/*
 * Copyright 2009, Ingo Weinhold, ingo_weinhold@gmx.de.
 * Distributed under the terms of the MIT License.
 */
#include "TimeComputer.h"

#include <OS.h>


TimeComputer::TimeComputer()
        :
        fRealTime(0),
        fPerformanceTime(0),
        fDrift(1),
        fFrameRate(1000000),
        fUsecsPerFrame(1),
        fPerformanceTimeBase(0),
        fFrameBase(0),
        fResetTimeBase(true),
        fFirstEntry(0),
        fLastEntry(0)
{
}


void
TimeComputer::Init(float frameRate, bigtime_t realBaseTime)
{
        fRealTime = realBaseTime;
        fPerformanceTime = 0;
        fDrift = 1;
        SetFrameRate(frameRate);
}


void
TimeComputer::SetFrameRate(float frameRate)
{
        if (frameRate == fFrameRate)
                return;

        fFrameRate = frameRate;
        fUsecsPerFrame = (double)1000000 / fFrameRate;
        fResetTimeBase = true;
        fFirstEntry = 0;
        fLastEntry = 0;
}


void
TimeComputer::AddTimeStamp(bigtime_t realTime, uint64 frames)
{
        bigtime_t estimatedPerformanceTime = fPerformanceTime
                + bigtime_t((realTime - fRealTime) * fDrift);

        fRealTime = realTime;

        if (fResetTimeBase) {
                // use the extrapolated performance time at the given real time
                fPerformanceTime = estimatedPerformanceTime;
                fPerformanceTimeBase = estimatedPerformanceTime;
                fFrameBase = frames;
                fResetTimeBase = false;
                _AddEntry(fRealTime, fPerformanceTime);
                fFirstEntry = fLastEntry;
                return;
        }

        // add entry
        bigtime_t performanceTime = fPerformanceTimeBase
                + bigtime_t((frames - fFrameBase) * fUsecsPerFrame);
        _AddEntry(realTime, performanceTime);

        // Update performance time and drift. We don't use the given
        // performance time directly, but average it with the estimated
        // performance time.
        fPerformanceTime = (performanceTime + estimatedPerformanceTime) / 2;

        Entry& entry = fEntries[fFirstEntry];
        fDrift = double(fPerformanceTime - entry.performanceTime)
                / double(fRealTime - entry.realTime);
}


void
TimeComputer::_AddEntry(bigtime_t realTime, bigtime_t performanceTime)
{
        fLastEntry = (fLastEntry + 1) % kEntryCount;
        Entry& entry = fEntries[fLastEntry];
        entry.realTime = realTime;
        entry.performanceTime = performanceTime;

        if (fLastEntry == fFirstEntry)
                fFirstEntry = (fFirstEntry + 1) % kEntryCount;
}