/* 
 * Copyright (c) 2008 Stiftung Deutsches Elektronen-Synchrotron, 
 * Member of the Helmholtz Association, (DESY), HAMBURG, GERMANY.
 *
 * THIS SOFTWARE IS PROVIDED UNDER THIS LICENSE ON AN "../AS IS" BASIS. 
 * WITHOUT WARRANTY OF ANY KIND, EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED 
 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR PARTICULAR PURPOSE AND 
 * NON-INFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE 
 * FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR 
 * THE USE OR OTHER DEALINGS IN THE SOFTWARE. SHOULD THE SOFTWARE PROVE DEFECTIVE 
 * IN ANY RESPECT, THE USER ASSUMES THE COST OF ANY NECESSARY SERVICING, REPAIR OR 
 * CORRECTION. THIS DISCLAIMER OF WARRANTY CONSTITUTES AN ESSENTIAL PART OF THIS LICENSE. 
 * NO USE OF ANY SOFTWARE IS AUTHORIZED HEREUNDER EXCEPT UNDER THIS DISCLAIMER.
 * DESY HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, 
 * OR MODIFICATIONS.
 * THE FULL LICENSE SPECIFYING FOR THE SOFTWARE THE REDISTRIBUTION, MODIFICATION, 
 * USAGE AND OTHER RIGHTS AND OBLIGATIONS IS INCLUDED WITH THE DISTRIBUTION OF THIS 
 * PROJECT IN THE FILE LICENSE.HTML. IF THE LICENSE IS NOT INCLUDED YOU MAY FIND A COPY 
 * AT HTTP://WWW.DESY.DE/LEGAL/LICENSE.HTM
 */
 package org.csstudio.sds.ui.internal.layers;

import org.csstudio.sds.internal.model.Layer;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.jface.resource.JFaceResources;
import org.eclipse.jface.util.LocalSelectionTransfer;
import org.eclipse.jface.util.Policy;
import org.eclipse.swt.dnd.ByteArrayTransfer;
import org.eclipse.swt.dnd.TransferData;

/**
 * Transfer handler for layers. Implements a pattern similar to
 * {@link LocalSelectionTransfer}.
 * 
 * @author swende
 * 
 */
final class LayerTransfer extends ByteArrayTransfer {

	/**
	 * Type name.
	 */
	private static final String TYPE_NAME = "sds.layertransfer";

	/**
	 * Type identifier.
	 */
	private static final int TYPE_ID = registerType(TYPE_NAME);

	/**
	 * Singleton instance.
	 */
	private static LayerTransfer _instance;

	/**
	 * Currently selected layer.
	 */
	private Layer _selectedLayer;

	/**
	 * Private constructor (singleton pattern).
	 */
	private LayerTransfer() {

	}

	/**
	 * Returns the singleton instance.
	 * 
	 * @return the singleton instance
	 */
	public static LayerTransfer getInstance() {
		if (_instance == null) {
			_instance = new LayerTransfer();
		}
		return _instance;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	protected String[] getTypeNames() {
		return new String[] { TYPE_NAME };
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	protected int[] getTypeIds() {
		return new int[] { TYPE_ID };
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void javaToNative(final Object object,
			final TransferData transferData) {
		byte[] check = TYPE_NAME.getBytes();
		super.javaToNative(check, transferData);
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public Object nativeToJava(final TransferData transferData) {
		Object result = super.nativeToJava(transferData);
		if (isInvalidNativeType(result)) {
			Policy
					.getLog()
					.log(
							new Status(
									IStatus.ERROR,
									Policy.JFACE,
									IStatus.ERROR,
									JFaceResources
											.getString("LocalSelectionTransfer.errorMessage"), null)); //$NON-NLS-1$
		}
		return _selectedLayer;
	}

	/**
	 * Tests whether native drop data matches this transfer type.
	 * 
	 * @param result
	 *            result of converting the native drop data to Java
	 * @return true if the native drop data does not match this transfer type.
	 *         false otherwise.
	 */
	private boolean isInvalidNativeType(final Object result) {
		return !(result instanceof byte[])
				|| !TYPE_NAME.equals(new String((byte[]) result));
	}

	/**
	 * Sets the transfer data for local use.
	 * 
	 * @param selectedLayer
	 *            the transfered layer
	 */
	public void setSelectedLayer(final Layer selectedLayer) {
		_selectedLayer = selectedLayer;
	}
}