/***********************************************************************
 * Copyright (c) 2008 by SAP AG, Walldorf. 
 * 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:
 *     SAP AG - initial API and implementation
 ***********************************************************************/
package org.eclipse.jst.jee.model.internal.common;

import java.util.ArrayList;
import java.util.Collection;

import org.eclipse.core.resources.IProject;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IPath;
import org.eclipse.core.runtime.ISafeRunnable;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.SafeRunner;
import org.eclipse.emf.ecore.EObject;
import org.eclipse.emf.ecore.resource.Resource;
import org.eclipse.emf.ecore.resource.impl.ResourceImpl;
import org.eclipse.jst.j2ee.model.IModelProvider;
import org.eclipse.jst.j2ee.model.IModelProviderEvent;
import org.eclipse.jst.j2ee.model.IModelProviderListener;
import org.eclipse.jst.jee.JEEPlugin;

/**
 * A base class for model providers providing a merged view between two
 * different model providers. The instance will be called "mergedModelProvider"
 * where the two composed providers will be called "internalProviders"
 * 
 * This class introduces the notation of a disposed state. {@link #dispose()} is
 * used to dispose the model provider. {@link #isDisposed()} is used to get the
 * state of the provider. If the method {@link #getModelObject()} is called for
 * a model provider in a disposed state, the provider should try to move to a
 * non disposed state and return a correct model object.
 * {@link #getModelObject()} is loading the model. Specific implementations may
 * throw exceptions so calling {@link #getModelObject()} on a disposed provider
 * does not guarantee that calling {@link #isDisposed()} after that will return
 * <code>false</code>.
 * 
 * <p>
 * Subclasses may enable/disable notifications from internalProviders with the
 * methods {@link #enableInternalNotifications()} and
 * {@link #disableInternalNotifications()}.
 * </p>
 * 
 * <p>
 * internalProviders are loaded with {@link #loadDeploymentDescriptorModel()}
 * and {@link #loadAnnotationModel(Object)}. This methods should be override to
 * provide specific model providers.
 * </p>
 * 
 * <p>
 * The mergedModelProvider is a listener to the internalProviders. After
 * disposing the instance of a mergedModelProvider it should no longer accept
 * notifications from the internalProviders. It should also properly "dispose"
 * the internalProviders if needed.
 * </p>
 * 
 * @author Kiril Mitov k.mitov@sap.com
 * 
 */
public abstract class AbstractMergedModelProvider<T> implements IModelProvider {

	protected IModelProvider ddProvider;

	protected IModelProvider annotationModelProvider;

	private class AnnotationModelListener implements IModelProviderListener {
		public void modelsChanged(IModelProviderEvent event) {
			if (disposeIfNeeded(event))
				return;
			AbstractMergedModelProvider.this.annotationModelChanged(event);
		}
	}

	private class XmlModelListener implements IModelProviderListener {
		public void modelsChanged(IModelProviderEvent event) {
			if (disposeIfNeeded(event))
				return;
			AbstractMergedModelProvider.this.xmlModelChanged(event);
		}
	}

	/**
	 * @param event
	 * @return true if the model provider is disposed.
	 */
	private boolean disposeIfNeeded(IModelProviderEvent event) {
		if (isDisposed() || mergedModel == null)
			return true;
		if (shouldDispose(event)) {
			dispose();
			notifyListeners(event);
			return true;
		}
		return false;
	}

	private Collection<IModelProviderListener> listeners;

	protected IProject project;

	private AnnotationModelListener annotationModelListener;
	private XmlModelListener xmlModelListener;

	protected T mergedModel;

	public AbstractMergedModelProvider(IProject project) {
		this.project = project;
	}

	public void addListener(IModelProviderListener listener) {
		getListeners().add(listener);
	}

	/**
	 * Returns the model merged from annotation and xml model. If the project is
	 * closed or does not exist the returns <code>null</code>
	 * 
	 * @see org.eclipse.jst.j2ee.model.IModelProvider#getModelObject()
	 */
	public Object getModelObject() {
		return getMergedModel();
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jst.j2ee.model.IModelProvider#modify(java.lang.Runnable,
	 * org.eclipse.core.runtime.IPath)
	 */
	public void modify(Runnable runnable, IPath modelPath) {
	}

	public void removeListener(IModelProviderListener listener) {
		getListeners().remove(listener);
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.eclipse.jst.j2ee.model.IModelProvider#validateEdit(org.eclipse.core
	 * .runtime.IPath, java.lang.Object)
	 */
	public IStatus validateEdit(IPath modelPath, Object context) {
		if (ddProvider == null)
			getModelObject();
		return ddProvider.validateEdit(modelPath, context);
	}

	/**
	 * Called when the annotationModel has changed. See also
	 * {@link #enableInternalNotifications()} and
	 * {@link #disableInternalNotifications()}
	 * 
	 * @param event
	 */
	protected abstract void annotationModelChanged(IModelProviderEvent event);

