/***********************************************************************
 * 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.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;

/**
 * Introduces the notation of many-to-one relation. This is where the M and O of
 * the type signature comes from.
 * 
 * Many unique "source" objects refer to one and only "target" object.
 * 
 * The class maintains a connection between the target and all the sources that
 * are referring to it.
 * 
 * @author Kiril Mitov k.mitov@sap.com
 * 
 * @param <M>
 *            the type of the "source" objects.
 * @param <O>
 *            the type of the "target" objects.
 */
public class ManyToOneRelation<M, O> {

	private Map<M, O> manyToOne = new HashMap<M, O>();

	/**
	 * Connects the given source with the given target. If this source was
	 * previously connected with another target the old connection is lost.
	 * 
	 * @param source
	 * @param target
	 * @return
	 */
	public boolean connect(M source, O target) {
		manyToOne.put(source, target);
		return false;
	}

	/**
	 * @param source
	 * @return <code>true</code> if the relation contains the given source
	 */
	public boolean containsSource(M source) {
		return manyToOne.containsKey(source);
	}

	/**
	 * @param target
	 * @return <code>true</code> if the relation contains the given target
	 */
	public boolean containsTarget(O target) {
		return manyToOne.containsValue(target);
	}

	/**
	 * @param source
	 * @return the target with which this source is connected
	 */
	public O getTarget(M source) {
		return manyToOne.get(source);
	}

	/**
	 * @param target
	 * @return all the targets that are connected with this source or empty
	 *         collection if there are no sources connected with this target.
	 */
	public Collection<M> getSources(O target) {
		Collection<M> files = new LinkedList<M>();
		for (Map.Entry<M, O> entry : manyToOne.entrySet()) {
			if (entry.getValue().equals(target))
				files.add(entry.getKey());
		}
		return files;
	}

	/**
	 * Removes the connection between this source and the corresponding target.
	 * Other sources will still point to the same target.
	 * 
	 * The target is removed if this was the only source pointing to it and
	 * {@link #containsTarget(Object)} will return false.
	 * 
	 * @param source
	 */
	public void disconnectSource(M source) {
		manyToOne.remove(source);
	}

	/**
	 * Removes the given target from the relation. All the sources that are
	 * pointing to this target are also removed.
	 * 
	 * If you take the "result" of {@link #getSources(target)} and after that
	 * call this method then {@link #containsSource(Object)} will return
	 * <code>false</code> for every object in "result".
	 * 
	 * @param target
	 */
	public void disconnect(O target) {
		for (Iterator<O> iter = manyToOne.values().iterator(); iter.hasNext();) {
			if (iter.next().equals(target))
				iter.remove();
		}
	}

	/**
	 * @return a collection of the targets.
	 */
	public Collection<O> getTargets() {
		return manyToOne.values();
	}

}