NullElementPointer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE
 * file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file
 * to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the
 * License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */
/*******************************************************************************
 * Copyright (c) 2010 BestSolution.at 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: Tom Schindl <tom.schindl@bestsolution.at> - adjustment to EObject
 ******************************************************************************/
package org.eclipse.e4.emf.internal.xpath;

import org.apache.commons.jxpath.JXPathContext;
import org.apache.commons.jxpath.ri.QName;
import org.apache.commons.jxpath.ri.model.NodePointer;

/**
 * Used when there is a need to construct a Pointer for a collection element that does not exist. For example, if the
 * path is "foo[3]", but the collection "foo" only has one element or is empty or is null, the NullElementPointer can be
 * used to capture this situation without putting a regular NodePointer into an invalid state. Just create a
 * NullElementPointer with index 2 (= 3 - 1) and a "foo" pointer as the parent.
 * 
 * 
 */
public class NullElementPointer extends CollectionPointer {

	private static final long serialVersionUID = 8714236818791036721L;

	/**
	 * Create a new NullElementPointer.
	 * 
	 * @param parent
	 *            parent pointer
	 * @param index
	 *            int
	 */
	public NullElementPointer(NodePointer parent, int index) {
		super(parent, (Object) null);
		this.index = index;
	}

	@Override
	public QName getName() {
		return null;
	}

	@Override
	public Object getBaseValue() {
		return null;
	}

	@Override
	public Object getImmediateNode() {
		return null;
	}

	@Override
	public boolean isLeaf() {
		return true;
	}

	@Override
	public boolean isCollection() {
		return false;
	}

	/**
	 * Get the property pointer for this.
	 * 
	 * @return PropertyPointer
	 */
	public EStructuralFeaturePointer getPropertyPointer() {
		return new NullEStructuralFeaturePointer(this);
	}

	@Override
	public NodePointer getValuePointer() {
		return new NullPointer(this, getName());
	}

	@Override
	public void setValue(Object value) {
		throw new UnsupportedOperationException("Collection element does not exist: " + this);
	}

	@Override
	public boolean isActual() {
		return false;
	}

	@Override
	public boolean isContainer() {
		return true;
	}

	@Override
	public NodePointer createPath(JXPathContext context) {
		return parent.createChild(context, null, index);
	}

	@Override
	public NodePointer createPath(JXPathContext context, Object value) {
		return parent.createChild(context, null, index, value);
	}

	@Override
	public int hashCode() {
		return getImmediateParentPointer().hashCode() + index;
	}

	@Override
	public boolean equals(Object object) {
		if (object == this) {
			return true;
		}

		if (!(object instanceof NullElementPointer)) {
			return false;
		}

		NullElementPointer other = (NullElementPointer) object;
		return getImmediateParentPointer() == other.getImmediateParentPointer() && index == other.index;
	}

	@Override
	public int getLength() {
		return 0;
	}

	@Override
	public String asPath() {
		StringBuffer buffer = new StringBuffer();
		NodePointer parent = getImmediateParentPointer();
		if (parent != null) {
			buffer.append(parent.asPath());
		}
		if (index != WHOLE_COLLECTION) {
			// Address the list[1][2] case
			if (parent != null && parent.getIndex() != WHOLE_COLLECTION) {
				buffer.append("/.");
			}
			else if (parent != null && parent.getImmediateParentPointer() != null
					&& parent.getImmediateParentPointer().getIndex() != WHOLE_COLLECTION) {
				buffer.append("/.");
			}
			buffer.append("[").append(index + 1).append(']');
		}

		return buffer.toString();
	}
}