#include "gtl_math.h"
#include <vector>
#include <QtMath>
#include <numeric>

mathFunctions::mathFunctions()
{
}

qreal mathFunctions::squared_sum(const std::vector<qreal>::iterator &begin, const std::vector<qreal>::iterator &end)
{
    qreal sum = 0;
    for(auto it = begin; it != end; ++it) {
        sum += qPow(*it, 2);
    }
    return sum;
}

qreal mathFunctions::rms(const std::vector<qreal>::iterator &begin, const std::vector<qreal>::iterator &end)
{
    return qSqrt(mathFunctions::squared_sum(begin, end)/std::distance(begin,end));
}

qreal mathFunctions::max(const std::vector<qreal>::iterator &begin, const std::vector<qreal>::iterator &end)
{
    return *std::max_element(begin, end);
}

qreal mathFunctions::min(const std::vector<qreal>::iterator &begin, const std::vector<qreal>::iterator &end)
{
    return *std::min_element(begin, end);
}

qreal mathFunctions::mean(const std::vector<qreal>::iterator &begin, const std::vector<qreal>::iterator &end)
{
    return std::accumulate(begin, end, 0.)/std::distance(begin, end);
}

qreal mathFunctions::kurt(const std::vector<qreal>::iterator &begin, const std::vector<qreal>::iterator &end)
{
    qreal value = 0;
    int n = std::distance(begin, end);
    if(n > 3)
    {
        qreal mean = mathFunctions::mean(begin, end);
        qreal variance = 0.;
        for(auto it = begin; it != end; ++it)
            variance += pow((*it - mean), 2);
        variance /= n;

        qreal sigma = 0;
        for(auto it = begin; it != end; ++it)
            sigma += pow((*it - mean), 4);

        sigma /= n;

        qreal k1 = (qreal)(n*n - 1) / (qreal)((n-2)*(n-3));
        qreal k2 = (qreal)((6. / (n + 1.)) - 3.);

        value = k1*(sigma/pow(variance,2) + k2);

    }
    return value;
}

qreal mathFunctions::var(const std::vector<qreal>::iterator &begin, const std::vector<qreal>::iterator &end)
{
    int n = std::distance(begin, end);

    qreal mean  = std::accumulate(begin, end, 0.)/n;

    qreal v = 0.;
    for(auto it = begin; it != end; ++it)
        v += qPow((*it - mean), 2);
    v /= n-1;

    return v;
}