/*
 * Copyright (c) 1989, 1991 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)getcwd.c	5.11 (Berkeley) 2/24/91";
#endif /* LIBC_SCCS and not lint */

#include <sys/stat.h>
#include <errno.h>
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/syslimits.h>
#include <reent.h>
#include <_syslist.h>

#define bcopy(a, b, c) memmove(b, a, c)

#define ISDOT(dp)              \
    (dp->d_name[0] == '.' &&   \
     (dp->d_name[1] == '\0' || \
      (dp->d_name[1] == '.' && dp->d_name[2] == '\0')))

char* getcwd(pt, size) char* pt;
size_t size;
{
    register struct dirent* dp;
    register DIR* dir;
    register dev_t dev;
    register ino_t ino;
    register int first;
    register char *bpt, *bup;
    struct stat s;
    dev_t root_dev;
    ino_t root_ino;
    size_t ptsize, upsize;
    int save_errno;
    char *ept, *eup, *up;

    /*
     * If no buffer specified by the user, allocate one as necessary.
     * If a buffer is specified, the size has to be non-zero.  The path
     * is built from the end of the buffer backwards.
     */

    if (pt) {
        ptsize = 0;
        if (!size) {
            errno = EINVAL;
            return (char*)NULL;
        }
        ept = pt + size;
    } else {
        if (!(pt = (char*)malloc(ptsize = 1024 - 4))) {
            return (char*)NULL;
        }
        ept = pt + ptsize;
    }
    bpt = ept - 1;
    *bpt = '\0';

    /*
     * Allocate bytes (1024 - malloc space) for the string of "../"'s.
     * Should always be enough (it's 340 levels).  If it's not, allocate
     * as necessary.  Special * case the first stat, it's ".", not "..".
     */

    if (!(up = (char*)malloc(upsize = 1024 - 4))) {
        goto err;
    }
    eup = up + MAXNAMLEN;
    bup = up;
    up[0] = '.';
    up[1] = '\0';

    /* Save root values, so know when to stop. */
    if (stat("/", &s)) goto err;
    root_dev = s.st_dev;
    root_ino = s.st_ino;

    errno = 0; /* XXX readdir has no error return. */

    for (first = 1;; first = 0) {
        /* Stat the current level. */
        if (stat(up, &s)) goto err;

        /* Save current node values. */
        ino = s.st_ino;
        dev = s.st_dev;

        /* Check for reaching root. */
        if (root_dev == dev && root_ino == ino) {
            *--bpt = '/';
            /*
             * It's unclear that it's a requirement to copy the
             * path to the beginning of the buffer, but it's always
             * been that way and stuff would probably break.
             */
            (void)bcopy(bpt, pt, ept - bpt);
            free(up);
            return pt;
        }

        /*
         * Build pointer to the parent directory, allocating memory
         * as necessary.  Max length is 3 for "../", the largest
         * possible component name, plus a trailing NULL.
         */

        if (bup + 3 + MAXNAMLEN + 1 >= eup) {
            if (!(up = (char*)realloc(up, upsize *= 2))) {
                goto err;
            }
            bup = up;
            eup = up + upsize;
        }
        *bup++ = '.';
        *bup++ = '.';
        *bup = '\0';

        /* Open and stat parent directory. */
        if (!(dir = opendir(up)) || fstat(dirfd(dir), &s)) goto err;

        /* Add trailing slash for next directory. */
        *bup++ = '/';

        /*
         * If it's a mount point, have to stat each element because
         * the inode number in the directory is for the entry in the
         * parent directory, not the inode number of the mounted file.
         */

        save_errno = 0;
        if (s.st_dev == dev) {
            for (;;) {
                if (!(dp = readdir(dir))) goto notfound;
                if (dp->d_ino == ino) break;
            }
        } else
            for (;;) {
                if (!(dp = readdir(dir))) goto notfound;
                if (ISDOT(dp)) continue;
                bcopy(dp->d_name, bup, strlen(dp->d_name) + 1);

                /* Save the first error for later. */
                if (stat(up, &s)) {
                    if (!save_errno) save_errno = errno;
                    errno = 0;
                    continue;
                }
                if (s.st_dev == dev && s.st_ino == ino) break;
            }

        /*
         * Check for length of the current name, preceding slash,
         * leading slash.
         */

        if (bpt - pt <= strlen(dp->d_name) + (first ? 1 : 2)) {
            size_t len, off;

            if (!ptsize) {
                errno = ERANGE;
                goto err;
            }
            off = bpt - pt;
            len = ept - bpt;
            if (!(pt = (char*)realloc(pt, ptsize *= 2))) {
                goto err;
            }
            bpt = pt + off;
            ept = pt + ptsize;
            (void)bcopy(bpt, ept - len, len);
            bpt = ept - len;
        }
        if (!first) *--bpt = '/';
        bpt -= strlen(dp->d_name);
        bcopy(dp->d_name, bpt, strlen(dp->d_name));
        (void)closedir(dir);

        /* Truncate any file name. */
        *bup = '\0';
    }

notfound:
    /*
     * If readdir set errno, use it, not any saved error; otherwise,
     * didn't find the current directory in its parent directory, set
     * errno to ENOENT.
     */

    if (!errno) errno = save_errno ? save_errno : ENOENT;
    /* FALLTHROUGH */

err:
    if (ptsize) free(pt);
    free(up);
    return (char*)NULL;
}

char* getwd(char* buf) { return getcwd(buf, PATH_MAX); }

char* get_current_dir_name(void)
{
    struct stat sbuf1, sbuf2;
    char* pwd = getenv("PWD");
    char* cwd = getcwd(NULL, 0);
    int retval;

    if (pwd) {
        retval = stat(pwd, &sbuf1);
        if (retval < 0) goto err;
        retval = stat(cwd, &sbuf2);
        if (retval < 0) goto err;

        if (sbuf1.st_dev == sbuf2.st_dev && sbuf1.st_ino == sbuf2.st_ino) {
            free(cwd);
            cwd = strdup(pwd);
        }
    }

    return cwd;

err:
    free(cwd);
    return NULL;
}