	/**
	 * Called when the xmlModel has changed. See also
	 * {@link #enableInternalNotifications()} and
	 * {@link #disableInternalNotifications()}
	 * 
	 * @param event
	 */
	protected abstract void xmlModelChanged(IModelProviderEvent event);

	/**
	 * Return a merged view of the two passed models.
	 * 
	 * @param ddModel
	 * @param annotationsModel
	 * @return
	 */
	protected abstract T merge(T ddModel, T annotationsModel);

	/**
	 * Load the annotation model in the context of the ddModel.
	 * 
	 * @param ddModel
	 * @return
	 * @throws CoreException
	 */
	protected abstract IModelProvider loadAnnotationModel(T ddModel) throws CoreException;

	/**
	 * @return
	 * @throws CoreException
	 */
	protected abstract IModelProvider loadDeploymentDescriptorModel() throws CoreException;

	protected Collection<IModelProviderListener> getListeners() {
		if (listeners == null)
			listeners = new ArrayList<IModelProviderListener>();
		return listeners;
	}

	protected T getMergedModel() {
		try {
			if (mergedModel == null)
				mergedModel = loadModel();
		} catch (CoreException e) {
			JEEPlugin.getDefault().getLog().log(e.getStatus());
			return null;
		}
		return mergedModel;
	}

	/**
	 * @return a merged view of the models from the internalProviders. This may
	 *         include loading the internalProviders.
	 * @throws CoreException
	 */
	protected T loadModel() throws CoreException {
		if (project.isAccessible() == false)
			throw new IllegalStateException("The project <" + project + "> is not accessible."); //$NON-NLS-1$//$NON-NLS-2$
		if (ddProvider == null)
			ddProvider = loadDeploymentDescriptorModel();
		if (ddProvider == null || ddProvider.getModelObject() == null)
			return null;
		if (annotationModelProvider == null)
			annotationModelProvider = loadAnnotationModel((T) ddProvider.getModelObject());
		if (annotationModelProvider == null || annotationModelProvider.getModelObject() == null)
			return null;
		T ddModel = (T) ddProvider.getModelObject();
		T annotationModel = (T) annotationModelProvider.getModelObject();
		mergedModel = createNewModelInstance();
		initMergedModelResource((EObject) ddModel);

		enableInternalNotifications();
		return merge(ddModel, annotationModel);
	}

	/**
	 * Creates a new instance of the model that will be used for mergedModel
	 * 
	 * @return
	 */
	protected abstract T createNewModelInstance();

	protected void initMergedModelResource(EObject ddModel) {
		Resource resourceDD = ddModel.eResource();
		Resource resourceMM = ((EObject) mergedModel).eResource();
		if (resourceDD != null && resourceMM == null) {
			ResourceImpl resRes = new ResourceImpl(resourceDD.getURI());
			resRes.getContents().add((EObject) mergedModel);
		}

	}

	/**
	 * The method is used for enabling notifications from the internalProviders.
	 * This will add the appropriate listener to the internalProviders so that
	 * {@link #annotationModelChanged(IModelProviderEvent)} and
	 * {@link #xmlModelChanged(IModelProviderEvent)} are called when needed.
	 */
	protected final void enableInternalNotifications() {
		xmlModelListener = new XmlModelListener();
		ddProvider.addListener(xmlModelListener);
		annotationModelListener = new AnnotationModelListener();
		annotationModelProvider.addListener(annotationModelListener);
	}

	/**
	 * Disable notifications from internalProviders. See also
	 * {@link #enableInternalNotifications()}
	 */
	protected final void disableInternalNotifications() {
		ddProvider.removeListener(xmlModelListener);
		annotationModelProvider.removeListener(annotationModelListener);
	}

	protected void notifyListeners(final IModelProviderEvent event) {
		event.setModel(this);
		event.setProject(project);
		final Collection<IModelProviderListener> listeners = getListeners();
		IModelProviderListener[] backup = listeners.toArray(new IModelProviderListener[listeners.size()]);
		for (final IModelProviderListener listener : backup) {
			SafeRunner.run(new ISafeRunnable() {
				public void handleException(Throwable exception) {
				}

				public void run() throws Exception {
					listener.modelsChanged(event);
				}
			});
		}
		backup = null;
	}

	protected boolean shouldDispose(IModelProviderEvent event) {
		return (event.getEventCode() == IModelProviderEvent.UNLOADED_RESOURCE);
	}

	/**
	 * Returns the dispose state of this model provider. When the provider is
	 * disposed it can not be used until getModelObject is called again.
	 * 
	 * Subclasses may override this method.
	 * 
	 * @return true if the model provider is to be treated as disposed
	 */
	public boolean isDisposed() {
		return (ddProvider == null && annotationModelProvider == null);
	}

	/**
	 * Dispose the model provider. If the provider is already disposed the
	 * method has no effect.
	 * 
	 * Subclasses may override this method.
	 * 
	 * @see #isDisposed()
	 */
	public void dispose() {
		if (isDisposed())
			return;
		disableInternalNotifications();
		ddProvider = null;
		annotationModelProvider = null;
		mergedModel = null;
	}

}