/*
 * QueuedWRVectorModel.java, (c) Raimond Reichert July 1999
 */
package mldemo;

import java.util.*;
import java.lang.ref.*;

/**
  * Implements <code>VectorModel</code> with weak references, ie, using
  * a <code>Vector</code> to hold <code>WeakReference</code>s which in turn
  * hold the references to the <code>VectorModel.Listener</code>s.
  *
  * <p><code>ThreadedWRVectorModel</code> registers the
  * <code>WeakReference</code>s with a <code>ReferenceQueue</code>.
  * Before firing an event, the <code>cleanUp</code> method is called. This method
  * polls the queue. If there is any enqueued reference, then the reference
  * is removed from the <code>listeners</code> list.
  *
  * @author Raimond Reichert
  */
public class QueuedWRVectorModel implements VectorModel {

  private Vector vector;
  private Vector listeners;
  private ReferenceQueue queue;

  public QueuedWRVectorModel() {
    vector    = new Vector();
    listeners = new Vector();
    queue     = new ReferenceQueue();
  } // QueuedWRVectorModel //

  public void addElement (Object object) {
    vector.addElement (object);
    fireElementAdded (object);
  } // addElement //

  public void removeElement (Object object) {
    vector.removeElement (object);
    fireElementRemoved (object);
  } // removeElement //

  public Object elementAt (int index) {
    return vector.elementAt (index);
  } // elementAt //

  public int size() {
    return vector.size();
  } // size //

  public void addListener (VectorModel.Listener l) {
    WeakReference wr = new WeakReference (l, queue);
    listeners.addElement (wr);
  } // addListener //

  /**
    * Polls the reference queue, and removes all references on it from
    * the listeners vector.
    */
  public void cleanUp() {
    WeakReference wr = (WeakReference)queue.poll();
    while (wr != null) {
      listeners.removeElement (wr);
      System.out.println ("QueuedWRVectorModel: removed weak reference");
      wr = (WeakReference)queue.poll();
    }
  } // cleanUp //

  public void removeListener (VectorModel.Listener l) {
    int size = listeners.size();
    int i = 0;
    while (i < size) {
      WeakReference wr = (WeakReference)listeners.elementAt(i);
      VectorModel.Listener vml = (VectorModel.Listener)wr.get();
      if (vml == l) {
        listeners.removeElement (wr);
        size--;
      }
      else
        i++;
    }
  } // removeListener //

  protected void fireElementAdded (Object object) {
    cleanUp();

    VectorModel.Event e = null;
    int size = listeners.size();
    int i = 0;

    while (i < size) {
      WeakReference wr = (WeakReference)listeners.elementAt(i);
      VectorModel.Listener vml = (VectorModel.Listener)wr.get();
      if (vml != null) {
        if (e == null) // lazily create event
          e = new VectorModel.Event (this, object);
        vml.elementAdded (e);
        i++;
      }
    }
  } // fireElementAdded //

  protected void fireElementRemoved (Object object) {
    cleanUp();

    VectorModel.Event e = null;
    int size = listeners.size();
    int i = 0;

    while (i < size) {
      WeakReference wr = (WeakReference)listeners.elementAt(i);
      VectorModel.Listener vml = (VectorModel.Listener)wr.get();
      if (vml != null) {
        if (e == null) // lazily create event
          e = new VectorModel.Event (this, object);
        vml.elementRemoved (e);
        i++;
      }
    }
  } // fireElementRemoved //

} // QueuedWRVectorModel //