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/**

Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016.  All rights reserved.

Contact:
     SYSTAP, LLC DBA Blazegraph
     2501 Calvert ST NW #106
     Washington, DC 20008
     [email protected]

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 Oct 29, 2011
 */

package com.bigdata.bop.solutions;

import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

import com.bigdata.bop.BOp;
import com.bigdata.bop.BOpContext;
import com.bigdata.bop.IBindingSet;
import com.bigdata.bop.IVariable;
import com.bigdata.bop.NV;
import com.bigdata.bop.PipelineOp;
import com.bigdata.bop.engine.BOpStats;
import com.bigdata.bop.join.JoinAnnotations;
import com.bigdata.relation.accesspath.IBlockingBuffer;

import cutthecrap.utils.striterators.ICloseableIterator;

/**
 * Operator projects only the identified variables.
 * 
 * @author Bryan Thompson
 * @version $Id$
 */
public class ProjectionOp extends PipelineOp {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public interface Annotations extends PipelineOp.Annotations {

        /**
         * An {@link IVariable}[] identifying the variables to be retained in
         * the {@link IBindingSet}s written out by the operator.
         */
        String SELECT = JoinAnnotations.SELECT;
    }
    
    /**
     * @param op
     */
    public ProjectionOp(final ProjectionOp op) {
        super(op);
    }

    /**
     * @param args
     * @param annotations
     */
    public ProjectionOp(final BOp[] args, final Map annotations) {
        super(args, annotations);
    }

    public ProjectionOp(final BOp[] args, final NV... annotations) {

        this(args, NV.asMap(annotations));
        
    }

    /**
     * @see Annotations#SELECT
     */
    public IVariable[] getVariables() {

        return (IVariable[]) getRequiredProperty(Annotations.SELECT);
        
    }

    @Override
    public FutureTask eval(final BOpContext context) {

        return new FutureTask(new ChunkTask(this, context));
        
    }

    /**
     * Task executing on the node.
     */
    static private class ChunkTask implements Callable {

        private final BOpContext context;

        /**
         * The projected variables.
         */
        private final IVariable[] vars;

        ChunkTask(final ProjectionOp op, final BOpContext context) {

            this.context = context;

            this.vars = op.getVariables();

            if (vars == null)
                throw new IllegalArgumentException();

            // @see #946 (Empty PROJECTION causes IllegalArgumentException)
//            if (vars.length == 0)
//                throw new IllegalArgumentException();

        }

        @Override
        public Void call() throws Exception {

            final BOpStats stats = context.getStats();

            final ICloseableIterator itr = context
                    .getSource();

            final IBlockingBuffer sink = context.getSink();

            try {

                while (itr.hasNext()) {

                    final IBindingSet[] a = itr.next();

                    stats.chunksIn.increment();
                    stats.unitsIn.add(a.length);

                    for (int i = 0; i < a.length; i++) {

                        a[i] = a[i].copy(vars);

                    }
                    
                    sink.add(a);

                }

                sink.flush();

                // done.
                return null;

            } finally {

                sink.close();

            }

        }

    }

}