/* backupfile.c -- make Emacs style backup file names
   Copyright (C) 1990-2003, 2005-2006, 2012, 2020 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 3 of the License, 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, see <https://www.gnu.org/licenses/>.  */

/* 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-lgpl.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 = (char *) 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 = last_component (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"));
}