/*
 * $Id$
 * 
 * Copyright (c) 2001 Michal Moskal <malekith@pld-linux.org>.
 * Copyright (c) 2009 Jan Rękorajski <baggins@pld-linux.org>.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by Michal Moskal.
 * 4. Neither the name of the author nor the names of any co-contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY MICHAL MOSKAL AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *
 * 
 * USAGE: grouprename old-name new-name
 *
 * Change the name of a group from old-name to new-name,
 * It is usable as part of setup package, during upgrade in case a group name
 * has to change. If new-name is already found in system database or old-name
 * is not found, nothing changes,. UIDs/GIDs are *not* checked anyhow. 
 *
 * Written for PLD Linux (http://www.pld-linux.org/) setup package.
 *
 * Compilation against uClibc:
 * UCROOT=/usr/lib/bootdisk/usr
 * gcc -I$UCROOT/include -nostdlib -O2 grouprename.c $UCROOT/lib/crt0.o \
 * 		$UCROOT/lib/libc.a -lgcc -o grouprename
 * strip -R .comment -R .note grouprename
 *
 * Shamelss ripoff of the joinpasswd.c program
 * 
 */

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h> // for rename(2)
#include <string.h>
#include <signal.h>

#define FILE3 "/etc/group"
#define FILE4 "/etc/gshadow"

/* #define OLD_LOCK */

#define LOCK_FILE "/etc/.pwd.lock"

/* maybe "-" or sth? */
#define BACKUP ".old"

/* #define SILENT */

void eputs(const char *msg)
{
	write(2, msg, strlen(msg));
}

void fatal(const char *msg)
{
	eputs(msg);
	eputs("\n");
	exit(1);
}

char *map_file(const char *name, int *sz, int *mfd)
{
	int fd;
	void *ptr;
	struct stat st;

	fd = open(name, O_RDONLY);
	if (fd == -1)
		return NULL;
	*mfd = fd;
	fstat(fd, &st);
	*sz = st.st_size;
	ptr = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
	if (ptr == MAP_FAILED)
		return NULL;

	return ptr;
}

int exist(char *id, int id_len, char *ptr, int sz)
{
	int i;

	for (i = 0; i < sz; ) {
		if (sz - i > id_len && memcmp(id, ptr, id_len) == 0)
			return 1;
		while (i < sz && ptr[i] != '\n')
			i++;
		i++;
	}

	return 0;
}

void itoa(char *buf, long i)
{
	char tmp[32];
	char *p;

	if (i < 0) {
		strcpy(buf, "-");
		buf++;
		i = -i;
	}
	if (i == 0) {
		strcpy(buf, "0"); 
		return;
	}
	for (p = tmp; i; i /= 10)
		*p++ = (i % 10) + '0';
	while (p > tmp)
		*buf++ = *--p;
	*buf = 0;
}

#ifndef OLD_LOCK
int lock_fd = -1;
void noop(int x)
{
	(void)x;
}
#endif

int try_lock(const char *name)
{
#ifdef OLD_LOCK
	char file[strlen(name) + 32], lock[strlen(name) + 32];
	char buf[32];
	int fd;
	long pid;

	strcpy(lock, name);
	strcpy(file, name);
	strcat(lock, ".lock");
	itoa(buf, (long)getpid());
	strcat(file, ".");
	strcat(file, buf);
	
	fd = open(file, O_WRONLY|O_CREAT|O_EXCL|O_TRUNC, 0600);
	if (fd < 0)
		return -1;
	write(fd, buf, strlen(buf));
	close(fd);

	if (link(file, lock) == 0) {
		unlink(file);
		return 0;
	}

	fd = open(lock, O_RDONLY);
	if (fd < 0)
		goto oops;
	memset(buf, 0, sizeof(buf));
	read(fd, buf, sizeof(buf));
	pid = atol(buf);
	if (pid == 0 || kill(pid, 0) != 0) {
		/* stale lock */
		unlink(file);
		unlink(lock);
		/* try again */
		return try_lock(name);
	}

oops:
	unlink(file);
	return -1;
#else
	struct flock fl;
	
	if (lock_fd != -1)
		return -1;
	lock_fd = open(LOCK_FILE, O_RDWR|O_CREAT, 0600);
	if (lock_fd == -1)
		return -1;
	signal(SIGALRM, noop);
	alarm(15);
	memset(&fl, 0, sizeof(fl));
	fl.l_type = F_WRLCK;
	fl.l_whence = SEEK_SET;
	if (fcntl(lock_fd, F_SETLKW, &fl) != 0) {
		alarm(0);
		close(lock_fd);
		lock_fd = -1;
		return -1;
	}
	alarm(0);
	
	return 0;
#endif
}

void unlock(const char *name)
{
#ifdef OLD_LOCK
	char lock[strlen(name) + 32];

	strcpy(lock, name);
	strcat(lock, ".lock");
	unlink(lock);
#else
	if (lock_fd != -1)
		close(lock_fd);
	lock_fd = -1;
#endif
}

void lock(const char *name)
{
	int n;

	n = 5;
	while (n--) {
		if (try_lock(name) == 0)
			return;
		eputs("waiting for lock...\n");
		sleep(1);
	}
	fatal("cannot get lock");
}

int join(const char *oldgr, const char *newgr, const char *name, const char *backup)
{
	char *old, *id;
	int i, fd, mfd;
	int sz;

//	lock(name);
	old = map_file(name, &sz, &mfd);
	if (old == NULL)
		fatal("cannot mmap old");

	fd = open(backup, O_WRONLY|O_CREAT|O_TRUNC, 0600);
	if (fd < 0)
		fatal("cannot make backup");
	write(fd, old, sz);
	close(fd);

	munmap(old, sz);
	close(mfd);

#ifndef SILENT
	eputs("working on `");
	eputs(name);
	eputs("'\n");
#endif /* SILENT */

	old = map_file(backup, &sz, &mfd);
	if (old == NULL)
		fatal("cannot mmap backup");

	fd = open(name, O_CREAT|O_WRONLY|O_TRUNC, 0644);
	if (fd < 0)
		fatal("cannot open new file");
	
	for (i = 0; i < sz; ) {
		id = old + i;
		while (i < sz && old[i] != ':' && old[i] != '\n')
			i++;
		if (i < sz && old[i] == ':') {
			int id_len, line_len;
			char *rem = old + i;

			id_len = i - (id - old);
			while (i < sz && old[i] != '\n')
				i++;
			if (i < sz)
				i++;
			line_len = i - (rem - old);

			if (id_len == strlen(oldgr) &&
					memcmp(id, oldgr, id_len) == 0) {
#ifndef SILENT
				eputs(oldgr);
				eputs(": ranaming to `");
				eputs(newgr);
				eputs("'\n");
#endif /* SILENT */
				write(fd, newgr, strlen(newgr));
			} else
				write(fd, id, id_len);
			write(fd, rem, line_len);
		} else if (i < sz)
			i++;
	}
	close(fd);

	munmap(old, sz);
	close(mfd);

//	unlock(name);

	return 0;
}

int main(int argc, const char *argv[])
{
	const char *oldgr, *newgr;

	if (argc != 3) {
		eputs("Usage: grouprename old-name new-name");
		return 1;
	}
	oldgr = argv[1];
	newgr = argv[2];

#if 0
	join(oldgr, newgr, FILE3, FILE3 BACKUP);
	join(oldgr, newgr, FILE4, FILE4 BACKUP);
#else
	join(oldgr, newgr, "test", "test.old");
#endif
	return 0;
}