/*
 * Copyright 2009-2010 by The Regents of the University of California
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * you may obtain a copy of the License from
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package edu.uci.ics.hyracks.dataflow.hadoop.data;

import java.io.DataInputStream;

import org.apache.hadoop.io.Writable;

import edu.uci.ics.hyracks.api.comm.IFrameTupleAccessor;
import edu.uci.ics.hyracks.api.dataflow.value.ISerializerDeserializer;
import edu.uci.ics.hyracks.api.dataflow.value.ITuplePartitionComputer;
import edu.uci.ics.hyracks.api.dataflow.value.ITuplePartitionComputerFactory;
import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
import edu.uci.ics.hyracks.dataflow.common.comm.util.ByteBufferInputStream;

public class HadoopHashTuplePartitionComputerFactory<K extends Writable> implements ITuplePartitionComputerFactory {
    private static final long serialVersionUID = 1L;
    private final ISerializerDeserializer<K> keyIO;

    public HadoopHashTuplePartitionComputerFactory(ISerializerDeserializer<K> keyIO) {
        this.keyIO = keyIO;
    }

    @Override
    public ITuplePartitionComputer createPartitioner() {
        return new ITuplePartitionComputer() {
            private final ByteBufferInputStream bbis = new ByteBufferInputStream();
            private final DataInputStream dis = new DataInputStream(bbis);

            @Override
            public int partition(IFrameTupleAccessor accessor, int tIndex, int nParts) throws HyracksDataException {
                int keyStart = accessor.getTupleStartOffset(tIndex) + accessor.getFieldSlotsLength()
                        + accessor.getFieldStartOffset(tIndex, 0);
                bbis.setByteBuffer(accessor.getBuffer(), keyStart);
                K key = keyIO.deserialize(dis);
                int h = key.hashCode();
                if (h < 0) {
                    h = -h;
                }
                return h % nParts;
            }
        };
    }
}