#define _GNU_SOURCE

#include <sys/types.h>

#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>

#include <stdbool.h>

#include <string.h>

#include <grp.h>

#include <pwd.h>

#include <errno.h>

#include <signal.h>

#ifdef __midipix__

#include <windows.h>

#define IFLAG 1

#define WFLAG 1

#else

#define IFLAG 0

#define WFLAG 0

#endif

#include "login.h"

static char* get_win32_username(void)

{

#ifdef __midipix__

	size_t i;

	char usernam[257];

	unsigned int usernam_siz = sizeof(usernam);

	if(GetUserNameA(usernam, &usernam_siz) == 0)

		return "";

	for(i = 0; i < 257; i++)

		usernam[i] = tolower(usernam[i]);

	return strdup(usernam);

#else

	return "";

#endif

}

/* force memset */

static void __attribute__((optimize("O0"))) memset_noopt(void* mem, int c, size_t memsiz)

{

	memset(mem, c, memsiz);

}

static bool switch_user_context(struct passwd* pw, const char* username)

{

	/* temporary */

	#ifdef INSECURE

	if(initgroups(username, pw->pw_gid) == -1) {

		printf("initgroups failed: %s", strerror(errno));

		exit(1);

	}

	#endif

	#ifdef INSECURE

		if((setuid(pw->pw_uid) != -1) && (setgid(pw->pw_gid) != -1))

			return true;

		return false;

	#else

	gid_t oldgid = getegid();

	uid_t olduid = geteuid();

	if((setegid(pw->pw_gid) != -1) && (setgid(pw->pw_gid) != -1) && (seteuid(pw->pw_uid) != -1) && (setuid(pw->pw_uid) != -1)) {

		gid_t newgid = getgid();

		uid_t newuid = getuid();

		#ifdef debug

		printf("old gid %d\n", oldgid);

		printf("old uid %d\n", olduid);

		printf("new gid %d\n", newgid);

		printf("new uid %d\n", newuid);

		#endif

		if((newgid == oldgid) && (newuid == olduid))

			return true;

	}

	return false;

	#endif

}

int main(int argc, char **argv)

{

	/* we don't want ^D etc to mess up the logic */

	(void)signal(SIGTSTP, SIG_IGN);

	(void)signal(SIGQUIT, SIG_IGN);

	(void)signal(SIGINT, SIG_IGN);

	struct passwd *pwd;

	char* username = NULL;

	int c;

	bool authenticated = false;

	int pflag, fflag, iflag, wflag = 0;

	while((c = getopt(argc, argv, "pfh:iw")) != -1)

		switch(c) {

			case 'p':

				pflag = 1; break;

			case 'f':

				fflag = 1; break; /* unused, pointless currently */

			case 'h':

				if(getuid()) {

					exit(1);

				}

				break;

			case 'i':

				iflag = IFLAG; break;

			case 'w':

				wflag = WFLAG; break;

			default:

			case '?':

				usage();

				break;

		}

		argv += optind;

	if(wflag)

		username = get_win32_username();

	else if(*argv)

		username = *argv;

	else {

		/* TODO: hostname, emulate shadow's login(1) prompt */

		printf("login: ");

		fflush(0);

		(void)scanf("%ms", &username);

	}

	pwd = getpwnam(username);

	if(!iflag)

	{

		char* pw = getpass("Password: ");

		if(pwd) {

			/* if hash == 0 then authenticated = true */

			if(*pwd->pw_passwd == '\0') {

				authenticated = true;

			}

			else if(pw) {

				char* pw_encrypted = crypt(pw, pwd->pw_passwd);

				if(!timingsafe_memcmp(pw_encrypted, pwd->pw_passwd, strlen(pw_encrypted)))

					authenticated = true;

			}

			else {

				puts("not authenticated");

				authenticated = false;

			}

		} else {

			authenticated = false;

		}

		memset_noopt(pw, 0, strlen(pw));

	} else

		authenticated = true; /* iflag */

	endpwent();

	if(!authenticated) {

		puts("Login incorrect.");

		exit(1);

	}

	/* authenticated, attempt to set user context and spawn user shell */

	if(switch_user_context(pwd, username)) {

		if(*pwd->pw_shell == '\0')

			pwd->pw_shell = "/bin/sh"; /* if /bin/sh doesn't exist, I do not care. blow up. */

		if(chdir(pwd->pw_dir) < 0) {

			printf("no home directory %s!\n", pwd->pw_dir); // handle -EPERM, -ENOMEM, -ESYMLNK

				if(chdir("/") == -1) {

					printf("chdir failed with %s", strerror(errno));

					exit(1); /* no-one can save you now */

				}

			pwd->pw_dir = "/";

		}

		if(!pflag)

			(void)clearenv();

		(void)setenv("HOME", pwd->pw_dir, 1);

		(void)setenv("SHELL", pwd->pw_shell, 1);

		(void)setenv("TERM", "xterm", 0); /* rrrr. needs researching */

		(void)setenv("LOGNAME", pwd->pw_name, 1);

		(void)setenv("USER", pwd->pw_name, 1);

#if 0

		(void)setenv("PS1", "$ ", 0);

#endif

		(void)setenv("PATH", "/local/sbin:/local/bin:/sbin:/bin", 0);

		execlp(pwd->pw_shell, pwd->pw_shell, (const char*)NULL);

		printf("login failed with error: %s", strerror(errno));

		exit(1);

	}

	puts("could not switch to specified user.");

}

void usage(void) {

	puts("login -i (skip authentication, only works on midipix, temporary)");

	puts("login -w (acquire username through Win32)");

	puts("login -p (preserve environment)");

	puts("login -f (no secondary authentication, unused)");

	puts("login -h (pass remote server name to login, unused)");

	exit(0);

}