/* $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>
#include <err.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

bool    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.
 *
 * Returns true if truncation was needed to do the replacement, false if
 * truncation was not required.
 */
bool
strnsubst(char **str, const char *match, const char *replstr, size_t maxsize)
{
        char *s1, *s2, *this;
        bool error = false;

        s1 = *str;
        if (s1 == NULL)
                return false;
        /*
         * If maxsize is 0 then set it 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(1, maxsize);
        if (s2 == NULL)
                err(1, "calloc");

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

        if (match == NULL || replstr == NULL || maxsize == strlen(s1)) {
                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) {
                        strlcat(s2, s1, maxsize);
                        error = true;
                        goto done;
                }
                strncat(s2, s1, (uintptr_t)this - (uintptr_t)s1);
                strcat(s2, replstr);
                s1 = this + strlen(match);
        }
        strcat(s2, s1);
done:
        *str = s2;
        return error;
}

#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)
                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