/* Copyright (C) 1991 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If
   not, write to the Free Software Foundation, Inc., 675 Mass Ave,
   Cambridge, MA 02139, USA.  */

#include <sys/types.h>
#include <errno.h>

#if defined (HAVE_LIMITS_H)
#  include <limits.h>
#endif

#if defined (HAVE_DIRENT_H)
#  include <dirent.h>
#else
#  include <sys/dir.h>
#  if !defined (dirent)
#    define dirent direct
#  endif /* !dirent */
#endif /* !HAVE_DIRENT_H */

#if defined (HAVE_UNISTD_H)
#  include <unistd.h>
#endif

#include "posixstat.h"
#include "maxpath.h"
#include "config.h"

#if defined (HAVE_STDLIB_H)
#  include <stdlib.h>
#else
#  include "ansi_stdlib.h"
#endif /* !HAVE_STDLIB_H */

#if defined (HAVE_STRING_H)
#  include <string.h>
#else
#  include <strings.h>
#endif /* !HAVE_STRING_H */

/* Not all systems declare ERRNO in errno.h... and some systems #define it! */
#if !defined (errno)
extern int errno;
#endif /* !errno */

#if defined (__STDC__)
#  define CONST const
#  define PTR void *
#else /* !__STDC__ */
#  define CONST
#  define PTR char *
#endif /* !__STDC__ */

#if !defined (PATH_MAX)
#  if defined (MAXPATHLEN)
#    define PATH_MAX MAXPATHLEN
#  else /* !MAXPATHLEN */
#    define PATH_MAX 1024
#  endif /* !MAXPATHLEN */
#endif /* !PATH_MAX */

#if defined (_POSIX_VERSION) || defined (USGr3) || defined (HAVE_DIRENT_H)
#  if !defined (HAVE_DIRENT)
#    define HAVE_DIRENT
#  endif /* !HAVE_DIRENT */
#endif /* _POSIX_VERSION || USGr3 || HAVE_DIRENT_H */

#if defined (HAVE_DIRENT)
#  define D_NAMLEN(d)	(strlen ((d)->d_name))
#else
#  define D_NAMLEN(d)	((d)->d_namlen)
#endif /* ! (_POSIX_VERSION || USGr3) */

#if defined (USG) || defined (USGr3)
#  define d_fileno d_ino
#endif

#if !defined (alloca)
extern char *alloca ();
#endif /* alloca */

/* Heuristic to tell whether or not the current machine has lstat(2).
   Can probably be fooled easily. */
#if !defined (S_ISLNK)
#  define lstat stat
#endif

/* Get the pathname of the current working directory,
   and put it in SIZE bytes of BUF.  Returns NULL if the
   directory couldn't be determined or SIZE was too small.
   If successful, returns BUF.  In GNU, if BUF is NULL,
   an array is allocated with `malloc'; the array is SIZE
   bytes long, unless SIZE <= 0, in which case it is as
   big as necessary.  */
#if defined (__STDC__)
char *
getcwd (char *buf, int size)
#else /* !__STDC__ */
char *
getcwd (buf, size)
     char *buf;
     size_t size;
#endif /* !__STDC__ */
{
  static CONST char dots[]
    = "../../../../../../../../../../../../../../../../../../../../../../../\
../../../../../../../../../../../../../../../../../../../../../../../../../../\
../../../../../../../../../../../../../../../../../../../../../../../../../..";
  CONST char *dotp, *dotlist;
  size_t dotsize;
  dev_t rootdev, thisdev;
  ino_t rootino, thisino;
  char path[PATH_MAX + 1];
  register char *pathp;
  char *pathbuf;
  size_t pathsize;
  struct stat st;

  if (buf != NULL && size == 0)
    {
      errno = EINVAL;
      return ((char *)NULL);
    }

  pathsize = sizeof (path);
  pathp = &path[pathsize];
  *--pathp = '\0';
  pathbuf = path;

  if (stat (".", &st) < 0)
    return ((char *)NULL);
  thisdev = st.st_dev;
  thisino = st.st_ino;

  if (stat ("/", &st) < 0)
    return ((char *)NULL);
  rootdev = st.st_dev;
  rootino = st.st_ino;

  dotsize = sizeof (dots) - 1;
  dotp = &dots[sizeof (dots)];
  dotlist = dots;
  while (!(thisdev == rootdev && thisino == rootino))
    {
      register DIR *dirstream;
      register struct dirent *d;
      dev_t dotdev;
      ino_t dotino;
      char mount_point;
      int namlen;

