#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct bmp_header bmp_header;
struct bmp_header {
  uint8_t id[2];
  uint8_t size[4];
  uint8_t r1[2];
  uint8_t r2[2];
  uint8_t offset[4];
};

int32_t little_endian(uint8_t bytes[4]) {
  int32_t le = bytes[0] | (bytes[1] << 8) | (bytes[2] << 16) | (bytes[3] << 24);
  return le;
}

int main(int argc, char **argv) {
  if (argc != 2) {
    fprintf(stderr, "extractor [usage]: input_file");
    return EXIT_FAILURE;
  }
  bmp_header header;
  char search;
  int count = 0;
  char out_name[128] = {0};

  char *in = argv[1];
  FILE *fin = fopen(in, "r");
  fseek(fin, 0, SEEK_SET);
  while (fread(&search, sizeof(char), 1, fin) > 0) {
    if (search != 'B')
      continue;
    if (fread(&search, sizeof(char), 1, fin) <= 0)
      continue;
    if (search != 'M')
      continue;
    fpos_t pos;
    fseek(fin, -2 * sizeof(char), SEEK_CUR);
    fgetpos(fin, &pos);
    fread(&header, sizeof(bmp_header), 1, fin);
    if (header.r1[0] == 0 && header.r1[1] == 0 && header.r2[0] == 0 &&
        header.r2[1] == 0) {
      fseek(fin, pos, SEEK_SET);
      int32_t size = little_endian(header.size);
      char *data = (char *)malloc((size + 1) * sizeof(char));
      fread(data, sizeof(char), size, fin);
      data[size + 1] = 0;
      snprintf(out_name, sizeof out_name, "%s_%d.bmp", in, ++count);
      FILE *fout = fopen(out_name, "w");
      fwrite(data, sizeof(char), size, fout);
      fclose(fout);
      free(data);
    }
  }

  fclose(fin);
  return EXIT_SUCCESS;
}