//build: gcc ani2png.c -o ani2png

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

void ReadFile(char *name);
int teststring(char *buffer, int start);

int main(int argc, char **argv)
{
  if (argc != 2)
  {
    fprintf(stderr, "Usage: ani2png /path.ani");
    return 0;
  }
  ReadFile(*(argv + 1));
  return 0;
}

int teststring(char *buffer, int start)
{
  if (*(buffer + start) == 0x69)
  {
    if (*(buffer + start + 1) == 0x63)
    {
      if (*(buffer + start + 2) == 0x6f)
      {
        if (*(buffer + start + 3) == 0x6e)
        {
          return 1;
        }
      }
    }
  }
  else
    return 0;
}

void ReadFile(char *name)
{
  FILE *file;
  char *buffer, *fileName;
  unsigned long fileLen;

  if (!strstr(name, ".ani"))
  {
    fprintf(stderr, "Usage: ani2png /path.ani");
    return;
  }

  fileName = malloc(strlen(name) + 1);
  strcpy(fileName, name);
  *strstr(fileName, ".ani") = '\0';

  file = fopen(name, "rb");

  fseek(file, 0, SEEK_END);
  fileLen = ftell(file);
  fseek(file, 0, SEEK_SET);

  buffer = (char *)malloc(fileLen + 1);

  fread(buffer, fileLen, 1, file);
  fclose(file);

  char *new_png_name = malloc(strlen(name) + 5);

  char png_counter_string[5];
  int i, j, png_counter = 1;
  FILE *png_image;

  for (i = 0; i <= fileLen; i++)
  {
    if (png_counter == 9999)
    {
      free(fileName);
      free(buffer);
      free(new_png_name);
      return;
    }

    if ((i + 4 <= fileLen) && teststring(buffer, i) == 1)
    {
      sprintf(png_counter_string, "%d", png_counter);
      strcpy(new_png_name, fileName);
      strcat(new_png_name, png_counter_string);
      strcat(new_png_name, ".png");
      png_counter++;

      png_image = fopen(new_png_name, "wb");
      if (!png_image)
      {
        fprintf(stderr, "Unable to open file %s.\n", new_png_name);
        free(fileName);
        free(buffer);
        free(new_png_name);
        return;
      }

      j = 8;
      while (i + j + 4 <= fileLen)
      {
        if (teststring(buffer, i + j + 1) == 1)
          break;
        if (j == 10)
          putc(0x01, png_image);
        else
          putc(*(buffer + i + j), png_image);
        j++;
      }
      if (i + j <= fileLen)
        putc(*(buffer + i + j), png_image);
      if (fileLen - i - j <= 3)
      {
        putc(*(buffer + i + j + 1), png_image);
        putc(*(buffer + i + j + 2), png_image);
      }
      fclose(png_image);
      i += j;
    }
  }

  free(new_png_name);
  free(buffer);
  free(fileName);
}