/* $xMach: strnsubst.c,v 1.3 2002/02/23 02:10:24 jmallett Exp $ */

/*
* Copyright (c) 2002 J. Mallett.  All rights reserved.
* You may do whatever you want with this file as long as
* the above copyright and this notice remain intact, along
* with the following statement:
*      For the man who taught me vi, and who got too old, too young.
*/

#include <sys/cdefs.h>
#ifndef lint
#if 0
__FBSDID("$FreeBSD: src/usr.bin/xargs/strnsubst.c,v 1.8 2005/12/30 23:22:50 jmallett Exp $");
#endif
__RCSID("$NetBSD: strnsubst.c,v 1.1 2007/04/18 15:56:07 christos Exp $");
#endif /* not lint */

#include <err.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdint.h>

void    strnsubst(char **, const char *, const char *, size_t);

/*
* Replaces str with a string consisting of str with match replaced with
* replstr as many times as can be done before the constructed string is
* maxsize bytes large.  It does not free the string pointed to by str, it
* is up to the calling program to be sure that the original contents of
* str as well as the new contents are handled in an appropriate manner.
* If replstr is NULL, then that internally is changed to a nil-string, so
* that we can still pretend to do somewhat meaningful substitution.
* No value is returned.
*/
void
strnsubst(char **str, const char *match, const char *replstr, size_t maxsize)
{
       char *s1, *s2, *this;

       s1 = *str;
       if (s1 == NULL)
               return;
       /*
        * If maxsize is 0 then set it to to the length of s1, because we have
        * to duplicate s1.  XXX we maybe should double-check whether the match
        * appears in s1.  If it doesn't, then we also have to set the length
        * to the length of s1, to avoid modifying the argument.  It may make
        * sense to check if maxsize is <= strlen(s1), because in that case we
        * want to return the unmodified string, too.
        */
       if (maxsize == 0) {
               match = NULL;
               maxsize = strlen(s1) + 1;
       }
       s2 = calloc(maxsize, 1);
       if (s2 == NULL)
               err(1, "calloc");

       if (replstr == NULL)
               replstr = "";

       if (match == NULL || replstr == NULL || maxsize == strlen(s1)) {
               (void)strlcpy(s2, s1, maxsize);
               goto done;
       }

       for (;;) {
               this = strstr(s1, match);
               if (this == NULL)
                       break;
               if ((strlen(s2) + strlen(s1) + strlen(replstr) -
                   strlen(match) + 1) > maxsize) {
                       (void)strlcat(s2, s1, maxsize);
                       goto done;
               }
               (void)strncat(s2, s1, (uintptr_t)this - (uintptr_t)s1);
               (void)strcat(s2, replstr);
               s1 = this + strlen(match);
       }
       (void)strcat(s2, s1);
done:
       *str = s2;
       return;
}

#ifdef TEST
#include <stdio.h>

int
main(void)
{
       char *x, *y, *z, *za;

       x = "{}%$";
       strnsubst(&x, "%$", "{} enpury!", 255);
       y = x;
       strnsubst(&y, "}{}", "ybir", 255);
       z = y;
       strnsubst(&z, "{", "v ", 255);
       za = z;
       strnsubst(&z, NULL, za, 255);
       if (strcmp(z, "v ybir enpury!") == 0)
               (void)printf("strnsubst() seems to work!\n");
       else
               (void)printf("strnsubst() is broken.\n");
       (void)printf("%s\n", z);
       free(x);
       free(y);
       free(z);
       free(za);
       return 0;
}
#endif