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

   11/30/01
                                                                           */

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


static /*@null@*/char **LoadImage(FILE *infile, int width, int height);
static char DownSample(char a, char b, char c, char d);

/******************************************************************** main */
int main(int argc, char **argv)
{
   FILE *infile, *outfile;
   int width, height, x, y;
   char **src;

   if( argc < 5 )
      return printf("%s <width> <height> <in> <out>\n", *argv);
   width = atoi(argv[1]);
   height = atoi(argv[2]);
   if( width < 2 || height < 2 || (width & 1) != 0 || (height & 1) != 0 )
      return printf("Invalid input size: %d x %d\n", width, height);

   if( (infile = fopen(argv[3], "rt")) == NULL )
      return printf("Can not open %s\n", argv[3]);
   if( (outfile = fopen(argv[4], "wt+")) == NULL )
   {
      (void)fclose(infile);
      return printf("Can not create %s\n", argv[4]);
   }


   if( (src = LoadImage(infile, width, height)) == NULL )
   {
      (void)fclose(infile);
      (void)fclose(outfile);
      return 1;
   }


   for(y = 0; y < height; y += 2)
   {
      for(x = 0; x < width; x += 2)
      {
         (void)fputc(DownSample(src[y  ][x], src[y  ][x+1],
                                src[y+1][x], src[y+1][x+1]), outfile);
      }
      (void)fputc('\n', outfile);
   }


   (void)fclose(infile);
   (void)fclose(outfile);
   for(y = 0; y < height; free(src[y++]));
   free(src);
   return 0;

} /* main() */

/************************************************************** DownSample */
static char DownSample(char a, char b, char c, char d)
{
   unsigned int block;

   block = (((unsigned int)a) << 24) |
           (((unsigned int)b) << 16) |
           (((unsigned int)c) << 8) |
           ((unsigned int)d);
   switch( block )
   {
      case 0x58585858:  return '%';
      case 0x58585820:
      case 0x58582058:
      case 0x58205858:
      case 0x20585858:  return 'X';
      case 0x58582020:  return '\"';
      case 0x58202058:
      case 0x20585820:
      case 0x20205858:  return 'x';
      case 0x58205820:
      case 0x20582058:  return ':';
      case 0x58202020:  return '\'';
      case 0x20582020:  return '`';
      case 0x20205820:  return '.';
      case 0x20202058:  return ',';
      default:
         break;
   }
   return ' ';

} /* DownSample() */

/*************************************************************** LoadImage */
static char **LoadImage(FILE *infile, int width, int height)
{
   char **image;
   int i, j;

   if( (image = (char**)malloc(height * sizeof(char*))) == NULL )
   {
      (void)puts("Not enough memory\n");
      return NULL;
   }

   for(i = 0; i < height; i++)
   {
      if( (image[i] = (char*)malloc((size_t)(width + 2))) == NULL )
      {
         for(j = 0; j <= i; free(image[j++]));
         free(image);
         (void)puts("Not enough memory\n");
         return NULL;
      }

      memset(image[i], 32, (size_t)width);
      if( fgets(image[i], width + 2, infile) == NULL )
      {
         for(j = 0; j <= i; free(image[j++]));
         free(image);
         (void)puts("Read error\n");
         return NULL;
      }
   }

   return image;

} /* LoadImage() */