      /* Look at the parent directory.  */
      if (dotp == dotlist)
	{
	  /* My, what a deep directory tree you have, Grandma.  */
	  char *new;
	  if (dotlist == dots)
	    {
	      new = malloc (dotsize * 2 + 1);
	      if (new == NULL)
		goto lose;
	      memcpy (new, dots, dotsize);
	    }
	  else
	    {
	      new = realloc ((PTR) dotlist, dotsize * 2 + 1);
	      if (new == NULL)
		goto lose;
	    }
	  memcpy (&new[dotsize], new, dotsize);
	  dotp = &new[dotsize];
	  dotsize *= 2;
	  new[dotsize] = '\0';
	  dotlist = new;
	}

      dotp -= 3;

      /* Figure out if this directory is a mount point.  */
      if (stat (dotp, &st) < 0)
	goto lose;
      dotdev = st.st_dev;
      dotino = st.st_ino;
      mount_point = dotdev != thisdev;

      /* Search for the last directory.  */
      dirstream = opendir (dotp);
      if (dirstream == NULL)
	goto lose;
      while ((d = readdir (dirstream)) != NULL)
	{
	  if (d->d_name[0] == '.' &&
	      (d->d_name[1] == '\0' ||
		(d->d_name[1] == '.' && d->d_name[2] == '\0')))
	    continue;
	  if (mount_point || d->d_fileno == thisino)
	    {
	      char *name;

	      namlen = D_NAMLEN(d);
	      name = (char *)
		alloca (dotlist + dotsize - dotp + 1 + namlen + 1);
	      memcpy (name, dotp, dotlist + dotsize - dotp);
	      name[dotlist + dotsize - dotp] = '/';
	      memcpy (&name[dotlist + dotsize - dotp + 1],
		      d->d_name, namlen + 1);
	      if (lstat (name, &st) < 0)
		{
		  int save = errno;
		  (void) closedir (dirstream);
		  errno = save;
		  goto lose;
		}
	      if (st.st_dev == thisdev && st.st_ino == thisino)
		break;
	    }
	}
      if (d == NULL)
	{
	  int save = errno;
	  (void) closedir (dirstream);
	  errno = save;
	  goto lose;
	}
      else
	{
	  size_t space;

	  while ((space = pathp - pathbuf) <= namlen)
	    {
	      char *new;

	      if (pathbuf == path)
		{
		  new = malloc (pathsize * 2);
		  if (!new)
		    goto lose;
		}
	      else
		{
		  new = realloc ((PTR) pathbuf, (pathsize * 2));
		  if (!new)
		    goto lose;
		  pathp = new + space;
		}
	      (void) memcpy (new + pathsize + space, pathp, pathsize - space);
	      pathp = new + pathsize + space;
	      pathbuf = new;
	      pathsize *= 2;
	    }

	  pathp -= namlen;
	  (void) memcpy (pathp, d->d_name, namlen);
	  *--pathp = '/';
	  (void) closedir (dirstream);
	}

      thisdev = dotdev;
      thisino = dotino;
    }

  if (pathp == &path[sizeof(path) - 1])
    *--pathp = '/';

  if (dotlist != dots)
    free ((PTR) dotlist);

  {
    size_t len = pathbuf + pathsize - pathp;
    if (buf == NULL)
      {
	if (len < (size_t) size)
	  len = size;
	buf = (char *) malloc (len);
	if (buf == NULL)
	  goto lose2;
      }
    else if ((size_t) size < len)
      {
	errno = ERANGE;
	goto lose2;
      }
    (void) memcpy((PTR) buf, (PTR) pathp, len);
  }

  if (pathbuf != path)
    free (pathbuf);

  return (buf);

 lose:
  if ((dotlist != dots) && dotlist)
    {
      int e = errno;
      free ((PTR) dotlist);
      errno = e;
    }

 lose2:
  if ((pathbuf != path) && pathbuf)
    {
      int e = errno;
      free ((PTR) pathbuf);
      errno = e;
    }
  return ((char *)NULL);
}

#if defined (TEST)
#  include <stdio.h>
main (argc, argv)
     int argc;
     char **argv;
{
  char b[PATH_MAX];

  if (getcwd(b, sizeof(b)))
    {
      printf ("%s\n", b);
      exit (0);
    }
  else
    {
      perror ("cwd: getcwd");
      exit (1);
    }
}
#endif /* TEST */