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

typedef struct bitmap {
  int x;
  int y;
  unsigned char* pixels;
} BITMAP;

int mpi_self; /* process number */
int mpi_npes; /* number of process */
BITMAP picture; /* loaded picture */
int count; /* size of one part of work */


int read_bitmap(char* filename) {
  FILE* file;
  int readcount = 0;
  int size = 0;
  int i = 0;

  if ((file = fopen(filename, "rb")) == NULL) {
    printf("File %s not found!\n", filename);
    return 0;
  }

  fscanf(file, "%d %d", &picture.x, &picture.y);
  size = picture.x * picture.y;
  if (size == 0) {
    printf("File %s is not correct!\n", filename);
    fclose(file);
    return 0;
  }
  if ((size % mpi_npes) != 0) {
    count = ((size / mpi_npes) + 1) * mpi_npes;
  }
  else {
    count = size;
  }

  picture.pixels = (unsigned char*) malloc(count);

  readcount = fread(picture.pixels, 1, size, file);
  if (readcount != size) {
    printf("File %s is not correct!\n", filename);
    free((void*) picture.pixels);
    fclose(file);
    return 0;
  }

  for (i = 0; i < count - size; i++) {
    picture.pixels[size+i] = picture.pixels[0];
  }
  count = count / mpi_npes;

  fclose(file);
  return 1;
}


void write_bitmap(char* filename) {
  FILE* file;
  int size = 0;
  int i = 0;

  if ((file = fopen(filename, "wb")) == NULL) {
    printf("File %s can not be created!\n", filename);
  }
  else {
    fprintf(file, "%d %d", picture.x, picture.y);
    size = picture.x * picture.y;
    fwrite(picture.pixels, 1, size, file);
    free((void*) picture.pixels);
    printf("Successfully done.\n");
    fclose(file);
  }
}


void stretch_color(void) {
  int i;
  unsigned char min = 0;
  unsigned char max = 0;
  unsigned char lmin = 255;
  unsigned char lmax = 0;
  double konst = 0;
  unsigned char* work = NULL;

  /* everyone have to know how much to do*/
  MPI_Bcast(&count, 1, MPI_INT, 0, MPI_COMM_WORLD);
  work = (unsigned char*) malloc(count);

  /* send part of work */
  MPI_Scatter(picture.pixels, count, MPI_UNSIGNED_CHAR, work, 
              count, MPI_UNSIGNED_CHAR, 0, MPI_COMM_WORLD);

  /* compute local extrems */
  for (i = 0; i < count; i++) {
    if (work[i] < lmin) {
      lmin = work[i];
    }
    if (work[i] > lmax) {
      lmax = work[i];
    }
  }

  /* find out global extrems */
  MPI_Allreduce(&lmin, &min, 1, MPI_UNSIGNED_CHAR, MPI_MIN, MPI_COMM_WORLD);
  MPI_Allreduce(&lmax, &max, 1, MPI_UNSIGNED_CHAR, MPI_MAX, MPI_COMM_WORLD);

  /* stretch colors */
  konst = (255.0 / (max - min));
  for (i = 0; i < count; i++) {
    work[i] = (unsigned char) (((work[i] - min) * konst) + 0.5);
  }

  /* get whole picture */
  MPI_Gather(work, count, MPI_UNSIGNED_CHAR, picture.pixels,
              count, MPI_UNSIGNED_CHAR, 0, MPI_COMM_WORLD);

  free((void*) work);
}


int main (int argc, char *argv[]) {
  int ok = 0;

  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &mpi_self);
  MPI_Comm_size(MPI_COMM_WORLD, &mpi_npes);

  if (mpi_self == 0) {
    if (argc == 3) {
      ok = read_bitmap(argv[1]);    
    }
    else {
      printf("Incorrect number of arguments!\n");
      printf("Arguments are source file and destination file.\n");
    }
  }

  /* waiting for root to read picture */
  MPI_Bcast(&ok, 1, MPI_INT, 0, MPI_COMM_WORLD);

  if (ok) {
    stretch_color();
    if (mpi_self == 0) {
      write_bitmap(argv[2]);
    }
  }

  MPI_Finalize();
  return 0;
}