package admin;
import java.util.Collection;

/**
 * GroupDB is the repository of user group information.
 */
public abstract class GroupDB {

    /**
     * The collection of group data records.
     */
    Collection<GroupRecord> data;

    /**
     * Reference to GroupDB needed for change and delete methods.
     */
    UserDB userDB;

    /**
      * Add the given GroupRecord to the given GroupDB.  The name of the given
      * group must not be the same as a group already in the GroupDB.  All
      * group members must be registered users.  The leader(s) of the group
      * must be members of it.
      */
    abstract void add(GroupRecord gr);

    /**
     * Delete the given group record from the given GroupDB.  The given record
     * must already be in the input db.  Typically the user runs the FindGroup
     * operation prior to Delete to locate an existing record to delete.
     */
    abstract void delete(GroupRecord gr);

    /**
     * Change the given old GroupRecord to the given new record.  The old and
     * new records must not be the same.  The old record must already be in
     * the input db.  The new record must meet the same conditions as for the
     * input to the AddGroup operation.  Typically the user runs the FindGroup
     * operation prior to Change to locate an existing record to be changed.
     */
    abstract void change(GroupRecord old_gr, GroupRecord new_gr);

    /**
     * Find a group by unique name.
     */
    abstract GroupRecord findById(String id);

}