/*******************************************************************************
 * Copyright (c) 2004, 2005 IBM Corporation and others. All rights reserved. This program and the
 * accompanying materials are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html Contributors: IBM Corporation - Initial API and
 * implementation Jens Lukowski/Innoopract - initial renaming/restructuring
 *******************************************************************************/
package org.eclipse.wst.common.ui.internal.dnd;

import org.eclipse.swt.dnd.ByteArrayTransfer;
import org.eclipse.swt.dnd.TransferData;

/**
 * This derived implementation of a byte array transfer short circuits the transfer process so that
 * a local transfer does not serialize the object and hence can and will return the original object,
 * not just a clone. You only really need ever know about {@link #getInstance
 * ObjectTransfer.getInstance()}, so that you can include it in when adding drag support to a
 * viewer. See {@link EditingDomainViewerDropAdapter} and {@link ViewerDragAdapter} for more
 * details.
 * <p>
 * As an addded guard, the time is recorded and serialized in javaToNative to that navive to java
 * can ensure that it's returns the value that was really to have been transferred.
 */
public class ObjectTransfer extends ByteArrayTransfer {
  /**
   * This is the register transfer type name.
   */
  protected static final String TYPE_NAME = "local-transfer-format";

  /**
   * This is the ID that is registered to the name.
   */
  protected static final int TYPE_ID = registerType(TYPE_NAME);

  /**
   * This is initialized and returned by {@link #getInstance}.
   */
  protected static ObjectTransfer instance;

  /**
   * This returns the one instance of this transfer agent.
   */
  public static ObjectTransfer getInstance() {
    if (instance == null) {
      instance = new ObjectTransfer();
    }

    return instance;
  }

  /**
   * This records the time at which the transfer data was recorded.
   */
  protected long startTime;

  /**
   * This records the data being transferred.
   */
  protected Object object;

  /**
   * This creates an instance; typically you get one from {@link #getInstance}.
   */
  protected ObjectTransfer() {
  }

  /**
   * This returns the transfer ids that this agent supports.
   */
  protected int[] getTypeIds() {
    return new int[] {TYPE_ID};
  }

  /**
   * This returns the transfer names that this agent supports.
   */
  public String[] getTypeNames() {
    return new String[] {TYPE_NAME};
  }

  /**
   * This records the object and current time and encodes only the current time into the transfer
   * data.
   */
  public void javaToNative(Object object, TransferData transferData) {
    startTime = System.currentTimeMillis();
    this.object = object;
    if (transferData != null) {
      super.javaToNative(String.valueOf(startTime).getBytes(), transferData);
    }
  }

  /**
   * This decodes the time of the transfer and returns the recorded the object if the recorded time
   * and the decoded time match.
   */
  public Object nativeToJava(TransferData transferData) {
    long startTime = Long.valueOf(new String((byte[]) super.nativeToJava(transferData))).longValue();
    return this.startTime == startTime ? object : null;
  }
}