import org.datamanager.kernel.Simpleton;
import org.datamanager.kernel.Entity;
import org.datamanager.kernel.Pool;
import org.datamanager.constraint.Constraint;
import org.datamanager.constraint.ValueClassIsConstraint;
import org.datamanager.event.DataManagerEvent;
import org.datamanager.event.SetValueEvent;
import org.datamanager.exception.DataManagerException;
import org.datamanager.entityvalue.IntegerEntityValue;
import org.datamanager.entityvalue.StringEntityValue;

public class ExampleSimpleton extends Simpleton implements EventHandler
   {
   public void process()
      {
      try
         {
         //fetch the set of all entities in the default pool
         //and just die if there are only 0 or 1 entities
         Pool pool = Pool.getDefaultPool();
         Entity[] entityList = pool.search(Constraint.NONE);
         if (entityList.length < 2)
            return;

         Entity entity1 = entityList[0];
         Entity entity2 = entityList[1];

         //let me know whenever anyone changes entity1
         ValueClassIsConstraint eventConstraint =
            new ValueClassIsConstraint(SetValueEvent.class);
         entity1.subscribe(this, eventConstraint);

         //alter entity1's value
         //and make entity2 an attribute of entity1
         entity1.setValue(new IntegerEntityValue(5));
         entity1.attach(entity2);

         //create a new entity to hold a string
         //and link it in as an attribute of entity2
         Entity entity3 = Entity.create("my new entity");
         entity3.setValue(new StringEntityValue("my marker"));
         entity2.attach(entity3);

         //note that entity3 can now be found by searches on the pool
         //even though we haven't added it to the pool

         //stop subscribing to entity1
         entity1.unsubscribe(this);
         }
      catch (DataManagerException exception)
         {
         //do something when an exception happens
         System.out.println(exception + " happened in kernel");

         /*
         Currently the kernel supports only one catchall
         exception class, DataManagerException, a subclass of
         java.lang.Exception,
         and it (so far) carries no new methods of its own.
         For now, simply put all your code in one try-catch block
         and catch all DataManagerExceptions.
         */
         }
      }

   public void handle(DataManagerEvent event)
      {
      //someone changed entity1's value...
      System.out.println(((Entity) event.getSource()).getName() +
         " sent me an event");
      }
   }