/*
 * urlenc -d
 *
 * -d specifies decoding; someday, other operations (such as encoding)
 *  may be supported.
 *
 * This file is in the public domain.
 */

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

extern const char *__progname;

static int hexval(char c)
{
 switch (c)
  { case '0': return(0); break;
    case '1': return(1); break;
    case '2': return(2); break;
    case '3': return(3); break;
    case '4': return(4); break;
    case '5': return(5); break;
    case '6': return(6); break;
    case '7': return(7); break;
    case '8': return(8); break;
    case '9': return(9); break;
    case 'A': return(10); break;
    case 'B': return(11); break;
    case 'C': return(12); break;
    case 'D': return(13); break;
    case 'E': return(14); break;
    case 'F': return(15); break;
    case 'a':
       fprintf(stderr,"%s: lowercase hex digit in %% escape\n",__progname);
       return(10);
       break;
    case 'b':
       fprintf(stderr,"%s: lowercase hex digit in %% escape\n",__progname);
       return(11);
       break;
    case 'c':
       fprintf(stderr,"%s: lowercase hex digit in %% escape\n",__progname);
       return(12);
       break;
    case 'd':
       fprintf(stderr,"%s: lowercase hex digit in %% escape\n",__progname);
       return(13);
       break;
    case 'e':
       fprintf(stderr,"%s: lowercase hex digit in %% escape\n",__progname);
       return(14);
       break;
    case 'f':
       fprintf(stderr,"%s: lowercase hex digit in %% escape\n",__progname);
       return(15);
       break;
  }
 fprintf(stderr,"%s: bad hex digit in %% escape (ignoring)\n",__progname);
 return(-1);
}

static void decode(void)
{
 int c;
 int v;
 int h;

 while (1)
  { c = getchar();
    if (c == EOF) break;
    if (c != '%')
     { putchar(c);
       continue;
     }
    c = getchar();
    if (c == EOF)
     { fprintf(stderr,"%s: EOF within %% escape\n",__progname);
       break;
     }
    h = hexval(c);
    if (h < 0) continue;
    v = h;
    c = getchar();
    if (c == EOF)
     { fprintf(stderr,"%s: EOF within %% escape\n",__progname);
       break;
     }
    h = hexval(c);
    if (h < 0) continue;
    v = (v << 4) + h;
    putchar(v);
  }
}

int main(int, char **);
int main(int ac, char **av)
{
 if (0)
  {
usage:;
    fprintf(stderr,"Usage: %s -d\n",__progname);
    exit(1);
  }
 if (ac != 2) goto usage;
      if (!strcmp(av[1],"-d")) decode();
 else goto usage;
 exit(0);
}