#include <stdio.h>

#define MaxVertices 400000
#define MaxFaces    400000 
#define MaxGroups   100

float       vertex[MaxVertices*3];
unsigned int  face[MaxFaces*3];
char    group_name[MaxGroups][80];
int     start_face[MaxGroups];

int vertices = 0;
int faces    = 0;
int groups   = 0;

void read_wavefront(const char *filename)
{
  char line[80];
  FILE *f = fopen(filename, "r");
  while(fgets(line, sizeof(line), f))
    switch(line[0])
      {
      case 'v':
        sscanf(&line[1],  "%f %f %f", &vertex[vertices*3],
               &vertex[vertices*3+1], &vertex[vertices*3+2]);
        ++vertices;
        break;
      case 'g':
        sscanf(&line[1], "%s", group_name[groups]);
        start_face[groups++] = faces;
        break;
      case 'f':
        sscanf(&line[1],  "%d %d %d", &face[faces*3],
               &face[faces*3+1], &face[faces*3+2]);
        --face[faces*3]; --face[faces*3+1];
        --face[faces*3+2]; ++faces; 
        break;
      }
  fclose(f);
  start_face[groups] = faces;
  printf("Read %d vertices and %d faces within %d groups from %s\n",
         vertices, faces, groups, filename);
}

void write_wavefront(int group_number)
{
  int i = 0; char n[80], *p = group_name[group_number];
  while (*p != '%' && *p != '\0') n[i++] = *p++; // remove % from name
  n[i++] = '.'; n[i++] = 'o'; n[i++] = 'b'; n[i++] = 'j'; n[i] = '\0';
  FILE *f = fopen(n, "w"); fprintf(f, "# Wavefront OBJ file\n");
  for (i = 0; i < vertices; i++)
    fprintf(f, "v %g %g %g\n", vertex[i*3], vertex[i*3+1], vertex[i*3+2]);
  fprintf(f, "g %s\n", group_name[group_number]);
  for (i = start_face[group_number]; i < start_face[group_number+1]; ++i)
    fprintf(f, "f %d %d %d\n", face[i*3]+1, face[i*3+1]+1, face[i*3+2]+1);
  fclose(f);
}

int main(int argc, char **argv)
{
  int i;
  read_wavefront("motorBike.obj");
  for(i = 0; i < groups; i++) write_wavefront(i);
  return 0;
}