import java.util.HashSet;
import java.util.Set;

public class StudentManager {

    private Set<String> computerScienceStudents;
    private Set<String> competitionStudents;


    public StudentManager() {

        computerScienceStudents = new HashSet<>();
        competitionStudents = new HashSet<>();
        populateCSSet();

    }

    private void populateCSSet(){
        computerScienceStudents.add("stu001");
        computerScienceStudents.add("stu002");
        computerScienceStudents.add("stu01");
        computerScienceStudents.add("stu101");
        computerScienceStudents.add("stu111");
        computerScienceStudents.add("stu201");
        computerScienceStudents.add("stu361");
        computerScienceStudents.add("stu398");
        computerScienceStudents.add("stu401");
    }

    public String registerCompetitionStudent(String id) {

        //if the set doesn't contain id, return msg
        if(!computerScienceStudents.contains(id)) {
            return "Registration invalid";
        }else {
            //add the id to the set and return msg
            competitionStudents.add(id);//returned boolean not used
            return "Registration Complete";
        }
    }

    public String removeCompetitionStudent(String id) {

        boolean removed = competitionStudents.remove(id);
        //if not removed, doesn't exist, return false
        if(!removed)
            return "ID Not found";
        else
            return "Student successfully removed";
    }

    public Set<String> getComputerScienceStudents() {

        return computerScienceStudents;

    }

    public Set<String> getCompetitionStudents() {

        return competitionStudents;

    }

}