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

/**
 * Write a description of class SchoolClass here.
 *
 * @author (your name)
 * @version (a version number or a date)
 */
public class SchoolClass
{
    private String name;
    private Set<Student> students = new HashSet<Student>();

    public SchoolClass(String name){
        if(name == null){
            throw new IllegalArgumentException("name is null!");
        }
        if(name.length() == 0){
            throw new IllegalArgumentException("name not long enough!");
        }
        this.name = name;
    }
    public String getName(){
        return name;
    }
    public void addStudent(Student student) throws ClassException{
        if(student == null){
            throw new NullPointerException("null student!");
        }
        if(students.contains(student)){
            throw new ClassException("student is already in the class!");
        }
        students.add(student);
    }
    public void removeStudent(Student student) throws ClassException{
        if(!(students.contains(student))){
            throw new ClassException("student not in the class!");
        }
        students.remove(student);
    }
    public int getClassAbsence(){
        int totalAbsence = 0;
        for(Student s : students){
            totalAbsence += s.getAbsences();
        }
        return totalAbsence;
    }
    public Set<Student> getAllStudents(){
        return students;
    }
    public Set<Student> getStudentsWithAbsence(){
        Set<Student> absenceStudents = new HashSet<Student>();
        for(Student s : students){
            if(s.getAbsences() > 0){
                absenceStudents.add(s);
            }
        }
        return absenceStudents;
    }
    //!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!upg
    public Set<Student> getStudentsWithoutAbsence(){
        Set<Student> symmetricDiff = new HashSet<Student>(getAllStudents());
        symmetricDiff.addAll(getAllStudents());
        // symmetricDiff now contains the union
        Set<Student> tmp = new HashSet<Student>(getStudentsWithAbsence());
        tmp.retainAll(getStudentsWithAbsence());
        // tmp now contains the intersection
        symmetricDiff.removeAll(tmp);
        // union minus intersection equals symmetric-difference
        /*
        Set<Student> absenceStudents = new HashSet<Student>();
        for(Student s : students){
            if(s.getAbsences() == 0){
                absenceStudents.add(s);
            }
        }
        return absenceStudents;
        */
        return symmetricDiff;
    }
    public Set<Student> removeStudents(String name){
        Set<Student> removedStudents = new HashSet<Student>();
        try{
            for(Student s : students){

                if(s.getName() == name){
                    removedStudents.add(s);
                    removeStudent(s);
                }
            }
        }
        catch(ClassException ex){

        }
        return removedStudents;
    }




}