/***
    Copyright (C) 2021-2024 Jamie Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: LSTimerNoKernelScheduler.cpp
    Date: 2024-09-08
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include <Source/Async/IAsyncRunnable.hpp>
#include <Source/Async/AuSchedular.hpp>
#include "LSTimerNoKernelScheduler.hpp"
#include <Source/Threading/Primitives/SMTYield.hpp>

namespace Aurora::IO::Loop
{
    void LSTimerIPDispatcher::RunAsync()
    {
        AU_LOCK_GUARD(this->mutex);

        // TODO: not as optimized
        // TODO: we now just added a AuSharedFromThis requirement for no good reason
        if (auto pThat = AuTryLockMemoryType(this->pParent))
        {
            pThat->Set();
        }
    }

    LSTimerIP::LSTimerIP(AuUInt32 reschedStepMsOrZero, AuUInt32 maxIterationsOrZero, bool bSingleshot) :
        bSingleshot(bSingleshot),
        reschedStepNsOrZero_(AuMSToNS<AuUInt64>(reschedStepMsOrZero)),
        maxIterationsOrZero_(maxIterationsOrZero)
    {
        this->targetTime_ = AuTime::SteadyClockNS();
    }

    LSTimerIP::~LSTimerIP()
    {
      
    }

    void LSTimerIP::UpdateTimeWall(AuUInt64 absTimeMs)
    {
        this->UpdateTimeWallNs(AuMSToNS<AuUInt64>(absTimeMs));
    }

    void LSTimerIP::UpdateTimeWallNs(AuUInt64 absTimeNs)
    {
        this->UpdateTimeSteadyNs(absTimeNs - AuTime::CurrentClockNS() + AuTime::SteadyClockNS());
    }

    void LSTimerIP::UpdateTimeSteady(AuUInt64 absTimeMs)
    {
        this->UpdateTimeSteadyNs(AuMSToNS<AuUInt64>(absTimeMs));
    }

    void LSTimerIP::UpdateTickRateIfAny(AuUInt32 reschedStepMsOrZero, AuUInt32 maxIterationsOrZero)
    {
        this->UpdateTickRateIfAnyNs(AuMSToNS<AuUInt64>(reschedStepMsOrZero), maxIterationsOrZero);
    }

    void LSTimerIP::UpdateTickRateIfAnyNs(AuUInt64 reschedStepNsOrZero, AuUInt32 maxIterationsOrZero)
    {
        AU_LOCK_GUARD(this->cs);

        this->Stop();

        this->reschedStepNsOrZero_ = reschedStepNsOrZero;
        this->maxIterationsOrZero_ = maxIterationsOrZero;
        this->count_ = 0;

        if (this->targetTime_)
        {
            this->UpdateTimeSteadyNs(this->targetTime_);
        }
    }

    void LSTimerIP::UpdateTimeSteadyNs(AuUInt64 absTimeNs)
    {
        AU_DEBUG_MEMCRUNCH;
        AU_LOCK_GUARD(this->cs);
        
        if (this->pDispatcher)
        {
            AU_LOCK_GUARD(this->pDispatcher->mutex);
            AuResetMember(this->pDispatcher->pParent);
        }
   
        // TODO: optimization was removed. readd it.
        auto pNext = this->pDispatcher = AuMakeShared<LSTimerIPDispatcher>();
        SysAssert(pNext, "impossible OOM during timer op");

        pNext->pParent = this->SharedFromThis();;
        AuAsync::Schedule(absTimeNs, nullptr, {}, pNext);
        this->targetTime_ = absTimeNs;
    }

    void LSTimerIP::Stop()
    {
        AU_LOCK_GUARD(this->cs);

        if (this->pDispatcher)
        {
            AU_LOCK_GUARD(this->pDispatcher->mutex);
            AuResetMember(this->pDispatcher->pParent);
            this->pDispatcher = nullptr;
        }
    }

    bool LSTimerIP::IsSignaledNonblocking()
    {
        AU_LOCK_GUARD(this->cs);

        auto uCurrentTime    = AuTime::SteadyClockNS();
        auto uNextTickTarget = AuAtomicLoad(&this->targetTime_);

        if (uCurrentTime < uNextTickTarget)
        {
            return false;
        }

