/*
 * 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.kylin.source.hive.cardinality;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.kylin.engine.mr.KylinReducer;
import org.apache.kylin.measure.BufferedMeasureCodec;
import org.apache.kylin.measure.hllc.HLLCounter;

/**
 * @author Jack
 * 
 */
public class ColumnCardinalityReducer extends KylinReducer<IntWritable, BytesWritable, IntWritable, LongWritable> {

    public static final int ONE = 1;
    private Map<Integer, HLLCounter> hllcMap = new HashMap<Integer, HLLCounter>();

    @Override
    protected void setup(Context context) throws IOException {
        super.bindCurrentConfiguration(context.getConfiguration());
    }

    @Override
    public void doReduce(IntWritable key, Iterable<BytesWritable> values, Context context) throws IOException, InterruptedException {
        int skey = key.get();
        for (BytesWritable v : values) {
            ByteBuffer buffer = ByteBuffer.wrap(v.getBytes());
            HLLCounter hll = new HLLCounter();
            hll.readRegisters(buffer);
            getHllc(skey).merge(hll);
            hll.clear();
        }
    }

    private HLLCounter getHllc(Integer key) {
        if (!hllcMap.containsKey(key)) {
            hllcMap.put(key, new HLLCounter());
        }
        return hllcMap.get(key);
    }

    @Override
    protected void doCleanup(Context context) throws IOException, InterruptedException {
        List<Integer> keys = new ArrayList<Integer>();
        Iterator<Integer> it = hllcMap.keySet().iterator();
        while (it.hasNext()) {
            keys.add(it.next());
        }
        Collections.sort(keys);
        it = keys.iterator();
        while (it.hasNext()) {
            int key = it.next();
            HLLCounter hllc = hllcMap.get(key);
            ByteBuffer buf = ByteBuffer.allocate(BufferedMeasureCodec.DEFAULT_BUFFER_SIZE);
            buf.clear();
            hllc.writeRegisters(buf);
            buf.flip();
            context.write(new IntWritable(key), new LongWritable(hllc.getCountEstimate()));
        }
    }
}