/*******************************************************************************
 * Copyright (c) 2000, 2015 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.ui.part;

import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtension;
import org.eclipse.core.runtime.IExtensionPoint;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.Platform;
import org.eclipse.jface.viewers.StructuredViewer;
import org.eclipse.jface.viewers.ViewerDropAdapter;
import org.eclipse.swt.dnd.DND;
import org.eclipse.swt.dnd.DropTargetEvent;
import org.eclipse.swt.dnd.TransferData;
import org.eclipse.ui.PlatformUI;
import org.eclipse.ui.internal.WorkbenchPlugin;
import org.eclipse.ui.internal.registry.IWorkbenchRegistryConstants;

/**
 * Adapter for adding handling of the <code>PluginTransfer</code> drag and drop
 * transfer type to a drop action.
 * <p>
 * This class may be instantiated or subclassed.
 * </p>
 */
public class PluginDropAdapter extends ViewerDropAdapter {
	/**
	 * The extension point attribute that defines the drop action class.
	 */
	public static final String ATT_CLASS = "class";//$NON-NLS-1$

	/**
	 * The current transfer data, or <code>null</code> if none.
	 */
	private TransferData currentTransfer;

	/**
	 * Creates a plug-in drop adapter for the given viewer.
	 *
	 * @param viewer the viewer
	 */
	public PluginDropAdapter(StructuredViewer viewer) {
		super(viewer);
	}

	@Override
	public void drop(DropTargetEvent event) {
		try {
			if (PluginTransfer.getInstance().isSupportedType(event.currentDataType)) {
				PluginTransferData pluginData = (PluginTransferData) event.data;
				IDropActionDelegate delegate = getPluginAdapter(pluginData);
				if (!delegate.run(pluginData.getData(), getCurrentTarget())) {
					event.detail = DND.DROP_NONE;
				}
			} else {
				super.drop(event);
			}
		} catch (CoreException e) {
			WorkbenchPlugin.log("Drop Failed", e.getStatus());//$NON-NLS-1$
		}
	}

	/**
	 * Returns the current transfer.
	 */
	protected TransferData getCurrentTransfer() {
		return currentTransfer;
	}

	/**
	 * Loads the class that will perform the action associated with the given drop
	 * data.
	 *
	 * @param data the drop data
	 * @return the viewer drop adapter
	 */
	protected static IDropActionDelegate getPluginAdapter(PluginTransferData data) throws CoreException {

		IExtensionRegistry registry = Platform.getExtensionRegistry();
		String adapterName = data.getExtensionId();
		IExtensionPoint xpt = registry.getExtensionPoint(PlatformUI.PLUGIN_ID,
				IWorkbenchRegistryConstants.PL_DROP_ACTIONS);
		IExtension[] extensions = xpt.getExtensions();
		for (IExtension extension : extensions) {
			IConfigurationElement[] configs = extension.getConfigurationElements();
			if (configs != null && configs.length > 0) {
				for (IConfigurationElement config : configs) {
					String id = config.getAttribute("id");//$NON-NLS-1$
					if (id != null && id.equals(adapterName)) {
						return (IDropActionDelegate) WorkbenchPlugin.createExtension(config, ATT_CLASS);
					}
				}
			}
		}
		return null;
	}

	/**
	 * @see ViewerDropAdapter#performDrop
	 */
	@Override
	public boolean performDrop(Object data) {
		// should never be called, since we override the drop() method.
		return false;
	}

	/**
	 * The <code>PluginDropAdapter</code> implementation of this
	 * <code>ViewerDropAdapter</code> method is used to notify the action that some
	 * aspect of the drop operation has changed. Subclasses may override.
	 */
	@Override
	public boolean validateDrop(Object target, int operation, TransferData transferType) {
		currentTransfer = transferType;
		if (currentTransfer != null && PluginTransfer.getInstance().isSupportedType(currentTransfer)) {
			// plugin cannot be loaded without the plugin data
			return true;
		}
		return false;
	}
}
