#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <pwd.h>
#include <errno.h>
#include <err.h>
#include <shadow.h>
int
main(int argc, char *argv[])
{
	char uname[255]; // username
	char pass[255]; // array for copying password
	char *p, *ptr;
	int len; // uname length
	struct passwd *pwd;
	struct spwd *spwd;
 
	setbuf(stdout, NULL);
 
	while (1) {
		printf("username: ");
		// clear EOF in stdin, if exists!
		clearerr(stdin);
 
		p = fgets(uname, sizeof(uname), stdin);
		if (p == NULL || *p == '\0') {
			putchar('\n');
			continue;
		}
 
		len = strlen(uname);
		if (uname[len - 1] == '\n')
			uname[len - 1] = '\0';
 
		if (!strlen(uname)) {
			putchar('\n');
			continue;
		}
 
		// clear EOF in stdin
		clearerr(stdin);
 
		p = getpass("password: ");
		if (p == NULL || *p == '\0') {
			continue;
		}
 
		ptr = strncpy(pass, p, strlen(p) + 1);
		if (ptr == NULL) {
			fprintf(stderr, "\nstrncpy error\n");
			continue;
		}
 
		while(*p != '\0')
			*p++ = '\0';
 
		errno = 0;
		pwd = getpwnam(uname);
		if (pwd == NULL) {
			if (errno) {
				perror(NULL);
				continue;
			}
 
			fprintf(stderr, "%s user not exists\n", uname);
			continue;
		}
 
		errno = 0;
		spwd = getspnam(uname);
		if (spwd == NULL) {
			if (errno) {
				perror(NULL);
				continue;
			}
 
			fprintf(stderr, "%s user not exists\n", uname);
			continue;
		}
 
		p = crypt(pass, spwd->sp_pwdp);
 
		if (strcmp(p, spwd->sp_pwdp) != 0) {
			printf("Incorrect username or password.\n");
			continue;
		}
 
		exit(EXIT_SUCCESS);
	}
}