#include <stdlib.h>
#include <stdio.h>
#include <utmp.h>
#include <unistd.h>
#include <pwd.h>
#include <grp.h>

int main(int argc, char **argv)
{
    int fAOpt = 0, fBOpt = 0;
    int optRes;
    int numberOfGroups;
    gid_t *groups;

    struct group *group;
    struct passwd *pass;
    struct utmp *extr;
    setutent();

    while ((optRes = getopt(argc, argv, "ab")) != -1)
    {
        switch(optRes)
        {
            case 'a':
            fAOpt = 1;
            break;

            case 'b':
            fBOpt = 1;
            break;

        }
    }



    while ((extr = getutent()) != NULL)
    {

        if(extr->ut_type == 7)
        {
            pass = getpwnam(extr->ut_user);
            numberOfGroups = 0;
            getgrouplist(extr->ut_user, pass->pw_gid, groups, &numberOfGroups);
            groups = malloc(numberOfGroups * sizeof(gid_t));
            getgrouplist(extr->ut_user, pass->pw_gid, groups, &numberOfGroups);

            if((fAOpt != 1) && (fBOpt != 1))
            printf("%s \n", extr->ut_user);
            if((fAOpt == 1) && (fBOpt != 1))
            printf("%s (%s) \n", extr->ut_user, extr->ut_host);
            if((fAOpt != 1) && (fBOpt == 1))
            {
                printf("%s [ ", extr->ut_user);
                for(int i = 0; i < numberOfGroups; i++)
                {
                    group = getgrgid(groups[i]);
                    printf("%s ", group->gr_name);
                }
                printf("]\n");

            }
            if((fAOpt == 1) && (fBOpt == 1))
            {
                printf("%s (%s) [ ", extr->ut_user, extr->ut_host);
                for(int i = 0; i < numberOfGroups; i++)
                {
                    group = getgrgid(groups[i]);
                    printf("%s ", group->gr_name);
                }
                printf("]\n");
            }
            free(groups);
        }
    }
    endutent();
    return 0;
}