/*
 * Copyright (c) 2008-2017, Hazelcast, Inc. All Rights Reserved.
 *
 * 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 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 com.hazelcast.mapreduce.aggregation.impl;

import com.hazelcast.mapreduce.Collator;
import com.hazelcast.mapreduce.Combiner;
import com.hazelcast.mapreduce.CombinerFactory;
import com.hazelcast.mapreduce.Mapper;
import com.hazelcast.mapreduce.Reducer;
import com.hazelcast.mapreduce.ReducerFactory;
import com.hazelcast.mapreduce.aggregation.Supplier;
import com.hazelcast.nio.serialization.BinaryInterface;

import java.math.BigDecimal;
import java.util.Map;

/**
 * The predefined average aggregation for values of type {@link java.math.BigDecimal}.
 *
 * @param <Key>   the input key type
 * @param <Value> the input value type
 */
public class BigDecimalAvgAggregation<Key, Value>
        implements AggType<Key, Value, Key, BigDecimal, AvgTuple<Long, BigDecimal>, AvgTuple<Long, BigDecimal>, BigDecimal> {

    @Override
    public Collator<Map.Entry<Key, AvgTuple<Long, BigDecimal>>, BigDecimal> getCollator() {
        return new Collator<Map.Entry<Key, AvgTuple<Long, BigDecimal>>, BigDecimal>() {
            @Override
            public BigDecimal collate(Iterable<Map.Entry<Key, AvgTuple<Long, BigDecimal>>> values) {
                long count = 0;
                BigDecimal amount = BigDecimal.ZERO;
                for (Map.Entry<Key, AvgTuple<Long, BigDecimal>> entry : values) {
                    AvgTuple<Long, BigDecimal> tuple = entry.getValue();
                    count += tuple.getFirst();
                    amount = amount.add(tuple.getSecond());
                }
                return amount.divide(BigDecimal.valueOf(count));
            }
        };
    }

    @Override
    public Mapper<Key, Value, Key, BigDecimal> getMapper(Supplier<Key, Value, BigDecimal> supplier) {
        return new SupplierConsumingMapper<Key, Value, BigDecimal>(supplier);
    }

    @Override
    public CombinerFactory<Key, BigDecimal, AvgTuple<Long, BigDecimal>> getCombinerFactory() {
        return new BigDecimalAvgCombinerFactory<Key>();
    }

    @Override
    public ReducerFactory<Key, AvgTuple<Long, BigDecimal>, AvgTuple<Long, BigDecimal>> getReducerFactory() {
        return new BigDecimalAvgReducerFactory<Key>();
    }

    /**
     * Average CombinerFactory for type {@link java.math.BigDecimal}
     *
     * @param <Key> the key type
     */
    @BinaryInterface
    static final class BigDecimalAvgCombinerFactory<Key>
            extends AbstractAggregationCombinerFactory<Key, BigDecimal, AvgTuple<Long, BigDecimal>> {

        @Override
        public Combiner<BigDecimal, AvgTuple<Long, BigDecimal>> newCombiner(Key key) {
            return new BigDecimalAvgCombiner();
        }

        @Override
        public int getId() {
            return AggregationsDataSerializerHook.BIG_DECIMAL_AVG_COMBINER_FACTORY;
        }
    }

    /**
     * Average ReducerFactory for type {@link java.math.BigDecimal}
     *
     * @param <Key> the key type
     */
    @BinaryInterface
    static final class BigDecimalAvgReducerFactory<Key>
            extends AbstractAggregationReducerFactory<Key, AvgTuple<Long, BigDecimal>, AvgTuple<Long, BigDecimal>> {

        @Override
        public Reducer<AvgTuple<Long, BigDecimal>, AvgTuple<Long, BigDecimal>> newReducer(Key key) {
            return new BigDecimalAvgReducer();
        }

        @Override
        public int getId() {
            return AggregationsDataSerializerHook.BIG_DECIMAL_AVG_REDUCER_FACTORY;
        }
    }

    /**
     * Average Combiner for type {@link java.math.BigDecimal}
     */
    private static final class BigDecimalAvgCombiner
            extends Combiner<BigDecimal, AvgTuple<Long, BigDecimal>> {

        private long count;
        private BigDecimal amount = BigDecimal.ZERO;

        @Override
        public void combine(BigDecimal value) {
            count++;
            amount = amount.add(value);
        }

        @Override
        public AvgTuple<Long, BigDecimal> finalizeChunk() {
            return new AvgTuple<Long, BigDecimal>(count, amount);
        }

        @Override
        public void reset() {
            count = 0;
            amount = BigDecimal.ZERO;
        }
    }

    /**
     * Average Reducer for type {@link java.math.BigDecimal}
     */
    private static final class BigDecimalAvgReducer
            extends Reducer<AvgTuple<Long, BigDecimal>, AvgTuple<Long, BigDecimal>> {

        private long count;
        private BigDecimal amount = BigDecimal.ZERO;

        @Override
        public void reduce(AvgTuple<Long, BigDecimal> value) {
            count += value.getFirst();
            amount = amount.add(value.getSecond());
        }

        @Override
        public AvgTuple<Long, BigDecimal> finalizeReduce() {
            return new AvgTuple<Long, BigDecimal>(count, amount);
        }
    }
}