/* backup.c -- make Emacs style backup file names
   Copyright (C) 1992 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it without restriction.

   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.



   GNU/Emacs style backups --
   This behaviour is controlled by two environment variables,
   VERSION_CONTROL and SIMPLE_BACKUP_SUFFIX.

   VERSION_CONTROL determines what kinds of backups are made.  If it's
   value is "numbered", then the first modification of some file
   "eraserhead.c" will yield a backup file "eraserhead.c.~1~", the
   second modification will yield "eraserhead.c.~2~", and so on.  It
   does not matter if the version numbers are not a sequence;  the next
   version will be one greater than the highest in that directory.

   If the value of VERSION_CONTROL is "numbered_existing", then such
   numbered backups will be made if there are already numbered backup
   versions of the file.  Otherwise, the backup name will be that of
   the original file with "~" (tilde) appended.  E.g., "eraserhead.c~".

   If the value of VERSION_CONTROL is "simple", then the backup name
   will be that of the original file with "~" appended, regardless of
   whether or not there exist numbered versions in the directory.

   For simple backups, the value of SIMPLE_BACKUP_SUFFIX will be used
   rather than "~" if it is set.

   If VERSION_CONTROL is unset, "numbered_existing" is assumed.  For
   Emacs lovers, "nil" is equivalent to "numbered_existing" and "t" is
   equivalent to "numbered".

   Finally, if VERSION_CONTROL is "none" or "never", backups are not
   made.  I suggest you avoid this behaviour. */

/* Written by jla, based on code from djm (see `patch') */

#include "backup.h"
#include "sys.h"
#include <ctype.h>

#ifndef isascii
#define ISDIGIT(c) (isdigit ((unsigned char) (c)))
#else
#define ISDIGIT(c) (isascii (c) && isdigit (c))
#endif

#ifndef NODIR

#include <sys/types.h>

#ifdef DIRENT
#include <dirent.h>
#ifdef direct
#undef direct
#endif
#define direct dirent
#define NLENGTH(direct) (strlen((direct)->d_name))
#else /* !DIRENT */
#define NLENGTH(direct) ((direct)->d_namlen)
#ifdef USG
#ifdef SYSNDIR
#include <sys/ndir.h>
#else /* !SYSNDIR */
#include <ndir.h>
#endif /* !SYSNDIR */
#else /* !USG */
#include <sys/dir.h>
#endif /* !USG */
#endif /* !DIRENT */

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

#if defined (_POSIX_VERSION)	/* Might be defined in unistd.h.  */
/* 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

#else /* NODIR */
#define generate_backup_filename(v,f) simple_backup_name((f))
#endif /* NODIR */

/* Default backup file suffix to use */
char *simple_backup_suffix = "~";

/* What kinds of backup files to make -- see
   table `version_control_values' below. */
enum backup_mode version_control = unknown;


/* Construct a simple backup name for PATHNAME by appending
   the value of `simple_backup_suffix'. */

static char *
simple_backup_name (pathname)
     char *pathname;
{
  char *backup_name;

  backup_name = xmalloc (strlen (pathname)
			 + strlen (simple_backup_suffix) + 2);
  sprintf (backup_name, "%s%s", pathname, simple_backup_suffix);
  return backup_name;
}

#ifndef NODIR
/* If DIRENTRY is a numbered backup version of file BASE, return
   that number.  BASE_LENGTH is the string length of BASE. */

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

  version = 0;
  if (!strncmp (base, direntry, base_length)
      && ISDIGIT (direntry[base_length + 2]))
    {
      for (p = &direntry[base_length + 2]; ISDIGIT (*p); ++p)
	version = version * 10 + *p - '0';
      if (p[0] != '~' || p[1])
	version = 0;
    }

  return version;
}


/* Return the highest version of file FILENAME in directory
   DIRNAME.  Return 0 if there are no numbered versions. */

static int
highest_version (filename, dirname)
     char *filename, *dirname;
{
  DIR *dirp;
  struct direct *dp;
  int highest_version;
  int this_version;
  int file_name_length;

