/*
 * UNG's Not GNU
 *
 * Copyright (c) 2020 Jakob Kaivo <jkk@ung.org>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#define _POSIX_C_SOURCE 200809L
#include <fcntl.h>
#include <dirent.h>
#include <limits.h>
#include <pwd.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

#ifndef LINE_MAX
#define LINE_MAX _POSIX2_LINE_MAX
#endif

#ifndef O_SEARCH
#define O_SEARCH 0
#endif

#define USERS_DIRECTORY "/var/secure/users"
static DIR *users_dir = NULL;

struct user {
	struct passwd pw;
	char gecos[LINE_MAX];
	char password[LINE_MAX];
};

enum selection { UID, NAME, ALL };

static struct user *user_read(char *name)
{
	static struct user u = { 0 };

	int user = openat(dirfd(users_dir), name, O_SEARCH);
	if (user == -1) {
		return NULL;
	}

	struct stat st;
	if (fstat(user, &st) != 0) {
		close(user);
		return NULL;
	}

	u.pw.pw_name = name;
	u.pw.pw_uid = st.st_uid;
	u.pw.pw_gid = st.st_gid;
	u.pw.pw_dir = "/";		// TODO: read symlink at userfd, home
	u.pw.pw_shell = "/bin/sh";	// TOOD: read symlink at userfd, shell
	strcpy(u.gecos, name); 		// TODO: read file at userfd, gecos
	strcpy(u.password, "--");	// TODO: read file at userfd, password

	close(user);

	return &u;
}

static char *user_uid(uid_t uid)
{
	char *name = NULL;

	struct dirent *de;
	while ((de = readdir(users_dir)) != NULL) {
		if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, "..")) {
			continue;
		}

		struct stat st;
		if (fstatat(dirfd(users_dir), de->d_name, &st, 0) != 0) {
			continue;
		}

		if (st.st_uid == uid) {
			name = de->d_name;
			break;
		}
	}

	return name;
}

static struct user *user_find(enum selection sel, char *name, uid_t uid)
{
	if (sel == UID) {
		name = user_uid(uid);
	}

	return user_read(name);
}

static void user_print(const struct user *u)
{
	if (u == NULL) {
		return;
	}

	printf("%s:%s:%jd:%jd:%s:%s:%s\n", u->pw.pw_name, u->password,
		(intmax_t)u->pw.pw_uid, (intmax_t)u->pw.pw_gid,
		u->gecos, u->pw.pw_dir, u->pw.pw_shell);
}

int main(int argc, char *argv[])
{
	char *name = getlogin();
	uid_t uid = getuid();
	enum selection sel = NAME;;
	enum { LIST, PASSWORD } action = LIST;

	int c;
	while ((c = getopt(argc, argv, "LN:U:p")) != -1) {
		switch (c) {
		case 'L':
			sel = ALL;
			break;

		case 'N':
			sel = NAME;
			name = optarg;
			break;

		case 'U':
			sel = UID;
			uid = atoi(optarg);
			break;

		case 'p':
			action = PASSWORD;
			break;

		default:
			return 1;
		}
	}

	if (action == PASSWORD && sel == ALL) {
		fprintf(stderr, "user: -L and -p are incompatible\n");
		return 1;
	}

	users_dir = opendir(USERS_DIRECTORY);
	if (users_dir == NULL) {
		fprintf(stderr, "user: no users directory\n");
		return 1;
	}

	if (action == PASSWORD) {
		printf("TODO: interactively change password\n");
		return 0;
	}

	if (sel == ALL) {
		struct dirent *de = NULL;
		while ((de = readdir(users_dir)) != NULL) {
			if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, "..")) {
				continue;
			}
			user_print(user_read(de->d_name));
		}
		return 0;
	}

	struct user *u = user_find(sel, name, uid);
	if (u == NULL) {
		fprintf(stderr, "user: not found\n");
		return 1;
	}
	user_print(u);
}