// A user interface used once yearly updates the set of Module objects in the
// system and updates the lecturer field of each. Name is only set on object
// creation. Description may be updated by the lecturer.
import java.util.*;

public class Module {
    public Module() {}

   public Module (String aname, String adescription, Lecturer alecturer) {
       name = aname;
       description = adescription;
       lecturer = alecturer;
   }

   public void setLecturer (Lecturer l) {
       lecturer = l;
   }

// Assumed process: a lecturer who wants to update the description must check
// it out by a certain date. If they do not do so, it is assumed that no 
// changes are needed.
   public String checkOutDescription (Lecturer l) {
       String description = "";
       if (l == lecturer) {
	   descriptionUpToDate = false;
       } else {
	   System.out.println 
	       ("Sorry, only the lecturer can upate the module description");
       }
       return description; 
   }

   public void checkInDescription (Lecturer l, String newDescription) {
       if (l == lecturer) {
	   description = newDescription;
	   descriptionUpToDate = true;
       } else {
	   System.out.println
	       ("Sorry, only the lecturer can upate the module description");
       }
   }
        
   public boolean isUpToDate () {return descriptionUpToDate;}

    // Hackish thing just to make sure HashSet with Modules in doesn't get 
    // upset when their lecturer fields change. Should be futureproofed.
    public boolean equals (Object o) {
	try{
	if (o.getClass() == Class.forName("Module")) {
	    return ((Module)o).name == name;
	} else return false;
	} catch (java.lang.ClassNotFoundException e) {
	    //Panic: you can see this can't happen.
	    return false;
	}
    }

    public void registerStudent (Student s) {
	students.put(s.name, s);
    }

    public void deregisterStudent (Student s) {
	students.remove(s.name);
    }

    public String makeStudentList() {
	Iterator i = students.keySet().iterator();
	String str = "Class list for module "+name+"\n";
	while (i.hasNext()) {
	    Student s = (Student)i.next();
	    str = str + s.name + "\n";
	}
	return str;
    }

    String name;
    String description;
    Lecturer lecturer;
    private boolean descriptionUpToDate = true;
    private HashMap students = new HashMap();
}