/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2016 - ROLI Ltd.

   Permission is granted to use this software under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license/

   Permission to use, copy, modify, and/or distribute this software for any
   purpose with or without fee is hereby granted, provided that the above
   copyright notice and this permission notice appear in all copies.

   THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH REGARD
   TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
   FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT,
   OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
   USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
   TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
   OF THIS SOFTWARE.

   -----------------------------------------------------------------------------

   To release a closed-source product which uses other parts of JUCE not
   licensed under the ISC terms, commercial licenses are available: visit
   www.juce.com for more information.

  ==============================================================================
*/

#ifndef JUCE_STATISTICSACCUMULATOR_H_INCLUDED
#define JUCE_STATISTICSACCUMULATOR_H_INCLUDED


//==============================================================================
/**
    A class that measures various statistics about a series of floating point
    values that it is given.
*/
template <typename FloatType>
class StatisticsAccumulator
{
public:
    //==============================================================================
    /** Constructs a new StatisticsAccumulator. */
    StatisticsAccumulator() noexcept
        : count (0),
          minimum ( std::numeric_limits<FloatType>::infinity()),
          maximum (-std::numeric_limits<FloatType>::infinity())
    {}

    //==============================================================================
    /** Add a new value to the accumulator.
        This will update all running statistics accordingly.
    */
    void addValue (FloatType v) noexcept
    {
        jassert (juce_isfinite (v));

        sum += v;
        sumSquares += v * v;
        ++count;

        if (v > maximum) maximum = v;
        if (v < minimum) minimum = v;
    }

    /** Reset the accumulator.
        This will reset all currently saved statistcs.
    */
    void reset() noexcept               { *this = StatisticsAccumulator<FloatType>(); }

    //==============================================================================
    /** Returns the average (arithmetic mean) of all previously added values.
        If no values have been added yet, this will return zero.
    */
    FloatType getAverage() const noexcept
    {
        return count > 0 ? sum / (FloatType) count
                         : FloatType();
    }

    /** Returns the variance of all previously added values.
        If no values have been added yet, this will return zero.
    */
    FloatType getVariance() const noexcept
    {
        return count > 0 ? (sumSquares - sum * sum / (FloatType) count) / (FloatType) count
                         : FloatType();
    }

    /** Returns the standard deviation of all previously added values.
        If no values have been added yet, this will return zero.
    */
    FloatType getStandardDeviation() const noexcept
    {
        return std::sqrt (getVariance());
    }

    /** Returns the smallest of all previously added values.
        If no values have been added yet, this will return positive infinity.
    */
    FloatType getMinValue() const noexcept
    {
        return minimum;
    }

    /** Returns the largest of all previously added values.
        If no values have been added yet, this will return negative infinity.
    */
    FloatType getMaxValue() const noexcept
    {
        return maximum;
    }

    /** Returns how many values have been added to this accumulator. */
    size_t getCount() const noexcept
    {
        return count;
    }

private:
    //==============================================================================
    struct KahanSum
    {
        KahanSum() noexcept : sum(), error() {}
        operator FloatType() const noexcept             { return sum; }

        void JUCE_NO_ASSOCIATIVE_MATH_OPTIMISATIONS operator+= (FloatType value) noexcept
        {
            FloatType correctedValue = value - error;
            FloatType newSum = sum + correctedValue;
            error = (newSum - sum) - correctedValue;
            sum = newSum;
        }

        FloatType sum, error;
    };

    //==============================================================================
    size_t count;
    KahanSum sum, sumSquares;
    FloatType minimum, maximum;
};


#endif   // JUCE_STATISTICSACCUMULATOR_H_INCLUDED
