/*
 * 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.Arrays;

import org.apache.cassandra.db.Clustering;
import org.apache.cassandra.db.ClusteringComparator;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.utils.ByteBufferUtil;

A GroupMaker can be used to determine if some sorted rows belongs to the same group or not.
/**
 * A <code>GroupMaker</code> 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.
/**
     * <code>GroupMaker</code> 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 newInstance(ClusteringComparator comparator, int clusteringPrefixSize, GroupingState state)
    {
        return new PkPrefixGroupMaker(comparator, clusteringPrefixSize, state);
    }

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

    
Checks if a given row belongs to the same group that the previous row or not.
Params:
partitionKey – the partition key.
clustering – the row clustering key
Returns:
true if the row belongs to the same group that the previous one, false
otherwise./**
     * 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 <code>true</code> if the row belongs to the same group that the previous one, <code>false</code>
     * 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.
Returns:
true if at least one row must be returned, false otherwise./**
     * 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 <code>true</code> if at least one row must be returned, <code>false</code> otherwise.
     */
    public boolean returnAtLeastOneRow()
    {
        return false;
    }

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

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

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

        
The last clustering seen
/**
         * The last clustering seen
         */
        private 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)
        {
            boolean isNew = false;

            // 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
            if (!partitionKey.getKey().equals(lastPartitionKey))
            {
                lastPartitionKey = partitionKey.getKey();
                isNew = true;
                if (Clustering.STATIC_CLUSTERING == clustering)
                {
                    lastClustering = null;
                    return true;
                }
            }
            else if (lastClustering != null && comparator.compare(lastClustering, clustering, clusteringPrefixSize) != 0)
            {
                isNew = true;
            }

            lastClustering = clustering;
            return isNew;
        }
    }
}