module CourseDB;
export CourseDB;

  object CourseDB
    components: CourseEntry*;
    operations: AddEntry, RemoveEntry, ChangeEntry;
    description: (*
        The CourseDB is the database for each schedule.  It contains all
        of the avaiable courses.
    *);
  end;

  object CourseEntry
    components: coursedepartment:CourseDepartment and coursenumber:CourseNumber and coursename:CourseName and coursetype:CourseType and 
    coursemaxenroll:CourseMaxEnroll and courselabpairing:CourseLabPairing and coursewtus:CourseWTUs and courseequipment:CourseEquipment and
    coursedescription:CourseDescription;
  	 description: (*
            A Course entry contains a department, course number, course name,
            type, maximum enrollment, lab pairing, WTUs, required equipment, 
            and a description
  	 *);
  end;
  
  object CourseName = string;
  object CourseDepartment = string;
  object CourseType = Lecture or Lab;
  object Lecture = string and boolean;
  object Lab = string;
  object CourseMaxEnroll = integer;
  object CourseWTUs = integer;
  object CourseEquipment = string;
  object CourseDescription = string;
  object CourseNumber = integer;
  object CourseLabPairing = boolean;

  operation AddEntry
    inputs: cdb:CourseDB, ce:CourseEntry;
    outputs: cdb':CourseDB;
    description: (* This operation adds a course entry to the course 
    database.*);

    precondition:
        (*
         * There is no user record in the input CourseDB with the same Department and Course Number as the
         * record to be added.  The Department, Course Number, and WTUs must not be empty.
         *)
        (not (exists (ce' in cdb) ce'.coursedepartment = ce.coursedepartment and ce'.coursenumber = ce.coursenumber))
	and
	ce.coursedepartment != nil and ce.coursenumber != nil and ce.coursewtus != nil;

    postcondition:
        (*
         * There is no user record in the input CourseDB with the same Department and Course Number as the
         * record to be added.
         *
         * A course entry is in the output db if and only if it is the new
         * record to be added or it is in the input db.
         *)
        forall (ce':CourseEntry)
           (ce' in cdb') iff ((ce' = ce) or (ce' in cdb));

  end;

  operation RemoveEntry
    inputs: cdb:CourseDB, ce:CourseEntry;
    outputs: cdb':CourseDB;
    description: (* This operation removes a course entry from the course 
    database by department and number.*);
    precondition: (* The entry is in the database*)
    (ce in cdb);
    postcondition: (* The entry is not in the database, but all other entries are still there *)
    (forall (ce':CourseEntry)
            (ce' in cdb') iff ((ce' != ce) and (ce' in cdb)));

  end;

  operation ChangeEntry
    inputs: cdb:CourseDB, oldCE:CourseEntry, newCE:CourseEntry;
    outputs: cdb':CourseDB;
    description: (* This operation removes the old entry and adds a new entry to the database.*);

    precondition: (* Old entry must exist in the database, don't care if the new entry is the same as the old one.*)
    (oldCE in cdb) and newCE.coursedepartment != nil and newCE.coursenumber != nil and newCE.coursewtus != nil;

    postcondition:
                 (*The old entry does not exist and the new entry does exist*)
    (newCE in cdb') and not(oldCE in cdb');
  end;
end CourseDB;