/* backupfile.c -- make Emacs style backup file names
   Copyright (C) 1990 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */

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

#include <stdio.h>
#include <ctype.h>
#include <sys/types.h>
#include "backupfile.h"
#if defined(STDC_HEADERS) || defined(HAVE_STRING_H)
#include <string.h>
#ifndef index
#define index strchr
#endif
#ifndef rindex
#define rindex strrchr
#endif
#else
#include <strings.h>
#endif

#if defined(DIRENT) || defined(_POSIX_VERSION)
#include <dirent.h>
#define NLENGTH(direct) (strlen((direct)->d_name))
#else /* not (DIRENT or _POSIX_VERSION) */
#define dirent direct
#define NLENGTH(direct) ((direct)->d_namlen)
#ifdef SYSNDIR
#include <sys/ndir.h>
#endif /* SYSNDIR */
#ifdef SYSDIR
#include <sys/dir.h>
#endif /* SYSDIR */
#ifdef NDIR
#include <ndir.h>
#endif /* NDIR */
#endif /* DIRENT or _POSIX_VERSION */

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

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

#if !defined (isascii) || defined (STDC_HEADERS)
#undef isascii
#define isascii(c) 1
#endif

#define ISDIGIT(c) (isascii ((unsigned char ) c) \
		    && isdigit ((unsigned char) (c)))

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

#if defined (_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 = "~";

char *basename ();
char *dirname ();
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)
     char *file;
{
  char *dir;
  char *base_versions;
  int highest_backup;

  if (backup_type == simple)
    return concat (file, simple_backup_suffix);
  base_versions = concat (basename (file), ".~");
  if (base_versions == 0)
    return 0;
  dir = dirname (file);
  if (dir == 0)
    {
      free (base_versions);
      return 0;
    }
  highest_backup = max_backup_version (base_versions, dir);
  free (base_versions);
  free (dir);
  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)
     char *file, *dir;
{
  DIR *dirp;
  struct dirent *dp;
  int highest_version;
  int this_version;
  int 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)
     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)
     char *base;
     char *backup;
     int base_length;
{
  int version;
  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)
     char *str1, *str2;
{
  char *newstr;
  char 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;
}