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/*******************************************************************************
 * Copyright (c) 2010 itemis AG (http://www.itemis.eu) 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
 *******************************************************************************/
package org.eclipse.xtext.resource;

import java.util.List;

import org.eclipse.emf.ecore.EObject;
import org.eclipse.emf.ecore.EReference;
import org.eclipse.xtext.AbstractRule;
import org.eclipse.xtext.CrossReference;
import org.eclipse.xtext.EcoreUtil2;
import org.eclipse.xtext.GrammarUtil;
import org.eclipse.xtext.nodemodel.ILeafNode;
import org.eclipse.xtext.nodemodel.INode;
import org.eclipse.xtext.nodemodel.util.NodeModelUtils;
import org.eclipse.xtext.parser.IParseResult;
import org.eclipse.xtext.util.ITextRegion;
import org.eclipse.xtext.util.TextRegion;

/**
 * @author Jan Koehnlein - Initial contribution and API
 * @author Holger Schill
 */
public class EObjectAtOffsetHelper {

	/**
	 * @return the declared or the referenced element next to the offset
	 */
	public EObject resolveElementAt(XtextResource resource, int offset) {
		return internalResolveElementAt(resource, offset, false);
	}

	/**
	 * @return the declared element next to the offset
	 * @since 2.3
	 */
	public EObject resolveContainedElementAt(XtextResource resource, int offset) {
		return internalResolveElementAt(resource, offset, true);
	}
	
	/**
	 * @return the cross referenced EObject under, right or left to the cursor (in that order) or
	 *         null if there is no cross referenced object next to the offset.
	 */
	public EObject resolveCrossReferencedElementAt(XtextResource resource, int offset) {
		INode node = getCrossReferenceNode(resource, new TextRegion(offset, 0));
		if (node != null)
			return getCrossReferencedElement(node);
		return null;
	}
	
	/**
	 * @since 2.1
	 */
	public INode getCrossReferenceNode(XtextResource resource, ITextRegion region) {
		IParseResult parseResult = resource.getParseResult();
		if (parseResult != null) {
			ILeafNode leaf = NodeModelUtils.findLeafNodeAtOffset(parseResult.getRootNode(), region.getOffset());
			INode crossRefNode = findCrossReferenceNode(leaf);
			// if not a cross reference position and the cursor is at the beginning of a node try the previous one.
			if (crossRefNode == null && leaf != null && region.getLength()==0 && leaf.getOffset() == region.getOffset()) {
				leaf = NodeModelUtils.findLeafNodeAtOffset(parseResult.getRootNode(), region.getOffset() - 1);
				return findCrossReferenceNode(leaf);
			} else if (crossRefNode != null && crossRefNode.getOffset()+crossRefNode.getLength() >= region.getOffset() + region.getLength()) {
				return crossRefNode;
			}
		}
		return null;
	}
	
	/**
	 * @param node a node with an associated {@link CrossReference} grammar element.
	 * @return the {@link EObject} referenced by this node
	 * @since 2.1
	 */
	public EObject getCrossReferencedElement(INode node) {
		if (!(node.getGrammarElement() instanceof CrossReference))
			throw new IllegalArgumentException("Passed node not a cross reference node.");
		return resolveCrossReferencedElement(node);
	}

	/**
	 * @param node a node (possibly null)
	 * @return if the given node is part of a cross reference this method returns the node pointing to the
	 *         {@link CrossReference} null if the passed node was a null reference or if the passed node is
	 *         not part of a cross reference.
	 * @since 2.1
	 */
	protected INode findCrossReferenceNode(INode node) {
		if (node == null)
			return null;
		if (node.getGrammarElement() instanceof CrossReference)
			return node;
		while (node.getGrammarElement() != null && isElementOfDatatypeRule(node.getGrammarElement())) {
			node = node.getParent();
			if (node.getGrammarElement() instanceof CrossReference)
				return node;
		}
		return null;
	}

	/**
	 * @since 2.1
	 */
	protected boolean isElementOfDatatypeRule(final EObject grammarElement) {
		final AbstractRule rule = EcoreUtil2.getContainerOfType(grammarElement, AbstractRule.class);
		return GrammarUtil.isDatatypeRule(rule);
	}

	protected EObject internalResolveElementAt(XtextResource resource, int offset, boolean containment) {
		if(!containment) {
			EObject crossRef = resolveCrossReferencedElementAt(resource, offset);
			if (crossRef != null)
				return crossRef;
		}
		IParseResult parseResult = resource.getParseResult();
		if (parseResult != null) {
			ILeafNode leaf = NodeModelUtils.findLeafNodeAtOffset(parseResult.getRootNode(), offset);
			if (leaf != null && leaf.isHidden() && leaf.getOffset() == offset) {
				leaf = NodeModelUtils.findLeafNodeAtOffset(parseResult.getRootNode(), offset - 1);
			}
			if (leaf != null) {
				return NodeModelUtils.findActualSemanticObjectFor(leaf);
			}
		}
		return null;
	}

	protected EObject resolveCrossReferencedElement(INode node) {
		EObject referenceOwner = NodeModelUtils.findActualSemanticObjectFor(node);
		if (referenceOwner != null) {
			EReference crossReference = GrammarUtil.getReference((CrossReference) node.getGrammarElement(),
					referenceOwner.eClass());
			if (!crossReference.isMany()) {
				return (EObject) referenceOwner.eGet(crossReference);
			} else {
				List listValue = (List) referenceOwner.eGet(crossReference);
				List nodesForFeature = NodeModelUtils.findNodesForFeature(referenceOwner, crossReference);
				int currentIndex = 0;
				for (INode nodeForFeature : nodesForFeature) {
					if (currentIndex >= listValue.size())
						return null;
					if (nodeForFeature.getTotalOffset() <= node.getTotalOffset()
							&& nodeForFeature.getTotalEndOffset() >= node.getTotalEndOffset())
						return (EObject) listValue.get(currentIndex);
					currentIndex++;
				}
			}
		}
		return null;
	}

}