#include <stdio.h>
#include "mpi.h"
#include "trap.h"
typedef struct {
    float a;
    float b;
    int n;
}  INDATA_TYPE;
void Build_derived_type(INDATA_TYPE* indata,
    MPI_Datatype* message_type_ptr){
    int block_lengths[3];
    MPI_Aint displacements[3];
    MPI_Aint addresses[4];
    MPI_Datatype typelist[3];
    typelist[0] = MPI_FLOAT;
    typelist[1] = MPI_FLOAT;
    typelist[2] = MPI_INT;
    block_lengths[0] = block_lengths[1] =  block_lengths[2] = 1;
    MPI_Address(indata, &addresses[0]);
    MPI_Address(&(indata->a), &addresses[1]);
    MPI_Address(&(indata->b), &addresses[2]);
    MPI_Address(&(indata->n), &addresses[3]);
    displacements[0] = addresses[1] - addresses[0];
    displacements[1] = addresses[2] - addresses[0];
    displacements[2] = addresses[3] - addresses[0];
    MPI_Type_struct(3, block_lengths, displacements, typelist,message_type_ptr);
    MPI_Type_commit(message_type_ptr);
}

void Get_data3(int me, INDATA_TYPE* indata){
    MPI_Datatype message_type; 
    int root = 0, count = 1; 
    if (me == 0){
      printf("Enter a, b, and n\n");
      scanf("%f %f %d", &(indata->a), &(indata->b), &(indata->n));
    }
    Build_derived_type(indata, &message_type);
    MPI_Bcast(indata, count, message_type, root, MPI_COMM_WORLD);
} 

int main(int argc, char** argv) {
    int me, nproc, local_n;          
    float h, local_a, local_b, integral, total;         
    INDATA_TYPE indata;
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &me);
    MPI_Comm_size(MPI_COMM_WORLD, &nproc);
    Get_data3(me, &indata);
    h = (indata.b-indata.a)/indata.n; 
    local_n = indata.n/nproc; 
    local_a = indata.a + me*local_n*h;
    local_b = local_a + local_n*h;
    integral = Trap(local_a, local_b, local_n, h);
    MPI_Reduce(&integral, &total, 1, MPI_FLOAT, MPI_SUM, 0, MPI_COMM_WORLD);
    if(me == 0) {
      printf("With n = %d trapezoids, our estimate\n", indata.n);
      printf("of the integral from %f to %f = %f\n", 
             indata.a, indata.b, total); 
    }
    MPI_Finalize();
    return 0;
}