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

  highest_version = 0;
  file_name_length = strlen (filename);

  while ((dp = readdir (dirp)) != 0)
    {
      if (!REAL_DIR_ENTRY (dp) || NLENGTH (dp) <= file_name_length + 2)
	continue;

      this_version = version_number (filename, dp->d_name, file_name_length);
      if (this_version > highest_version)
	highest_version = this_version;
    }

  closedir (dirp);
  return highest_version;
}


/* Return the highest version number for file PATHNAME.  If there
   are no backups, or only a simple backup, return 0. */

static int
max_version (pathname)
     char *pathname;
{
  register char *p;
  register char *filename;
  int pathlen = strlen (pathname);
  int version;

  p = pathname + pathlen - 1;
  while (p > pathname && *p != '/')
    p--;

  if (*p == '/')
    {
      int dirlen = p - pathname;
      register char *dirname;

      filename = p + 1;
      dirname = xmalloc (dirlen + 1);
      strncpy (dirname, pathname, (dirlen));
      dirname[dirlen] = '\0';
      version = highest_version (filename, dirname);
      free (dirname);
      return version;
    }

  filename = pathname;
  version = highest_version (filename, ".");
  return version;
}


/* Generate a backup filename for PATHNAME, dependent on the
   value of VERSION_CONTROL. */

static char *
generate_backup_filename (version_control, pathname)
     enum backup_mode version_control;
     char *pathname;
{
  int last_numbered_version;
  char *backup_name;

  if (version_control == none)
    return 0;

  if (version_control == simple)
    return simple_backup_name (pathname);

  last_numbered_version = max_version (pathname);
  if (version_control == numbered_existing
      && last_numbered_version == 0)
    return simple_backup_name (pathname);

  last_numbered_version++;
  backup_name = xmalloc (strlen (pathname) + 16);
  if (!backup_name)
    return 0;

  sprintf (backup_name, "%s.~%d~", pathname, last_numbered_version);
  return backup_name;
}

#endif /* !NODIR */

static struct version_control_values values[] =
{
  {none, "never"},		/* Don't make backups. */
  {simple, "simple"},		/* Only simple backups */
  {numbered_existing, "existing"},	/* Numbered if they already exist */
  {numbered_existing, "nil"},	/* Ditto */
  {numbered, "numbered"},	/* Numbered backups */
  {numbered, "t"},		/* Ditto */
  {unknown, 0}			/* Initial, undefined value. */
};


extern char *getenv ();

/* Determine the value of `version_control' by looking in the
   environment variable "VERSION_CONTROL".  Defaults to
   numbered_existing. */

enum backup_mode
version_control_value ()
{
  char *version;
  struct version_control_values *v;

  version = getenv ("VERSION_CONTROL");
  if (version == 0 || *version == 0)
    return numbered_existing;

  v = &values[0];
  while (v->name)
    {
      if (strcmp (version, v->name) == 0)
	return v->value;
      v++;
    }

  return unknown;
}


/* Initialize information used in determining backup filenames. */

void
initialize_backups ()
{
  char *v = getenv ("SIMPLE_BACKUP_SUFFIX");

  if (v && *v)
    simple_backup_suffix = v;
#ifdef NODIR
  version_control = simple;
#else /* !NODIR */
  version_control = version_control_value ();
  if (version_control == unknown)
    {
      fprintf (stderr, "indent:  Strange version-control value\n");
      fprintf (stderr, "indent:  Using numbered-existing\n");
      version_control = numbered_existing;
    }
#endif /* !NODIR */
}

/* Prints an error message using `perror' */
extern void sys_error ();

/* Make a backup copy of FILE, taking into account version-control.
   See the description at the beginning of the file for details. */

void
make_backup (file)
     struct file_buffer *file;
{
  int fd;
  register char *p = file->name + strlen (file->name) - 1;
  char *backup_filename;
  char *new_backup_name;

  backup_filename = generate_backup_filename (version_control, file->name);
  if (!backup_filename)
    {
      fprintf (stderr, "indent: Can't make backup filename of %s", file->name);
      exit (1);
    }

  fd = creat (backup_filename, 0666);
  if (fd < 0)
    sys_error (backup_filename);
  if (write (fd, file->data, file->size) != file->size)
    sys_error (backup_filename);

  close (fd);
  free (backup_filename);
}