/*
 * regsub
 *
 *	Copyright (c) 1986 by University of Toronto.
 *	Written by Henry Spencer.  Not derived from licensed software.
 *
 *	Permission is granted to anyone to use this software for any
 *	purpose on any computer system, and to redistribute it freely,
 *	subject to the following restrictions:
 *
 *	1. The author is not responsible for the consequences of use of
 *		this software, no matter how awful, even if they arise
 *		from defects in it.
 *
 *	2. The origin of this software must not be misrepresented, either
 *		by explicit claim or by omission.
 *
 *	3. Altered versions must be plainly marked as such, and must not
 *		be misrepresented as being the original software.
 */

#include "libutil.h"
#include "regmagic.h"


#ifndef CHARBITS
#define	UCHARAT(p)	((int)*(unsigned char *)(p))
#else
#define	UCHARAT(p)	((int)*(p)&CHARBITS)
#endif

/*
 - regsub - perform substitutions after a regexp match
 */
void
regsub (const regexp * prog, const char *source, char *dest)
{
  register char *src;
  register char *dst;
  register char c;
  register int no;
  register int len;

  if (prog == NULL || source == NULL || dest == NULL)
    {
      regerror ("NULL parm to regsub");
      return;
    }
  if (UCHARAT (prog->program) != MAGIC)
    {
      regerror ("damaged regexp fed to regsub");
      return;
    }

  src = (char *) source;
  dst = dest;
  while ((c = *src++) != '\0')
    {
      if (c == '&')
	no = 0;
      else if (c == '\\' && '0' <= *src && *src <= '9')
	no = *src++ - '0';
      else
	no = -1;
      if (no < 0)
	{			/* Ordinary character. */
	  if (c == '\\' && (*src == '\\' || *src == '&'))
	    c = *src++;
	  *dst++ = c;
	}
      else if (prog->startp[no] != NULL && prog->endp[no] != NULL)
	{
	  len = (int) (prog->endp[no] - prog->startp[no]);
	  (void) strncpy (dst, prog->startp[no], len);
	  dst += len;
	  if (len != 0 && *(dst - 1) == '\0')
	    {			/* strncpy hit NUL. */
	      regerror ("damaged match string");
	      return;
	    }
	}
    }
  *dst++ = '\0';
}
