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

    File: AuRWLock.cpp
    Date: 2021-6-12
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "AuRWLock.hpp"

namespace Aurora::Threading::Primitives
{
    template<bool bIsReadView, typename T>
    void RWLockAccessView<bIsReadView, T>::Unlock()
    {
        if constexpr (bIsReadView)
        {
            this->parent_.UnlockRead();
        }
        else
        {
            this->parent_.UnlockWrite();
        }
    }

    template<bool bIsReadView, typename T>
    bool RWLockAccessView<bIsReadView, T>::Lock(AuUInt64 timeout)
    {
        if constexpr (bIsReadView)
        {
            return this->parent_.LockReadNS(AuMSToNS<AuUInt64>(timeout));
        }
        else
        {
            return this->parent_.LockWriteNS(AuMSToNS<AuUInt64>(timeout));
        }
    }


    template<bool bIsReadView, typename T>
    bool RWLockAccessView<bIsReadView, T>::LockNS(AuUInt64 timeout)
    {
        if constexpr (bIsReadView)
        {
            return this->parent_.LockReadNS(timeout);
        }
        else
        {
            return this->parent_.LockWriteNS(timeout);
        }
    }

    template<bool bIsReadView, typename T>
    bool RWLockAccessView<bIsReadView, T>::TryLock()
    {
        if constexpr (bIsReadView)
        {
            return this->parent_.TryLockRead();
        }
        else
        {
            return this->parent_.TryLockWrite();
        }
    }

    template<bool bIsWriteRecursionAllowed>
    RWLockImpl<bIsWriteRecursionAllowed>::RWLockImpl() :
        read_(*this),
        write_(*this),
        condition_(AuUnsafeRaiiToShared(&this->mutex_))
    {

    }

    template<bool bIsWriteRecursionAllowed>
    RWLockImpl<bIsWriteRecursionAllowed>::~RWLockImpl()
    {
    }

    template<bool bIsWriteRecursionAllowed>
    bool RWLockImpl<bIsWriteRecursionAllowed>::Init()
    {
        return true;
    }
        
    template<bool bIsWriteRecursionAllowed>
    bool RWLockImpl<bIsWriteRecursionAllowed>::LockReadNS(AuUInt64 uTimeout)
    {
        if (this->state_ < 0 &&
            this->reentrantWriteLockHandle_ == AuThreads::GetThreadId())
        {
            return true;
        }

        AuInt64 uEndTime = uTimeout ? AuTime::SteadyClockNS() + uTimeout : 0;

        AuInt32 iCurState {};
        do
        {
            iCurState = this->state_;

            if (iCurState < 0)
            {
                AU_LOCK_GUARD(this->mutex_);

                iCurState = this->state_;
                if (iCurState < 0)
                {
                    AuInt64 uSecondTimeout = 0;

                    if (uTimeout)
                    {
                        uSecondTimeout = uEndTime - AuTime::SteadyClockNS();

                        if (uSecondTimeout <= 0)
                        {
                            return false;
                        }

                        uSecondTimeout = AuNSToMS<AuUInt64>(uSecondTimeout);
                        if (!uSecondTimeout)
                        {
                            return false;
                        }
                    }

                    if (!this->condition_.WaitForSignal(uSecondTimeout))
                    {
                        return false;
                    }

                    if (this->writersPending_)
                    {
                        this->condition_.Broadcast();
                        continue;
                    }
                }
            }
        }
        while (iCurState < 0 ||
               AuAtomicCompareExchange(&this->state_, iCurState + 1, iCurState) != iCurState);

        return true;
    }

    template<bool bIsWriteRecursionAllowed>
    bool RWLockImpl<bIsWriteRecursionAllowed>::LockWriteNS(AuUInt64 uTimeout)
    {
        if constexpr (!bIsWriteRecursionAllowed)
        {
            if (TryLockWrite())
            {
                return true;
            }
        }
        else
        {
            auto uOld = this->state_;
            if (uOld < 0)
            {
                if (this->reentrantWriteLockHandle_ == AuThreads::GetThreadId())
                {
                    AuAtomicSub(&this->state_, 1);
                    return true;
                }
            }
            else if (uOld == 0)
            {
                if (AuAtomicCompareExchange(&this->state_, -1, uOld) == uOld)
                {
                    this->reentrantWriteLockHandle_ = AuThreads::GetThreadId();
                    return true;
                }
            }
        }