        auto uNextTick = uNextTickTarget + this->reschedStepNsOrZero_;

        if (uCurrentTime > uNextTick)
        {
            this->targetTime_ = uCurrentTime;
            uNextTick         = uCurrentTime + this->reschedStepNsOrZero_;
        }

        if (!this->maxIterationsOrZero_)
        {
            this->UpdateTimeSteadyNs(uNextTick);
            return true;
        }

        if (AuAtomicAdd<AuUInt32>(&this->count_, 1) <= this->maxIterationsOrZero_)
        {
            this->UpdateTimeSteadyNs(uNextTick);
            return true;
        }
        else
        {
            Stop();
            return false;
        }
    }

    bool LSTimerIP::OnTrigger(AuUInt handle)
    {
        return IsSignaledNoSpinIfUserland();
        return true;
    }

    bool LSTimerIP::TryTakeWaitNS(AuUInt64 uTimeoutAbs)
    {
        auto uNextTime = AuAtomicLoad(&this->targetTime_);

        if (!uNextTime)
        {
            return false;
        }

        if (this->IsSignaledNonblocking())
        {
            return true;
        }
        else
        {
            uNextTime = AuAtomicLoad(&this->targetTime_);
        }

        auto uNow = AuTime::SteadyClockNS();
        if (uNow >= uNextTime)
        {
            return this->IsSignaledNonblocking();
        }

        // TODO: this added mess isn't even hit.

        // Win32 note: there is quite a bit of hackery behind SleepNs
        // Win 7 and lower may spin for a bit
        // Various CPUs may enter a user-space montior condition
        // Dumb CPUs will SMT yield
        // Alderlake et al can tpause
        if (uTimeoutAbs)
        {
            if (uTimeoutAbs < uNextTime)
            {
                AuThreading::SleepNs(uTimeoutAbs - uNow);
                return false;
            }

            AuThreading::SleepNs(uNextTime - uNow);

            while (uNextTime < AuTime::SteadyClockNS())
            {
                if (this->IsSignaledNonblocking())
                {
                    return true;
                }
            }

            return this->IsSignaledNonblocking();
        }
        else
        {
            AuThreading::SleepNs(uNextTime - uNow);
            if (this->IsSignaledNonblocking())
            {
                return true;
            }

            while (AuAtomicLoad(&this->targetTime_) < AuTime::SteadyClockNS())
            {
                if (this->IsSignaledNonblocking())
                {
                    return true;
                }
            }
        }

        return false;
    }

    ELoopSource LSTimerIP::GetType()
    {
        return ELoopSource::eSourceTimer;
    }

    bool LSTimerIP::TryInit()
    {
        return LSEvent::TryInit(false, true, true);
    }

    bool LSTimerIP::IsSignaled()
    {
        return this->TryTakeSpin();
    }

    bool LSTimerIP::IsSignaledNoSpinIfUserland()
    {
        return this->IsSignaledNonblocking();
    }

    bool LSTimerIP::TryTakeNoSpin()
    {
        return this->IsSignaledNonblocking();
    }

    bool LSTimerIP::TryTakeSpin()
    {
        return Threading::Primitives::DoTryIf([&]
        {
            return this->TryTakeNoSpin();
        });
    }

    bool LSTimerIP::TryTake()
    {
        return this->TryTakeSpin();
    }

    AuSPtr<ITimer> NewLSTimerIP(AuUInt64 qwAbsStartTimeMs, AuUInt32 dwReschedStepMsOrZero, AuUInt32 dwMaxIterationsOrZero, bool bSingleshot, bool bIsStartTimeSteady)
    {
        AuAsync::StartSched2();

        auto pTimer = AuMakeShared<LSTimerIP>(dwReschedStepMsOrZero, dwMaxIterationsOrZero, bSingleshot);
        if (!pTimer)
        {
            SysPushErrorMem();
            return {};
        }

        if (!pTimer->TryInit())
        {
            SysPushErrorMem();
            return {};
        }

        if (qwAbsStartTimeMs)
        {
            if (bIsStartTimeSteady)
            {
                pTimer->UpdateTimeSteady(qwAbsStartTimeMs);
            }
            else
            {
                pTimer->UpdateTimeWall(qwAbsStartTimeMs);
            }
        }

        return pTimer;
    }
}