/* akyuu.c - Don Yang (uguu.org)

   09/07/08
                                                                           */
/*@ -compdef -usedef @*/

#include<stdio.h>
#include<string.h>
#ifdef _WIN32
   #include<io.h>
   #include<fcntl.h>
#endif

#define READ_BUFFER_SIZE   10000
#define WRITE_BUFFER_SIZE  8000

/* Decode a 5 character block */
#define BASE 90
#define DECODE_BLOCK \
   e = (unsigned int)(*r++) - 33;                                       \
   d = (unsigned int)(*r++) - 33;                                       \
   c = (unsigned int)(*r++) - 33;                                       \
   b = (unsigned int)(*r++) - 33;                                       \
   a = (unsigned int)(*r++) - 33;                                       \
   output_word = (((a * BASE + b) * BASE + c) * BASE + d) * BASE + e;   \
   *w++ = (unsigned char)(output_word & 255);                           \
   *w++ = (unsigned char)((output_word >>= 8) & 255);                   \
   *w++ = (unsigned char)((output_word >>= 8) & 255);                   \
   *w++ = (unsigned char)(output_word >> 8);

/* Decode file to stdout */
static void Decode(FILE *infile)
{
   unsigned char input[READ_BUFFER_SIZE];
   unsigned char output[WRITE_BUFFER_SIZE];
   unsigned char *r, *w;
   unsigned int output_word, a, b, c, d, e;
   size_t read_size, offset, block_count;

   offset = 0;
   while( (read_size = fread(input + offset, 1,
                             READ_BUFFER_SIZE - offset, infile)) > 0 )
   {
      /* Skip over illegal characters in input */
      read_size += offset;
      for(r = w = input + offset; r < input + read_size; r++)
      {
         if( (unsigned int)*r >= 33 && (unsigned int)*r < 33 + BASE )
            *w++ = *r;
      }
      read_size = (size_t)w - (size_t)input;

      /* Convert input */
      r = input;
      w = output;
      block_count = read_size / 5;
      for(offset = 0; offset < block_count; offset++)
      {
         DECODE_BLOCK
      }

      /* Write output */
      (void)fwrite(output, (size_t)w - (size_t)output, 1, stdout);

      /* Shift last incomplete block */
      offset = read_size % 5;
      if( offset > 0 )
         memmove(input, r, offset);
   }

   /* Write last incomplete block */
   if( offset > 0 )
   {
      for(a = (unsigned int)offset; a < 5; a++)
         input[a] = (unsigned char)33;
      r = input;
      w = output;
      DECODE_BLOCK
      (void)fwrite(output, offset - 1, 1, stdout);
   }
}

int main(int argc, char **argv)
{
   FILE *infile;

   #ifdef _WIN32
      setmode(fileno(stdout), O_BINARY);
   #endif
   if( argc < 2 )
   {
      Decode(stdin);
   }
   else if( argc == 2 )
   {
      if( (infile = fopen(argv[1], "rb")) == NULL )
      {
         fprintf(stderr, "Error reading %s\n", argv[1]);
         return 1;
      }
      Decode(infile);
      (void)fclose(infile);
   }
   else
   {
      printf("%s [input.txt] > output.bin\n", *argv);
   }
   return 0;
}