/*
 * quoted-printable [-e|-E|-d]
 *
 * -e specifies encoding, -d decoding.  -E specifies encoding like -e,
 *  but it encodes more characters, including several that may be
 *  problematic if the message passes through an EBCDIC machine, and
 *  minus signs at the beginnings of lines.  Note that when encoding,
 *  if the input is lacking a final trailing newline, the output will
 *  end with a quoted-printable soft line break with nothing following
 *  it, so as to ensure that the output always ends with a newline.
 */

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

extern const char *__progname;

static char xdig[] = "0123456789ABCDEF";
static char paranoid_danger[] = "\t!\"#$@[\\]^`{|}~";

static void encode(int paranoid)
{
 int c;
 int olen;
 int lbeg;
 int ws;

 olen = 0;
 lbeg = 1;
 ws = 0;
 while (1)
  { c = getchar();
    if (c == EOF) break;
    if (olen > 70)
     { printf("=\n");
       olen = 0;
       lbeg = 1;
       ws = 0;
     }
    if (c == '\n')
     { if (ws) printf("=\n");
       putchar('\n');
       olen = 0;
       lbeg = 1;
       ws = 0;
     }
    else if ((c == ' ') || (c == '\t'))
     { putchar(c);
       olen ++;
       lbeg = 0;
       ws = 1;
     }
    else if ( (c < 32) || (c > 126) || (c == '=') ||
	      ( paranoid &&
    		( (lbeg && (c == '-')) ||
		  index(paranoid_danger,c) ) ) )
     { if (c & ~0xff)
	{ fprintf(stderr,"%s: out-of-range input character 0x%x dropped\n",__progname,c);
	}
       else
	{ putchar('=');
	  putchar(xdig[(c>>4)&15]);
	  putchar(xdig[c&15]);
	  olen += 3;
	  lbeg = 0;
	  ws = 0;
	}
     }
    else
     { putchar(c);
       olen ++;
       lbeg = 0;
       ws = 0;
     }
  }
 if (olen > 0) printf("=\n");
}

static void decode(void)
{
 int ilen;
 char *xp;
 int xbuf;
 enum { EQS_NONE = 1, EQS_EQUAL, EQS_MIDHEX } eqstate;
 int c;
 unsigned char *spcbuf;
 int spchave;
 int spclen;
 int spcptr;

 spcbuf = malloc(1);
 spchave = 0;
 spclen = 0;
 spcptr = 0;
 ilen = 0;
 eqstate = EQS_NONE;
 while (1)
  { if (spcptr > 0)
     { c = spcbuf[spcptr++];
       if (spcptr >= spclen)
	{ spcptr = 0;
	  spclen = 0;
	}
     }
    else
     { c = getchar();
       if (c == EOF) break;
       switch (c)
	{ case ' ': case '\t':
	     while (spclen >= spchave) spcbuf = realloc(spcbuf,(spchave+=8)+1);
	     spcbuf[spclen++] = c;
	     continue;
	     break;
	  case '\n':
	     spclen = 0;
	     break;
	}
       if (spclen > 0)
	{ spcbuf[spclen++] = c;
	  spcptr = 1;
	  c = spcbuf[0];
	}
     }
    if (c == '\n')
     { ilen = 0;
     }
    else
     { if (ilen++ == 76)
	{ fprintf(stderr,"%s: warning: input line exceeds standard maximum length\n",__progname);
	}
     }
    switch (eqstate)
     { case EQS_NONE:
	  if (c == '=')
	   { eqstate = EQS_EQUAL;
	   }
	  else
	   { putchar(c);
	   }
	  break;
       case EQS_EQUAL:
	  if (c == '\n')
	   { eqstate = EQS_NONE;
	   }
	  else
	   { xp = index(xdig,c);
	     if (xp)
	      { eqstate = EQS_MIDHEX;
		xbuf = (xp-xdig) << 4;
	      }
	     else
	      { fprintf(stderr,"%s: invalid character 0x%x after =\n",__progname,(unsigned int)c);
		eqstate = EQS_NONE;
	      }
	   }
	  break;
       case EQS_MIDHEX:
	  eqstate = EQS_NONE;
	  xp = index(xdig,c);
	  if (xp)
	   { putchar(xbuf|(xp-xdig));
	   }
	  else
	   { fprintf(stderr,"%s: invalid second character 0x%x in hex = encoding\n",__progname,(unsigned int)c);
	   }
	  break;
     }
  }
 free(spcbuf);
}

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