NullIndexer.java

/*******************************************************************************
 * Copyright (c) 2004-2012 Gabor Bergmann and Daniel Varro
 * 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:
 *    Gabor Bergmann - initial API and implementation
 *******************************************************************************/

package org.eclipse.incquery.runtime.rete.index;

import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;

import org.eclipse.incquery.runtime.rete.network.Direction;
import org.eclipse.incquery.runtime.rete.network.Node;
import org.eclipse.incquery.runtime.rete.network.ReteContainer;
import org.eclipse.incquery.runtime.rete.network.Supplier;
import org.eclipse.incquery.runtime.rete.tuple.FlatTuple;
import org.eclipse.incquery.runtime.rete.tuple.Tuple;
import org.eclipse.incquery.runtime.rete.tuple.TupleMask;

/**
 * Defines an abstract trivial indexer that projects the contents of some stateful node to the empty tuple, and can
 * therefore save space. Can only exist in connection with a stateful store, and must be operated by another node (the
 * active node). Do not attach parents directly!
 * 
 * @author Bergmann Gábor
 */
public abstract class NullIndexer extends SpecializedProjectionIndexer {

    protected abstract Collection<Tuple> getTuples();

    static Object[] empty = {};
    static Tuple nullSignature = new FlatTuple(empty);
    static Collection<Tuple> nullSingleton = Collections.singleton(nullSignature);
    static Collection<Tuple> emptySet = Collections.emptySet();

    public NullIndexer(ReteContainer reteContainer, int tupleWidth, Supplier parent, Node activeNode) {
        super(reteContainer, TupleMask.linear(0, tupleWidth), parent, activeNode);
    }

    public Collection<Tuple> get(Tuple signature) {
        if (nullSignature.equals(signature))
            return isEmpty() ? null : getTuples();
        else
            return null;
    }

    public Collection<Tuple> getSignatures() {
        return isEmpty() ? emptySet : nullSingleton;
    }

    /**
     * @return
     */
    protected boolean isEmpty() {
        return getTuples().isEmpty();
    }

    protected boolean isSingleElement() {
        return getTuples().size() == 1;
    }

    public Iterator<Tuple> iterator() {
        return getTuples().iterator();
    }

    public void propagate(Direction direction, Tuple updateElement) {
        boolean radical = (direction == Direction.REVOKE && isEmpty())
                || (direction == Direction.INSERT && isSingleElement());
        propagate(direction, updateElement, nullSignature, radical);
    }

}