/*
 * 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.common.data.partition;

import edu.uci.ics.hyracks.api.comm.IFrameTupleAccessor;
import edu.uci.ics.hyracks.api.dataflow.value.IBinaryHashFunction;
import edu.uci.ics.hyracks.api.dataflow.value.IBinaryHashFunctionFactory;
import edu.uci.ics.hyracks.api.dataflow.value.ITuplePartitionComputer;
import edu.uci.ics.hyracks.api.dataflow.value.ITuplePartitionComputerFactory;

public class FieldHashPartitionComputerFactory implements ITuplePartitionComputerFactory {
    private static final long serialVersionUID = 1L;
    private final int[] hashFields;
    private final IBinaryHashFunctionFactory[] hashFunctionFactories;

    public FieldHashPartitionComputerFactory(int[] hashFields, IBinaryHashFunctionFactory[] hashFunctionFactories) {
        this.hashFields = hashFields;
        this.hashFunctionFactories = hashFunctionFactories;
    }

    @Override
    public ITuplePartitionComputer createPartitioner() {
        final IBinaryHashFunction[] hashFunctions = new IBinaryHashFunction[hashFunctionFactories.length];
        for (int i = 0; i < hashFunctionFactories.length; ++i) {
            hashFunctions[i] = hashFunctionFactories[i].createBinaryHashFunction();
        }
        return new ITuplePartitionComputer() {
            @Override
            public int partition(IFrameTupleAccessor accessor, int tIndex, int nParts) {
                if (nParts == 1) {
                    return 0;
                }
                int h = 0;
                int startOffset = accessor.getTupleStartOffset(tIndex);
                int slotLength = accessor.getFieldSlotsLength();
                for (int j = 0; j < hashFields.length; ++j) {
                    int fIdx = hashFields[j];
                    IBinaryHashFunction hashFn = hashFunctions[j];
                    int fStart = accessor.getFieldStartOffset(tIndex, fIdx);
                    int fEnd = accessor.getFieldEndOffset(tIndex, fIdx);
                    int fh = hashFn
                            .hash(accessor.getBuffer().array(), startOffset + slotLength + fStart, fEnd - fStart);
                    h = h * 31 + fh;
                }
                if (h < 0) {
                    h = -(h + 1);
                }
                return h % nParts;
            }
        };
    }
}