/*
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Aug 4, 2008
*/
package com.bigdata.btree.filter;
import java.util.Iterator;
import com.bigdata.btree.ITupleIterator;
import com.bigdata.btree.ITupleSerializer;
import com.bigdata.btree.filter.LookaheadTupleFilter.ILookaheadTupleIterator;
import cutthecrap.utils.striterators.FilterBase;
/**
* Abstract base class for an {@link ITupleFilter} that transforms the data type
* of the keys and/or values.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*
* @param E
* The generic type for the objects materialized from the source
* tuples.
* @param F
* The generic type for the objects that can be materialized from the
* output tuples.
*
* @todo better encapsulation for patterns with a 1:1 transform (one tuple in,
* one out) and patterns with a M:1 (many in, one out) and 1:M (1 in, many
* out)?
*/
abstract public class TupleTransformer<E, F> extends FilterBase implements
ITupleFilter<F> {
/** The serialization provider for the transformed tuples. */
final protected ITupleSerializer<? extends Object/*key*/,F/*val*/> tupleSer;
/**
* @param tupleSer
* The serialization provider for the transformed tuples.
*/
public TupleTransformer(
ITupleSerializer<? extends Object/* key */, F/* value */> tupleSer) {
if (tupleSer == null)
throw new IllegalArgumentException();
this.tupleSer = tupleSer;
}
/**
* @param src
* The source iterator.
*/
@SuppressWarnings("unchecked")
@Override
public ITupleIterator<F> filterOnce(Iterator src, final Object context) {
// layer in one-step lookahead.
src = new LookaheadTupleFilter().filterOnce((ITupleIterator<E>) src,
context);
// the transformer.
return newTransformer((ILookaheadTupleIterator<E>) src, context);
}
/**
* Method responsible for creating a new instance of the iterator that reads
* from the lookahead source whose tuples are of the source type and visits
* the transformed tuples.
*/
abstract protected ITupleIterator<F> newTransformer(
final ILookaheadTupleIterator<E> src, final Object context);
// /**
// * Return <code>true</code> iff another tuple of the transformed type can
// * be assembled from the source iterator.
// *
// * @param src
// * The source iterator.
// */
// abstract protected boolean hasNext(ILookaheadTupleIterator<E> src);
//
// /**
// * Implementation should consume one or more tuples from the source,
// * returning a new tuple of the target generic type.
// *
// * @param src
// * The source iterator.
// *
// * @return The transformed tuple.
// */
// abstract protected ITuple<F> next(ILookaheadTupleIterator<E> src);
// /**
// *
// * @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
// * @version $Id$
// * @param <E>
// * @param <F>
// */
// static private class Transformerator<E, F> implements ITupleIterator<F> {
//
//// private final ILookaheadTupleIterator<E> src;
//// private final TupleTransformer<E, F> filter;
// private final ITupleIterator<F> transform;
//
// /**
// *
// * @param src
// * @param filter
// */
// protected Transformerator(ITupleIterator<F> transform) {
//
// if (transform == null)
// throw new IllegalArgumentException();
//
// this.transform = transform;
//
// }
//
// public ITuple<F> next() {
//
// return transform.next();
//
// }
//
// public boolean hasNext() {
//
// return transform.hasNext();
//
// }
//
// public void remove() {
//
// throw new UnsupportedOperationException();
//
// }
//
// }
}