/* backupfile.c -- make Emacs style backup file names
   Copyright (C) 1990-1999, 2000-2003, 2005-2006 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; see the file COPYING.
   If not, write to the Free Software Foundation,
   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

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

#include <config.h>

#include "argmatch.h"
#include "backupfile.h"

#include <stdio.h>
#include <sys/types.h>
#if HAVE_STRING_H
# include <string.h>
#else
# include <strings.h>
#endif

#if HAVE_DIRENT_H
# include <dirent.h>
#endif

#include <stdlib.h>

#include "basename.h"

#if HAVE_DIRENT_H
# define HAVE_DIR 1
#else
# define HAVE_DIR 0
#endif

#include <limits.h>

/* Upper bound on the string length of an integer converted to string.
   302 / 1000 is ceil (log10 (2.0)).  Subtract 1 for the sign bit;
   add 1 for integer division truncation; add 1 more for a minus sign.  */
#define INT_STRLEN_BOUND(t) ((sizeof (t) * CHAR_BIT - 1) * 302 / 1000 + 2)

/* ISDIGIT differs from isdigit, as follows:
   - Its arg may be any int or unsigned int; it need not be an unsigned char.
   - It's guaranteed to evaluate its argument exactly once.
   - It's typically faster.
   Posix 1003.2-1992 section 2.5.2.1 page 50 lines 1556-1558 says that
   only '0' through '9' are digits.  Prefer ISDIGIT to isdigit unless
   it's important to use the locale's definition of `digit' even when the
   host does not conform to Posix.  */
#define ISDIGIT(c) ((unsigned) (c) - '0' <= 9)

#if D_INO_IN_DIRENT
# define REAL_DIR_ENTRY(dp) ((dp)->d_ino != 0)
#else
# define REAL_DIR_ENTRY(dp) 1
#endif

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

#if HAVE_DIR
static int max_backup_version (const char *, const char *);
static int version_number (const char *, const char *, size_t);
#endif

/* 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 (const char *file, enum backup_type backup_type)
{
  size_t backup_suffix_size_max;
  size_t file_len = strlen (file);
  size_t numbered_suffix_size_max = INT_STRLEN_BOUND (int) + 4;
  char *s;
  const char *suffix = simple_backup_suffix;

  /* Allow room for simple or `.~N~' backups.  */
  backup_suffix_size_max = strlen (simple_backup_suffix) + 1;
  if (HAVE_DIR && backup_suffix_size_max < numbered_suffix_size_max)
    backup_suffix_size_max = numbered_suffix_size_max;

  s = malloc (file_len + backup_suffix_size_max + numbered_suffix_size_max);
  if (s)
    {
      strcpy (s, file);

#if HAVE_DIR
      if (backup_type != simple)
	{
	  int highest_backup;
	  size_t dir_len = basename (s) - s;

	  strcpy (s + dir_len, ".");
	  highest_backup = max_backup_version (file + dir_len, s);
	  if (! (backup_type == numbered_existing && highest_backup == 0))
	    {
	      char *numbered_suffix = s + (file_len + backup_suffix_size_max);
	      sprintf (numbered_suffix, ".~%d~", highest_backup + 1);
	      suffix = numbered_suffix;
	    }
	  strcpy (s, file);
	}
#endif /* HAVE_DIR */

      addext (s, suffix, '~');
    }
  return s;
}

#if HAVE_DIR

/* 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.
   */

static int
max_backup_version (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) || strlen (dp->d_name) < file_name_length + 4)
	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;
}

/* If BACKUP is a numbered backup of BASE, return its version number;
   otherwise return 0.  BASE_LENGTH is the length of BASE.
   */

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

  version = 0;
  if (strncmp (base, backup, base_length) == 0
      && backup[base_length] == '.'
      && backup[base_length + 1] == '~')
    {
      for (p = &backup[base_length + 2]; ISDIGIT (*p); ++p)
	version = version * 10 + *p - '0';
      if (p[0] != '~' || p[1])
	version = 0;
    }
  return version;
}
#endif /* HAVE_DIR */

static const char * const backup_args[] =
{
  /* In a series of synonyms, present the most meaning full first, so
     that argmatch_valid be more readable. */
  "none", "off",
  "simple", "never",
  "existing", "nil",
  "numbered", "t",
  0
};

static const enum backup_type backup_types[] =
{
  none, none,
  simple, simple,
  numbered_existing, numbered_existing,
  numbered, numbered
};

/* Return the type of backup specified by VERSION.
   If VERSION is NULL or the empty string, return numbered_existing.
   If VERSION is invalid or ambiguous, fail with a diagnostic appropriate
   for the specified CONTEXT.  Unambiguous abbreviations are accepted.  */

enum backup_type
get_version (const char *context, const char *version)
{
  if (version == 0 || *version == 0)
    return numbered_existing;
  else
    return XARGMATCH (context, version, backup_args, backup_types);
}


/* Return the type of backup specified by VERSION.
   If VERSION is NULL, use the value of the envvar VERSION_CONTROL.
   If the specified string is invalid or ambiguous, fail with a diagnostic
   appropriate for the specified CONTEXT.
   Unambiguous abbreviations are accepted.  */

enum backup_type
xget_version (const char *context, const char *version)
{
  if (version && *version)
    return get_version (context, version);
  else
    return get_version ("$VERSION_CONTROL", getenv ("VERSION_CONTROL"));
}