/* $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
