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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 at
 *
 *     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 org.apache.cassandra.db.aggregation;

import java.nio.ByteBuffer;
import java.util.List;

import org.apache.cassandra.cql3.selection.Selector;
import org.apache.cassandra.db.Clustering;
import org.apache.cassandra.db.ClusteringComparator;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.schema.ColumnMetadata;
import org.apache.cassandra.transport.ProtocolVersion;

/**
 * A GroupMaker can be used to determine if some sorted rows belongs to the same group or not.
 */
public abstract class GroupMaker
{
    /**
     * GroupMaker that groups all the rows together.
     */
    public static final GroupMaker GROUP_EVERYTHING = new GroupMaker()
    {
        public boolean isNewGroup(DecoratedKey partitionKey, Clustering clustering)
        {
            return false;
        }

        public boolean returnAtLeastOneRow()
        {
            return true;
        }
    };

    public static GroupMaker newPkPrefixGroupMaker(ClusteringComparator comparator,
                                                   int clusteringPrefixSize,
                                                   GroupingState state)
    {
        return new PkPrefixGroupMaker(comparator, clusteringPrefixSize, state);
    }

    public static GroupMaker newPkPrefixGroupMaker(ClusteringComparator comparator, int clusteringPrefixSize)
    {
        return new PkPrefixGroupMaker(comparator, clusteringPrefixSize);
    }

    public static GroupMaker newSelectorGroupMaker(ClusteringComparator comparator,
                                                   int clusteringPrefixSize,
                                                   Selector selector,
                                                   List columns,
                                                   GroupingState state)
    {
        return new SelectorGroupMaker(comparator, clusteringPrefixSize, selector, columns, state);
    }

    public static GroupMaker newSelectorGroupMaker(ClusteringComparator comparator,
                                                   int clusteringPrefixSize,
                                                   Selector selector,
                                                   List columns)
    {
        return new SelectorGroupMaker(comparator, clusteringPrefixSize, selector, columns);
    }

    /**
     * Checks if a given row belongs to the same group that the previous row or not.
     *
     * @param partitionKey the partition key.
     * @param clustering the row clustering key
     * @return true if the row belongs to the same group that the previous one, false
     * otherwise.
     */
    public abstract boolean isNewGroup(DecoratedKey partitionKey, Clustering clustering);

    /**
     * Specify if at least one row must be returned. If the selection is performing some aggregations on all the rows,
     * one row should be returned even if no records were processed.
     *
     * @return true if at least one row must be returned, false otherwise.
     */
    public boolean returnAtLeastOneRow()
    {
        return false;
    }

    private static class PkPrefixGroupMaker extends GroupMaker
    {
        /**
         * The size of the clustering prefix used to make the groups
         */
        protected final int clusteringPrefixSize;

        /**
         * The comparator used to compare the clustering prefixes.
         */
        protected final ClusteringComparator comparator;

        /**
         * The last partition key seen
         */
        protected ByteBuffer lastPartitionKey;

        /**
         * The last clustering seen
         */
        protected Clustering lastClustering;

        public PkPrefixGroupMaker(ClusteringComparator comparator, int clusteringPrefixSize, GroupingState state)
        {
            this(comparator, clusteringPrefixSize);
            this.lastPartitionKey = state.partitionKey();
            this.lastClustering = state.clustering;
        }

        public PkPrefixGroupMaker(ClusteringComparator comparator, int clusteringPrefixSize)
        {
            this.comparator = comparator;
            this.clusteringPrefixSize = clusteringPrefixSize;
        }

        @Override
        public boolean isNewGroup(DecoratedKey partitionKey, Clustering clustering)
        {
            ByteBuffer key = partitionKey.getKey();
            // We are entering a new group if:
            // - the partition key is a new one
            // - the last clustering was not null and does not have the same prefix as the new clustering one
            boolean isNew = !key.equals(lastPartitionKey)
                            || lastClustering == null
                            || comparator.compare(lastClustering, clustering, clusteringPrefixSize) != 0;

            lastPartitionKey = key;
            lastClustering =  Clustering.STATIC_CLUSTERING == clustering ? null : clustering;
            return isNew;
        }
    }

    private static class SelectorGroupMaker extends PkPrefixGroupMaker
    {
        /**
         * The selector used to build the groups.
         */
        private final Selector selector;

        /**
         * The output of the selector call on the last clustering
         */
        private ByteBuffer lastOutput;

        private final Selector.InputRow input;

        public SelectorGroupMaker(ClusteringComparator comparator,
                                  int clusteringPrefixSize,
                                  Selector selector,
                                  List columns,
                                  GroupingState state)
        {
            super(comparator, clusteringPrefixSize, state);
            this.selector = selector;
            this.input = new Selector.InputRow(ProtocolVersion.CURRENT, columns, false);
            this.lastOutput = lastClustering == null ? null :
                                                       executeSelector(lastClustering.bufferAt(clusteringPrefixSize - 1));
        }

        public SelectorGroupMaker(ClusteringComparator comparator,
                                  int clusteringPrefixSize,
                                  Selector selector,
                                  List columns)
        {
            super(comparator, clusteringPrefixSize);
            this.selector = selector;
            this.input = new Selector.InputRow(ProtocolVersion.CURRENT, columns, false);
        }

        @Override
        public boolean isNewGroup(DecoratedKey partitionKey, Clustering clustering)
        {
            ByteBuffer output =
                    Clustering.STATIC_CLUSTERING == clustering ? null
                                                               : executeSelector(clustering.bufferAt(clusteringPrefixSize - 1));

            ByteBuffer key = partitionKey.getKey();

            // We are entering a new group if:
            // - the partition key is a new one
            // - the last clustering was not null and does not have the same prefix as the new clustering one
            boolean isNew = !key.equals(lastPartitionKey)
                            || lastClustering == null
                            || comparator.compare(lastClustering, clustering, clusteringPrefixSize - 1) != 0
                            || compareOutput(output) != 0;

            lastPartitionKey = key;
            lastClustering = Clustering.STATIC_CLUSTERING == clustering ? null : clustering;
            lastOutput = output;
            return isNew;
        }

        private int compareOutput(ByteBuffer output)
        {
            if (output == null)
                return lastOutput == null ? 0 : -1;
            if (lastOutput == null)
                return 1;

            return selector.getType().compare(output, lastOutput);
        }

        private ByteBuffer executeSelector(ByteBuffer argument)
        {
            input.add(argument);

            // For computing groups we do not need to use the client protocol version.
            selector.addInput(input);
            ByteBuffer output = selector.getOutput(ProtocolVersion.CURRENT);
            selector.reset();
            input.reset(false);

            return output;
        }
    }
}