/* $OpenBSD: regsub.c,v 1.8 2026/04/04 11:32:05 nicm Exp $ */

/*
 * Copyright (c) 2019 Nicholas Marriott <nicholas.marriott@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>

#include <regex.h>
#include <string.h>

#include "tmux.h"

static void
regsub_copy(char **buf, ssize_t *len, const char *text, size_t start, size_t end)
{
        size_t  add = end - start;

        *buf = xrealloc(*buf, (*len) + add + 1);
        memcpy((*buf) + *len, text + start, add);
        (*len) += add;
}

static void
regsub_expand(char **buf, ssize_t *len, const char *with, const char *text,
    regmatch_t *m, u_int n)
{
        const char      *cp;
        u_int            i;

        for (cp = with; *cp != '\0'; cp++) {
                if (cp[0] == '\\' && cp[1] != '\0') {
                        cp++;
                        if (*cp >= '0' && *cp <= '9') {
                                i = *cp - '0';
                                if (i < n && m[i].rm_so != m[i].rm_eo) {
                                        regsub_copy(buf, len, text, m[i].rm_so,
                                            m[i].rm_eo);
                                        continue;
                                }
                        }
                }
                *buf = xrealloc(*buf, (*len) + 2);
                (*buf)[(*len)++] = *cp;
        }
}

char *
regsub(const char *pattern, const char *with, const char *text, int flags)
{
        regex_t          r;
        regmatch_t       m[10];
        ssize_t          start, end, last, len = 0;
        int              empty = 0;
        char            *buf = NULL;

        if (*text == '\0')
                return (xstrdup(""));
        if (*pattern == '\0')
                return (xstrdup(text));
        if (regcomp(&r, pattern, flags) != 0)
                return (NULL);

        start = 0;
        last = 0;
        end = strlen(text);

        while (start <= end) {
                if (regexec(&r, text + start, nitems(m), m, 0) != 0) {
                        regsub_copy(&buf, &len, text, start, end);
                        break;
                }

                /*
                 * Append any text not part of this match (from the end of the
                 * last match).
                 */
                regsub_copy(&buf, &len, text, last, m[0].rm_so + start);

                /*
                 * If the last match was empty and this one isn't (it is either
                 * later or has matched text), expand this match. If it is
                 * empty, move on one character and try again from there.
                 */
                if (empty ||
                    start + m[0].rm_so != last ||
                    m[0].rm_so != m[0].rm_eo) {
                        regsub_expand(&buf, &len, with, text + start, m,
                            nitems(m));

                        last = start + m[0].rm_eo;
                        start += m[0].rm_eo;
                        empty = 0;
                } else {
                        last = start + m[0].rm_eo;
                        start += m[0].rm_eo + 1;
                        empty = 1;
                }

                /* Stop now if anchored to start. */
                if (*pattern == '^') {
                        regsub_copy(&buf, &len, text, start, end);
                        break;
                }
        }
        buf[len] = '\0';

        regfree(&r);
        return (buf);
}