ELEM_PER_PROC]){
	int partial_sum = 0;
	for (int k = 0; k < NUM_ELEM_PER_PROC; k++) {
		partial_sum += buf[k];
	}	
	return partial_sum;
}

int main(int argc, char **argv) {
	
	int myRank;
	MPI_Status status;

	int sum = 0;

	MPI_Init(&argc, &argv);
	MPI_Comm_rank(MPI_COMM_WORLD, &myRank);
	
	if (myRank == 0) {
		//master
		double startTime = MPI_Wtime();
		int i;
		for (i = 0; i < NUM_ELEMS; i++)
			sendBuff[i] = i+1;

		int j;
		for (j = 1; j < NUM_PROCS; j++) {
			int startIndex = j * NUM_ELEM_PER_PROC;
			int endIndex = startIndex + NUM_ELEM_PER_PROC;

			MPI_Send(&sendBuff[startIndex], NUM_ELEM_PER_PROC, MPI_INT, j, TAG_X, MPI_COMM_WORLD);	
		}

		int partial_sum = 0;
		for (j = 1; j < NUM_PROCS; j++) {
			MPI_Recv(&partial_sum, 1, MPI_INT, j, TAG_Y, MPI_COMM_WORLD, &status);
			sum += partial_sum;
		}

		sum += sum_node(sendBuff);
		double endTime = MPI_Wtime();

		//endTime - startTime
		printf("Grand sum = %d, and it took %f\n", sum, (endTime - startTime));

	} else {
		MPI_Recv(&recvBuff, NUM_ELEM_PER_PROC, MPI_INT, 0, TAG_X, MPI_COMM_WORLD, &status);

		int k;
		int partial_sum = sum_node(recvBuff);

		MPI_Send(&partial_sum, 1, MPI_INT, 0, TAG_Y, MPI_COMM_WORLD);

	}


	MPI_Finalize();

	return 0;
}