/*
 * Copyright 2009-2013 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.pregelix.dataflow.std.group;

import edu.uci.ics.hyracks.api.comm.IFrameTupleAccessor;
import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
import edu.uci.ics.hyracks.dataflow.common.comm.io.FrameTupleAppender;
import edu.uci.ics.hyracks.dataflow.std.group.AggregateState;

public interface IAggregatorDescriptor {

    /**
     * Create an aggregate state
     * 
     * @return
     */
    public AggregateState createAggregateStates();

    /**
     * Initialize the state based on the input tuple.
     * 
     * @param accessor
     * @param tIndex
     * @param fieldOutput
     *            The data output for the frame containing the state. This may
     *            be null, if the state is maintained as a java object
     * @param state
     *            The state to be initialized.
     * @throws HyracksDataException
     */
    public void init(IFrameTupleAccessor accessor, int tIndex, AggregateState state) throws HyracksDataException;

    /**
     * Reset the aggregator. The corresponding aggregate state should be reset
     * too. Note that here the frame is not an input argument, since it can be
     * reset outside of the aggregator (simply reset the starting index of the
     * buffer).
     * 
     * @param state
     */
    public void reset();

    /**
     * Aggregate the value. Aggregate state should be updated correspondingly.
     * 
     * @param accessor
     * @param tIndex
     * @param data
     *            The buffer containing the state, if frame-based-state is used.
     *            This means that it can be null if java-object-based-state is
     *            used.
     * @param offset
     * @param state
     *            The aggregate state.
     * @throws HyracksDataException
     */
    public void aggregate(IFrameTupleAccessor accessor, int tIndex, AggregateState state) throws HyracksDataException;

    /**
     * Output the partial aggregation result.
     * 
     * @param fieldOutput
     *            The data output for the output frame
     * @param data
     *            The buffer containing the aggregation state
     * @param offset
     * @param state
     *            The aggregation state.
     * @return TODO
     * @throws HyracksDataException
     */
    public boolean outputPartialResult(IFrameTupleAccessor accessor, int tIndex, AggregateState state,
            FrameTupleAppender appender) throws HyracksDataException;

    /**
     * Output the final aggregation result.
     * 
     * @param fieldOutput
     *            The data output for the output frame
     * @param data
     *            The buffer containing the aggregation state
     * @param offset
     * @param state
     *            The aggregation state.
     * @return true if the group is already written; false--left for the group writer to write the grouped tuple
     * @throws HyracksDataException
     */
    public boolean outputFinalResult(IFrameTupleAccessor accessor, int tIndex, AggregateState state,
            FrameTupleAppender appender) throws HyracksDataException;

    public void close();

}