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rcsid[] and sccsid[] and copyright[] are essentially unmaintained (and
unmaintainable).  these days, people use source.  these id's do not provide
any benefit, and do hurt the small install media
(the 33,000 line diff is essentially mechanical)
ok with the idea millert, ok dms

/*	$OpenBSD: backupfile.c,v 1.20 2009/10/27 23:59:41 deraadt Exp $	*/

/*
 * 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
 * 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.
 */

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

#include <ctype.h>
#include <dirent.h>
#include <libgen.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "backupfile.h"


#define ISDIGIT(c) (isascii (c) && isdigit (c))

/* 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(const char *, const char *);
static char	*make_version_name(const char *, int);
static int	max_backup_version(const char *, const char *);
static int	version_number(const char *, const char *, size_t);
static int	argmatch(const char *, const char **);
static void	invalid_arg(const char *, const char *, int);

/*
 * 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)
{
	char	*dir, *base_versions;
	int	highest_backup;

	if (backup_type == simple)
		return concat(file, simple_backup_suffix);
	base_versions = concat(basename(file), ".~");
	if (base_versions == NULL)
		return NULL;
	dir = dirname(file);
	if (dir == NULL) {
		free(base_versions);
		return NULL;
	}
	highest_backup = max_backup_version(base_versions, dir);
	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(const char *file, const char *dir)
{
	DIR	*dirp;
	struct dirent	*dp;
	int	highest_version, this_version;
	size_t	file_name_length;

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

	highest_version = 0;
	file_name_length = strlen(file);

	while ((dp = readdir(dirp)) != NULL) {
		if (dp->d_namlen <= file_name_length)
			continue;

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

/*
 * Return a string, allocated with malloc, containing "FILE.~VERSION~".
 * Return 0 if out of memory.
 */
static char *
make_version_name(const char *file, int version)
{
	char	*backup_name;

	if (asprintf(&backup_name, "%s.~%d~", file, version) == -1)
		return NULL;
	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(const char *base, const char *backup, size_t 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(const char *str1, const char *str2)
{
	char	*newstr;

	if (asprintf(&newstr, "%s%s", str1, str2) == -1)
		return NULL;
	return newstr;
}

/*
 * If ARG is an unambiguous match for an element of the null-terminated array
 * OPTLIST, return the index in OPTLIST of the matched element, else -1 if it
 * does not match any element or -2 if it is ambiguous (is a prefix of more
 * than one element).
 */
static int
argmatch(const char *arg, const char **optlist)
{
	int	i;	/* Temporary index in OPTLIST. */
	size_t	arglen;	/* Length of ARG. */
	int	matchind = -1;	/* Index of first nonexact match. */
	int	ambiguous = 0;	/* If nonzero, multiple nonexact match(es). */

	arglen = strlen(arg);

	/* Test all elements for either exact match or abbreviated matches.  */
	for (i = 0; optlist[i]; i++) {
		if (!strncmp(optlist[i], arg, arglen)) {
			if (strlen(optlist[i]) == arglen)
				/* Exact match found.  */
				return i;
			else if (matchind == -1)
				/* First nonexact match found.  */
				matchind = i;
			else
				/* Second nonexact match found.  */
				ambiguous = 1;
		}
	}
	if (ambiguous)
		return -2;
	else
		return matchind;
}

/*
 * Error reporting for argmatch. KIND is a description of the type of entity
 * that was being matched. VALUE is the invalid value that was given. PROBLEM
 * is the return value from argmatch.
 */
static void
invalid_arg(const char *kind, const char *value, int problem)
{
	fprintf(stderr, "patch: ");
	if (problem == -1)
		fprintf(stderr, "invalid");
	else			/* Assume -2. */
		fprintf(stderr, "ambiguous");
	fprintf(stderr, " %s `%s'\n", kind, value);
}

static const char *backup_args[] = {
	"never", "simple", "nil", "existing", "t", "numbered", 0
};

static enum backup_type backup_types[] = {
	simple, simple, numbered_existing,
	numbered_existing, numbered, numbered
};

/*
 * Return the type of backup indicated by VERSION. Unique abbreviations are
 * accepted.
 */
enum backup_type
get_version(const char *version)
{
	int	i;

	if (version == NULL || *version == '\0')
		return numbered_existing;
	i = argmatch(version, backup_args);
	if (i >= 0)
		return backup_types[i];
	invalid_arg("version control type", version, i);
	exit(2);
}