/*      $OpenBSD: strnsubst.c,v 1.8 2023/04/19 12:58:16 jsg Exp $       */
/*      $FreeBSD: strnsubst.c,v 1.6 2002/06/22 12:58:42 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 <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.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;
        size_t matchlen, s2len;
        int n;

        if ((s1 = *str) == NULL)
                return;
        if ((s2 = malloc(maxsize)) == NULL)
                err(1, NULL);

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

        if (match == NULL || *match == '\0' || strlen(s1) >= maxsize) {
                strlcpy(s2, s1, maxsize);
                goto done;
        }

        *s2 = '\0';
        s2len = 0;
        matchlen = strlen(match);
        for (;;) {
                if ((this = strstr(s1, match)) == NULL)
                        break;
                n = snprintf(s2 + s2len, maxsize - s2len, "%.*s%s",
                    (int)(this - s1), s1, replstr);
                if (n < 0 || n + s2len + strlen(this + matchlen) >= maxsize)
                        break;                  /* out of room */
                s2len += n;
                s1 = this + matchlen;
        }
        strlcpy(s2 + s2len, s1, maxsize - s2len);
done:
        *str = s2;
        return;
}

#ifdef TEST

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)
                printf("strnsubst() seems to work!\n");
        else
                printf("strnsubst() is broken.\n");
        printf("%s\n", z);
        free(x);
        free(y);
        free(z);
        free(za);
        return 0;
}
#endif