/*
 * Copyright (c) 2015, 2023 Jonas 'Sortie' Termansen.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * passwd.c
 * Password change.
 */

#include <sys/termmode.h>
#include <sys/types.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <pwd.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>

static void password(char* buffer,
                     size_t buffer_size,
                     const char* whose,
                     const char* question,
                     bool require_tty)
{
	bool is_tty = isatty(0);
	if ( !require_tty && is_tty )
		errx(1, "Input is not a terminal");
	unsigned int termmode = 0;
	if ( is_tty )
	{
		gettermmode(0, &termmode);
		settermmode(0, termmode & ~TERMMODE_ECHO);
		if ( whose )
			printf("%s's ", whose);
		printf("%s ", question);
		fflush(stdout);
		fflush(stdin);
	}
	// TODO: This may leave a copy of the password in the stdio buffer.
	fgets(buffer, buffer_size, stdin);
	if ( is_tty )
	{
		fflush(stdin);
		printf("\n");
		settermmode(0, termmode);
	}
	size_t buffer_length = strlen(buffer);
	if ( buffer_length && buffer[buffer_length-1] == '\n' )
		buffer[--buffer_length] = '\0';
}

int main(int argc, char* argv[])
{
	const char* cipher = "blowfish,a";
	bool hash_password = false;

	int opt;
	while ( (opt = getopt(argc, argv, "c:H")) != -1 )
	{
		switch ( opt )
		{
		case 'c': cipher = optarg; break;
		case 'H': hash_password = true; break;
		default: return 1;
		}
	}

	if ( hash_password )
	{
		if ( argc - optind )
			errx(1, "Unexpected extra operand");
		char pass[128];
		password(pass, sizeof(pass), NULL, "Enter password (will not echo)",
		         false);
		fgets(pass, sizeof(pass), stdin);
		char newhash[128];
		if ( crypt_newhash(pass, cipher, newhash, sizeof(newhash)) < 0 )
			err(1, "crypt_newhash");
		if ( printf("%s\n", newhash) < 0 || fflush(stdout) == EOF )
			err(1, "stdout");
		return 0;
	}

	uid_t my_uid = getuid();
	char* my_username = getlogin();
	if ( !my_username )
		err(1, "failed to get username");
	if ( !(my_username = strdup(my_username)) )
		err(1, "stdup");

	const char* username;
	if ( argc - optind <= 1 )
		username = my_username;
	else if ( argc - optind <= 2 )
		username = argv[1];
	else
		errx(1, "Unexpected extra operand");

	errno = 0;
	struct passwd* pwd = getpwnam(username);
	if ( !pwd && errno == 0 )
		errx(1, "%s: No such user", username);
	if ( !pwd )
		err(1, "%s", username);

	if ( my_uid != 0 && pwd->pw_uid != my_uid )
		errx(1, "You may not change the password for '%s'", username);

	printf("Changing password for %s.\n", username);

	if ( my_uid != 0 )
	{
		char current[128];
		password(current, sizeof(current), pwd->pw_name,
		         "current password (will not echo)", true);
		if ( crypt_checkpass(current, pwd->pw_passwd) < 0 )
			errx(1, "Wrong password for '%s'", pwd->pw_name);
		explicit_bzero(current, sizeof(current));
	}

	char first[128];
	password(first, sizeof(first), NULL, "Enter new password (will not echo)",
	         true);
	char second[128];
	password(second, sizeof(second), NULL, "Enter new password (again)", true);
	if ( strcmp(first, second) != 0 )
		errx(1, "Passwords don't match");
	explicit_bzero(second, sizeof(second));
	char newhash[128];
	if ( crypt_newhash(first, cipher, newhash, sizeof(newhash)) < 0 )
		err(1, "crypt_newhash");
	explicit_bzero(first, sizeof(first));
	// TODO: This is subject to races and is obviously an insecure design.
	//       The backend and coordination of the passwd database should be moved
	//       to its own daemon.
	FILE* in = fopen("/etc/passwd", "r");
	if ( !in )
		err(1, "/etc/passwd");
	int fd = open("/etc/passwd.new", O_WRONLY | O_CREAT | O_EXCL, 0644);
	if ( fd < 0 )
		err(1, "/etc/passwd.new");
	fchown(fd, 0, 0); // HACK.
	FILE* fp = fdopen(fd, "w");
	if ( !fp )
	{
		unlink("/etc/passwd.new");
		err(1, "fdopen");
	}
	char* line = NULL;
	size_t size = 0;
	ssize_t length;
	bool found = false;
	while ( 0 < (length = getline(&line, &size, in)) )
	{
		char* copy = strdup(line);
		if ( !copy )
		{
			unlink("/etc/passwd.new");
			err(1, "malloc");
		}
		if ( copy[length - 1] == '\n' )
			copy[--length] = '\0';
		struct passwd passwd;
		if ( !scanpwent(copy, (pwd = &passwd)) )
		{
			fputs(line, fp);
			free(copy);
			continue;
		}
		fputs(pwd->pw_name, fp);
		fputc(':', fp);
		if ( !strcmp(pwd->pw_name, username) )
		{
			fputs(newhash, fp);
			found = true;
		}
		else
			fputs(pwd->pw_passwd, fp);
		fputc(':', fp);
		fprintf(fp, "%" PRIuUID, pwd->pw_uid);
		fputc(':', fp);
		fprintf(fp, "%" PRIuGID, pwd->pw_gid);
		fputc(':', fp);
		fputs(pwd->pw_gecos, fp);
		fputc(':', fp);
		fputs(pwd->pw_dir, fp);
		fputc(':', fp);
		fputs(pwd->pw_shell, fp);
		fputc('\n', fp);
		if ( ferror(fp) || fflush(stdout) == EOF )
		{
			unlink("/etc/passwd.new");
			err(1, "/etc/passwd.new");
		}
		free(copy);
	}
	free(line);
	if ( ferror(in) )
	{
		unlink("/etc/passwd.new");
		err(1, "/etc/passwd");
	}
	fclose(in);
	if ( ferror(fp) || fclose(fp) == EOF )
	{
		unlink("/etc/passwd.new");
		err(1, "/etc/passwd.new");
	}
	if ( !found )
	{
		unlink("/etc/passwd.new");
		errx(1, "user %s is not directly in /etc/passwd", username);
	}
	if ( rename("/etc/passwd.new", "/etc/passwd") < 0 )
	{
		unlink("/etc/passwd.new");
		err(1, "rename: /etc/passwd.new -> /etc/passwd");
	}

	printf("Changed password for %s.\n", username);

	return 0;
}