#include <stdio.h>
#include <stdlib.h>
#include <utmp.h>
#include <getopt.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>

int main(int argc, char **argv) {
        struct utmp *handler;
        struct passwd *passwdRecord;
        struct group *groupNameRecord;
        int groupsCount;
        int gFlag = 0;
        int hFlag = 0;
        int c;
        while((c = getopt (argc, argv, "hg")) != -1) {
                switch(c) {
                        case 'h':
                                hFlag = 1;
                                break;
                        case 'g':
                                gFlag = 1;
                                break;
                        default:
                                abort();
                }
        }
        handler = getutent();
        while(handler != NULL) {
                if(handler->ut_type == 7) {
                        passwdRecord = getpwnam(handler->ut_user);
                        printf("%s ", handler->ut_user);
                        if(hFlag) printf("(%s) ", handler->ut_host);
                        if(gFlag) {
                                groupsCount = 0;
                                getgrouplist(handler->ut_user, passwdRecord->pw_gid, NULL, &groupsCount);
                                gid_t *userGroups = (gid_t*)malloc(groupsCount * sizeof(gid_t));
                                getgrouplist(handler->ut_user, passwdRecord->pw_gid, userGroups, &groupsCount);
                                printf("[");
                                for (int i=0; i<groupsCount; i++) {
                                        groupNameRecord= getgrgid(userGroups[i]);
                                        printf("%s ", groupNameRecord->gr_name);
                                }
                                printf("]");
                                free(userGroups);
                        }
                }
        }
return 0;
}