#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

struct imghead_t {
  char *filename;
  int *els;
};

void printel(struct imghead_t *img, char *el, char **elnames, int numels);
int readhead(char *file, struct imghead_t *img, int *sizes, int numels);
void printhead(struct imghead_t *img, char **elnames, int numels);

int main(int argc, char **argv) {
  struct imghead_t myheader;
  int rc, i;

  /* info about bmp image header */
  int bmpnumels = 16;
  char *bmpelnames[16] = {"sig", "sizefile", "res1", "res2", "imgoffset", "sizehead", "width", "height", "numplanes", "bpp", "comptype", "sizedata", "hres", "vres", "numcols", "numicols"};
  int bmpsizes[16] = {2,4,2,2,4,4,4,4,2,2,4,4,4,4,4,4};
 
  if (argc < 2) {
    printf("USAGE: %s <bmpfile>\n", argv[0]);
    exit(1);
  }

  rc = readhead(argv[1], &myheader, bmpsizes, bmpnumels);
  if (!rc) {
    exit(1);
  }

  printhead(&myheader, bmpelnames, bmpnumels);

  exit(0);
}

void printhead(struct imghead_t *img, char **imgelnames, int numels) {
  int i;

  printf("Header Info for %s\n------------------\n", img->filename);

  for (i=0; i<numels; i++) {
    printel(img, imgelnames[i], imgelnames, numels);
  }

}

void printel(struct imghead_t *img, char *el, char **imgelnames, int numels) {
  int i;


  for (i=0; i<numels; i++) {
    if (!strcmp(imgelnames[i], el)) {
      printf("%s: %d\n", imgelnames[i], img->els[i]);
      break;
    }
  }

}

int readhead(char *file, struct imghead_t *img, int *imgsizes, int numels) {
  int rc, i, fd;

  img->filename = (char *)strdup(file);
  fd = open(file, O_RDONLY);
  if (fd < 0) {
    printf("ERROR: cannot open file %s\n", file);
    return(0);
  }
  
  img->els = (int *)malloc(sizeof(int) * numels);
  for (i=0; i<numels; i++) {
    img->els[i] = 0;
    rc = read(fd, &img->els[i], imgsizes[i]);  
    if (rc < imgsizes[i]) {
      printf("ERROR: corrupt img header\n");
      return(0);
    }
  }
  close(fd);
  
  return(1);
}