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/*
 * Copyright (c) 2000, 2020, Oracle and/or its affiliates.
 *
 * Licensed under the Universal Permissive License v 1.0 as shown at
 * http://oss.oracle.com/licenses/upl.
 */

package com.tangosol.util.aggregator;


import com.tangosol.internal.util.aggregator.BigDecimalSerializationWrapper;
import com.tangosol.util.InvocableMap;
import com.tangosol.util.ValueExtractor;

import java.math.BigDecimal;


/**
* Calculates an average for values of any numeric type extracted from a set
* of entries in a Map in a form of a {@link java.math.BigDecimal} value.  All
* the extracted objects will be treated as {@link java.math.BigDecimal},
* {@link java.math.BigInteger} or Java double values.
* If the set of entries is empty, a null result is returned.
*
* @param   the type of the value to extract from
*
* @author gg  2006.07.18
* @since Coherence 3.2
*/
public class BigDecimalAverage
        extends AbstractBigDecimalAggregator
    {
    // ----- constructors ---------------------------------------------------

    /**
    * Default constructor (necessary for the ExternalizableLite interface).
    */
    public BigDecimalAverage()
        {
        super();
        }

    /**
    * Construct a BigDecimalAverage aggregator.
    *
    * @param extractor  the extractor that provides a value in the form of
    *                   any Java object that is a {@link Number}
    */
    public BigDecimalAverage(ValueExtractor extractor)
        {
        super(extractor);
        }

    /**
    * Construct an BigDecimalAverage object.
    *
    * @param sMethod  the name of the method that returns a value in the form
    *                 of any Java object that is a {@link Number}
    */
    public BigDecimalAverage(String sMethod)
        {
        super(sMethod);
        }

    // ----- StreamingAggregator methods ------------------------------------

    @Override
    public InvocableMap.StreamingAggregator supply()
        {
        return new BigDecimalAverage<>(getValueExtractor());
        }

    @Override
    public int characteristics()
        {
        return PARALLEL | PRESENT_ONLY;
        }

    // ----- AbstractAggregator methods -------------------------------------

    /**
    * {@inheritDoc}
    */
    protected void process(Object o, boolean fFinal)
        {
        if (o != null)
            {
            BigDecimal decResult = m_decResult;

            if (fFinal)
                {
                BigDecimalSerializationWrapper wrapper = (BigDecimalSerializationWrapper) o;
                int c = wrapper.getCount();
                if (c > 0)
                    {
                    m_count += c;
                    BigDecimal partialResult = wrapper.getBigDecimal();
                    m_decResult = decResult == null ? partialResult : decResult.add(partialResult);
                    }
                }
            else
                {
                BigDecimal dec = ensureBigDecimal((Number) o);

                // collect partial results
                m_count++;
                m_decResult = decResult == null ? dec : decResult.add(dec);
                }
            }
        }

    /**
    * {@inheritDoc}
    */
    protected Object finalizeResult(boolean fFinal)
        {
        int        c         = m_count;
        BigDecimal decResult = m_decResult;

        if (fFinal)
            {
            // return the final aggregated result
            return c == 0 ? null :
                decResult.divide(BigDecimal.valueOf(c),
                    decResult.scale() + 8, // 'cause Cam said so
                    BigDecimal.ROUND_HALF_UP);
            }
        else
            {
            // return partial aggregation data wrapped in SerializationWrapper to ensure
            // there's enough context for all serialization formats to function as expected.
            return c > 0 ? new BigDecimalSerializationWrapper(m_count, m_decResult) : null;
            }
        }
    }