// *****************************************************************************
// * This file is part of the FreeFileSync project. It is distributed under    *
// * GNU General Public License: https://www.gnu.org/licenses/gpl-3.0          *
// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
// *****************************************************************************

#include "speed_test.h"
#include <zen/basic_math.h>
#include <zen/i18n.h>
#include <zen/format_unit.h>

using namespace zen;
using namespace fff;


void SpeedTest::addSample(std::chrono::nanoseconds timeElapsed, int itemsCurrent, int64_t bytesCurrent)
{
    //time expected to be monotonously ascending
    assert(samples_.empty() || samples_.back().timeElapsed <= timeElapsed);

    samples_.push_back(Sample{timeElapsed, itemsCurrent, bytesCurrent});

    //remove old records outside of "window"
    std::optional<Sample> lastPop;
    while (!samples_.empty() && samples_.front().timeElapsed <= timeElapsed - windowSize_)
    {
        lastPop = samples_.front();
        samples_.pop_front();
    }
    if (lastPop) //keep one point before new start to handle gaps
        samples_.push_front(*lastPop);
}


std::optional<double> SpeedTest::getRemainingSec(int /*itemsRemaining*/, int64_t bytesRemaining) const
{
    if (!samples_.empty())
    {
        const double timeDelta = std::chrono::duration<double>(samples_.back().timeElapsed - samples_.front().timeElapsed).count();
        const int64_t bytesDelta = samples_.back().bytes - samples_.front().bytes;

        //"items" counts logical operations *NOT* disk accesses, so we better play safe and use "bytes" only!

        if (bytesDelta != 0) //sign(dataRemaining) != sign(bytesDelta) usually an error, so show it!
            return bytesRemaining * timeDelta / bytesDelta;
    }
    return std::nullopt;
}


std::optional<double> SpeedTest::getBytesPerSec() const
{
    if (!samples_.empty())
    {
        const double timeDelta = std::chrono::duration<double>(samples_.back().timeElapsed - samples_.front().timeElapsed).count();
        const int64_t bytesDelta = samples_.back().bytes - samples_.front().bytes;

        if (!numeric::isNull(timeDelta))
            return bytesDelta / timeDelta;
    }
    return std::nullopt;
}


std::optional<double> SpeedTest::getItemsPerSec() const
{
    if (!samples_.empty())
    {
        const double timeDelta = std::chrono::duration<double>(samples_.back().timeElapsed - samples_.front().timeElapsed).count();
        const int itemsDelta = samples_.back().items - samples_.front().items;

        if (!numeric::isNull(timeDelta))
            return itemsDelta / timeDelta;
    }
    return std::nullopt;
}


std::wstring SpeedTest::getBytesPerSecFmt() const
{
    if (const std::optional<double> bps = getBytesPerSec())
        return replaceCpy(_("%x/sec"), L"%x", formatFilesizeShort(std::llround(*bps)));
    return {};
}


std::wstring SpeedTest::getItemsPerSecFmt() const
{
    if (const std::optional<double> ips = getItemsPerSec())
        return replaceCpy(_("%x/sec"), L"%x", replaceCpy(_("%x items"), L"%x", formatTwoDigitPrecision(*ips)));
    return {};
}


/*
class for calculation of remaining time:
----------------------------------------
"filesize |-> time" is an affine linear function f(x) = z_1 + z_2 x

For given n measurements, sizes x_0, ..., x_n and times f_0, ..., f_n, the function f (as a polynom of degree 1) can be lineary approximated by

z_1 = (r - s * q / p) / ((n + 1) - s * s / p)
z_2 = (q - s * z_1) / p = (r - (n + 1) z_1) / s

with
p := x_0^2 + ... + x_n^2
q := f_0 x_0 + ... + f_n x_n
r := f_0 + ... + f_n
s := x_0 + ... + x_n

=> the time to process N files with amount of data D is:    N * z_1 + D * z_2

Problem:
--------
Times f_0, ..., f_n can be very small so that precision of the PC clock is poor.
=> Times have to be accumulated to enhance precision:
Copying of m files with sizes x_i and times f_i (i = 1, ..., m) takes sum_i f(x_i) := m * z_1 + z_2 * sum x_i = sum f_i
With X defined as the accumulated sizes and F the accumulated times this gives: (in theory...)
m * z_1 + z_2 * X = F   <=>
z_1 + z_2 * X / m = F / m

=> we obtain a new (artificial) measurement with size X / m and time F / m to be used in the linear approximation above


Statistics::Statistics(int totalObjectCount, double totalDataAmount, unsigned recordCount) :
        itemsTotal(totalObjectCount),
        bytesTotal(totalDataAmount),
        recordsMax(recordCount),
        objectsLast(0),
        dataLast(0),
        timeLast(wxGetLocalTimeMillis()),
        z1_current(0),
        z2_current(0),
        dummyRecordPresent(false) {}


wxString Statistics::getRemainingTime(int objectsCurrent, double dataCurrent)
{
    //add new measurement point
    const int m = objectsCurrent - objectsLast;
    if (m != 0)
    {
        objectsLast = objectsCurrent;

        const double X = dataCurrent - dataLast;
        dataLast = dataCurrent;

        const int64_t timeCurrent = wxGetLocalTimeMillis();
        const double F = (timeCurrent - timeLast).ToDouble();
        timeLast = timeCurrent;

        record newEntry;
        newEntry.x_i = X / m;
        newEntry.f_i = F / m;

        //remove dummy record
        if (dummyRecordPresent)
        {
            measurements.pop_back();
            dummyRecordPresent = false;
        }

        //insert new record
        measurements.push_back(newEntry);
        if (measurements.size() > recordsMax)
            measurements.pop_front();
    }
    else //dataCurrent increased without processing new objects:
    {    //modify last measurement until m != 0
        const double X = dataCurrent - dataLast; //do not set dataLast, timeLast variables here, but write dummy record instead
        if (!isNull(X))
        {
            const int64_t timeCurrent = wxGetLocalTimeMillis();
            const double F = (timeCurrent - timeLast).ToDouble();

            record modifyEntry;
            modifyEntry.x_i = X;
            modifyEntry.f_i = F;

            //insert dummy record
            if (!dummyRecordPresent)
            {
                measurements.push_back(modifyEntry);
                if (measurements.size() > recordsMax)
                    measurements.pop_front();
                dummyRecordPresent = true;
            }
            else //modify dummy record
                measurements.back() = modifyEntry;
        }
    }

    //calculate remaining time based on stored measurement points
    double p = 0;
    double q = 0;
    double r = 0;
    double s = 0;
    for (const record& rec : measurements)
    {
        const double x_i = rec.x_i;
        const double f_i = rec.f_i;
        p += x_i * x_i;
        q += f_i * x_i;
        r += f_i;
        s += x_i;
    }

    if (!isNull(p))
    {
        const double n   = measurements.size();
        const double tmp = (n - s * s / p);

        if (!isNull(tmp) && !isNull(s))
        {
            const double z1 = (r - s * q / p) / tmp;
            const double z2 = (r - n * z1) / s;    //not (n + 1) here, since n already is the number of measurements

            //refresh current values for z1, z2
            z1_current = z1;
            z2_current = z2;
        }
    }

    return formatRemainingTime((itemsTotal - objectsCurrent) * z1_current + (bytesTotal - dataCurrent) * z2_current);
}
*/