/*      $OpenBSD: backupfile.c,v 1.23 2024/03/22 19:22:23 jcs 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, *tmp_file;
        int     highest_backup;

        if (backup_type == simple)
                return concat(file, simple_backup_suffix);
        tmp_file = strdup(file);
        if (tmp_file == NULL)
                return NULL;
        base_versions = concat(basename(tmp_file), ".~");
        free(tmp_file);
        if (base_versions == NULL)
                return NULL;
        tmp_file = strdup(file);
        if (tmp_file == NULL) {
                free(base_versions);
                return NULL;
        }
        dir = dirname(tmp_file);
        if (dir == NULL) {
                free(base_versions);
                free(tmp_file);
                return NULL;
        }
        highest_backup = max_backup_version(base_versions, dir);
        free(base_versions);
        free(tmp_file);
        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((unsigned char)backup[base_length])) {
                for (p = &backup[base_length]; ISDIGIT((unsigned char)*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[] = {
        "none", "never", "simple", "nil", "existing", "t", "numbered", 0
};

static enum backup_type backup_types[] = {
        none, 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);
}