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/*******************************************************************************
 * Copyright (c) 2008 itemis AG (http://www.itemis.eu) and others.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * SPDX-License-Identifier: EPL-2.0
 *******************************************************************************/
package org.eclipse.xtext.util;

import org.eclipse.emf.common.notify.Adapter;
import org.eclipse.emf.common.notify.Notification;
import org.eclipse.emf.common.notify.Notifier;
import org.eclipse.emf.ecore.EAttribute;
import org.eclipse.emf.ecore.EClass;
import org.eclipse.emf.ecore.ENamedElement;
import org.eclipse.emf.ecore.EObject;
import org.eclipse.emf.ecore.EStructuralFeature;

import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.collect.Iterables;

/**
 * @author Sebastian Zarnekow - Initial contribution and API
 * TODO measure whether this thing is worth the effort
 */
public class SimpleAttributeResolver implements Function{
	
	public final static SimpleAttributeResolver NAME_RESOLVER = newResolver(String.class, "name");

	private final SimpleCache attributeCache;

	private final SimpleCache valueCache;

	private final String attributeName;

	private final Adapter discardingAdapter;

	public static  SimpleAttributeResolver newResolver(final Class type, final String attributeName) {
		return new SimpleAttributeResolver(type, attributeName);
	}

	public EAttribute getAttribute(final EObject object) {
		return attributeCache.get(object.eClass());
	}

	protected SimpleAttributeResolver(final Class type, final String attributeName) {
		this.attributeName = attributeName;
		this.discardingAdapter = new DiscardingAdapter(this);
		attributeCache = new SimpleCache(new Function() {
			@Override
			public EAttribute apply(EClass param) {
				final EStructuralFeature structuralFeature = param.getEStructuralFeature(attributeName);
				if (structuralFeature != null && structuralFeature instanceof EAttribute && !structuralFeature.isMany()) {
					if (type.isAssignableFrom(structuralFeature.getEType().getInstanceClass())) {
						return (EAttribute) structuralFeature;
					}
				}
				return null;
			}
		});
		valueCache = new SimpleCache(new Function() {
			@Override
			@SuppressWarnings("unchecked")
			public T apply(EObject param) {
				final EStructuralFeature feature = attributeCache.get(param.eClass());
				if (feature != null) {
					param.eAdapters().add(discardingAdapter);
				}
				return feature != null ? ((T) param.eGet(feature)) : null;
			}
		});
	}

	public T getValue(final K object) {
		return object != null ? valueCache.get(object) : null;
	}

	public Iterable getMatches(final Iterable candidates, final T value) {
		return Iterables.filter(candidates, new Predicate() {
			@Override
			public boolean apply(K param) {
				final T candidateValue = getValue(param);
				return value.equals(candidateValue);
			}
		});
	}

	private static class DiscardingAdapter implements Adapter {

		private SimpleAttributeResolver resolver;

		private DiscardingAdapter(SimpleAttributeResolver resolver) {
			this.resolver = resolver;
		}
		
		@Override
		public Notifier getTarget() {
			return null;
		}

		@Override
		public boolean isAdapterForType(final Object type) {
			return type instanceof DiscardingAdapter;
		}

		@Override
		public void notifyChanged(final Notification notification) {
			if (!notification.isTouch() && Notification.SET == notification.getEventType()) {
				final Object feature = notification.getFeature();
				if (feature != null) {
					if (resolver.attributeName.equals(((ENamedElement) feature).getName())) {
						resolver.valueCache.discard((EObject) notification.getNotifier());
						((EObject) notification.getNotifier()).eAdapters().remove(this);
					}
				}

			}
		}

		@Override
		public void setTarget(final Notifier newTarget) {
			// nothing to do
		}
	}

	@Override
	public T apply(final K from) {
		return getValue(from);
	}

}