/* backupfile.c -- make Emacs style backup file names
   Copyright (C) 1990, 1997 Free Software Foundation, Inc.

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

   This program 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 General
   Public License for more details.

   You should have received a copy of the GNU General Public License along
   with this program; if not, write to the Free Software Foundation, Inc.,
   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* David MacKenzie <djm@gnu.ai.mit.edu>.
   Some algorithms adapted from GNU Emacs.  */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <stdio.h>
#include <ctype.h>
#include <sys/types.h>
#include "backupfile.h"

#if HAVE_STRING_H
# include <string.h>
#else
# include <strings.h>
# ifndef strrchr
#  define strrchr rindex
# endif
#endif

#if HAVE_DIRENT_H
# include <dirent.h>
# define NLENGTH(Direct) (strlen((Direct)->d_name))
#else
# define dirent direct
# define NLENGTH(Direct) ((Direct)->d_namlen)
# if HAVE_SYS_NDIR_H
#  include <sys/ndir.h>
# endif
# if HAVE_SYS_DIR_H
#  include <sys/dir.h>
# endif
# if HAVE_NDIR_H
#  include <ndir.h>
# endif
#endif

#if CLOSEDIR_VOID
/* Fake a return value.  */
# define CLOSEDIR(d) (closedir (d), 0)
#else
# define CLOSEDIR(d) closedir (d)
#endif

#if STDC_HEADERS
# include <stdlib.h>
#else
char *malloc ();
#endif

#if defined (STDC_HEADERS) || (!defined (isascii) && !defined (HAVE_ISASCII))
# define IN_CTYPE_DOMAIN(Char) 1
#else
# define IN_CTYPE_DOMAIN(Char) isascii(Char)
#endif

#define ISDIGIT(Char) (IN_CTYPE_DOMAIN ((unsigned char) (Char)) \
		       && isdigit ((unsigned char) (Char)))

#if HAVE_UNISTD_H
# include <unistd.h>
#endif

#ifdef _POSIX_VERSION
/* POSIX does not require that the d_ino field be present, and some
   systems do not provide it.  */
# define REAL_DIR_ENTRY(Dp) 1
#else
# define REAL_DIR_ENTRY(Dp) ((Dp)->d_ino != 0)
#endif

/* Which type of backup file names are generated.  */
enum backup_type backup_type = none;

/* The extension added to file names to produce a simple (as opposed
   to numbered) backup file name.  */
char *simple_backup_suffix = "~";

static char *concat ();
char *find_backup_file_name ();
static char *make_version_name ();
static int max_backup_version ();
static int version_number ();

/* Return the name of the new backup file for file FILE,
   allocated with malloc.  Return 0 if out of memory.
   FILE must not end with a '/' unless it is the root directory.
   Do not call this function if backup_type == none.  */

char *
find_backup_file_name (file)
     const char *file;
{
  char *copy;
  char *base;
  const char *dir;
  char *base_versions;
  int highest_backup;

  if (backup_type == simple)
    return concat (file, simple_backup_suffix);

  copy = malloc (strlen (file) + 1);
  if (copy == 0)
    return 0;
  strcpy (copy, file);

  base = strrchr (copy, '/');
  if (base == 0)
    {
      base = copy;
      dir = ".";
    }
  else
    {
      *base++ = '\0';
      dir = copy;
    }

  base_versions = concat (base, ".~");
  if (base_versions == 0)
    {
      free (copy);
      return 0;
    }

  highest_backup = max_backup_version (base_versions, dir);
  free (copy);
  free (base_versions);

  if (backup_type == numbered_existing && highest_backup == 0)
    return concat (file, simple_backup_suffix);

  return make_version_name (file, highest_backup + 1);
}

/* Return the number of the highest-numbered backup file for file
   FILE in directory DIR.  If there are no numbered backups
   of FILE in DIR, or an error occurs reading DIR, return 0.
   FILE should already have ".~" appended to it.  */

static int
max_backup_version (file, dir)
     const char *file;
     const char *dir;
{
  DIR *dirp;
  struct dirent *dp;
  int highest_version;
  int this_version;
  size_t file_name_length;

  dirp = opendir (dir);
  if (!dirp)
    return 0;

  highest_version = 0;
  file_name_length = strlen (file);

  while ((dp = readdir (dirp)) != 0)
    {
      if (!REAL_DIR_ENTRY (dp) || NLENGTH (dp) <= file_name_length)
	continue;

      this_version = version_number (file, dp->d_name, file_name_length);
      if (this_version > highest_version)
	highest_version = this_version;
    }
  if (CLOSEDIR (dirp))
    return 0;
  return highest_version;
}

/* Return a string, allocated with malloc, containing
   "FILE.~VERSION~".  Return 0 if out of memory.  */

static char *
make_version_name (file, version)
     const char *file;
     int version;
{
  char *backup_name;

  backup_name = malloc (strlen (file) + 16);
  if (backup_name == 0)
    return 0;
  sprintf (backup_name, "%s.~%d~", file, version);
  return backup_name;
}

/* If BACKUP is a numbered backup of BASE, return its version number;
   otherwise return 0.  BASE_LENGTH is the length of BASE.
   BASE should already have ".~" appended to it.  */

static int
version_number (base, backup, base_length)
     const char *base;
     const char *backup;
     int base_length;
{
  int version;
  const char *p;

  version = 0;
  if (!strncmp (base, backup, base_length) && ISDIGIT (backup[base_length]))
    {
      for (p = &backup[base_length]; ISDIGIT (*p); ++p)
	version = version * 10 + *p - '0';
      if (p[0] != '~' || p[1])
	version = 0;
    }
  return version;
}

/* Return the newly-allocated concatenation of STR1 and STR2.
   If out of memory, return 0.  */

static char *
concat (str1, str2)
     const char *str1;
     const char *str2;
{
  char *newstr;
  int str1_length = strlen (str1);

  newstr = malloc (str1_length + strlen (str2) + 1);
  if (newstr == 0)
    return 0;
  strcpy (newstr, str1);
  strcpy (newstr + str1_length, str2);
  return newstr;
}