        AU_LOCK_GUARD(this->mutex_);
        this->writersPending_++;

        AuInt64 uEndTime = uTimeout ? AuTime::SteadyClockNS() + uTimeout : 0;

        while (true)
        {
            while (this->state_ != 0)
            {
                AuInt64 uSecondTimeout = 0;

                if (uTimeout)
                {
                    uSecondTimeout = uEndTime - AuTime::SteadyClockNS();

                    if (uSecondTimeout <= 0)
                    {
                        this->writersPending_--;
                        return false;
                    }

                    uSecondTimeout = AuNSToMS<AuUInt64>(uSecondTimeout);
                    if (!uSecondTimeout)
                    {
                        this->writersPending_--;
                        return false;
                    }
                }

                if (!this->condition_.WaitForSignal(uSecondTimeout))
                {
                    this->writersPending_--;
                    return false;
                }
            }

            if (AuAtomicCompareExchange(&this->state_, -1, 0) == 0)
            {
                this->reentrantWriteLockHandle_ = AuThreads::GetThreadId();
                this->writersPending_--;
                return true;
            }
        }

        return true;
    }
    
    template<bool bIsWriteRecursionAllowed>
    bool RWLockImpl<bIsWriteRecursionAllowed>::TryLockRead()
    {
        auto iCurState = this->state_;

        if (iCurState == -1)
        {
            return this->reentrantWriteLockHandle_ == AuThreads::GetThreadId();
        }

        return AuAtomicCompareExchange(&this->state_, iCurState + 1, iCurState) == iCurState;
    }

    template<bool bIsWriteRecursionAllowed>
    bool RWLockImpl<bIsWriteRecursionAllowed>::TryLockWrite()
    {
        for (AuUInt i = 0; i < 20; i++)
        {
            auto curVal = this->state_;

            if (curVal < 0)
            {
                if constexpr (!bIsWriteRecursionAllowed)
                {
                    AuThreading::ContextYield();
                    continue;
                }
                else
                {
                    if (this->reentrantWriteLockHandle_ == AuThreads::GetThreadId())
                    {
                        AuAtomicSub(&this->state_, 1);
                        return true;
                    }
                    else
                    {
                        AuThreading::ContextYield();
                        continue;
                    }
                }
            }

            if (curVal != 0)
            {
                continue;
            }

            if (AuAtomicCompareExchange(&this->state_, -1, curVal) == curVal)
            {
                this->reentrantWriteLockHandle_ = AuThreads::GetThreadId();
                return true;
            }
        }

        return false;
    }
    
    template<bool bIsWriteRecursionAllowed>
    void RWLockImpl<bIsWriteRecursionAllowed>::UnlockRead()
    {
        if (this->state_ < 0)
        {
            SysAssertDbg(this->reentrantWriteLockHandle_ == AuThreads::GetThreadId());
            return;
        }

        AU_LOCK_GUARD(this->mutex_);

        auto val = AuAtomicSub(&this->state_, 1);
        
        if ((val == 1) && (this->bElevaterPending_))
        {
            this->condition_.Signal();
        }

        if (val == 0)
        {
            this->condition_.Signal();
        }
    }

    template<bool bIsWriteRecursionAllowed>
    void RWLockImpl<bIsWriteRecursionAllowed>::UnlockWrite()
    {
        AU_LOCK_GUARD(this->mutex_);

        if constexpr (!bIsWriteRecursionAllowed)
        {
            this->reentrantWriteLockHandle_ = 0;
            this->state_ = 0;
            this->condition_.Broadcast();
        }
        else
        {
            if (AuAtomicAdd(&this->state_, 1) == 0)
            {
                this->reentrantWriteLockHandle_ = 0;
                this->condition_.Broadcast();
            }
        }
    }
    
    template<bool bIsWriteRecursionAllowed>
    bool RWLockImpl<bIsWriteRecursionAllowed>::UpgradeReadToWrite(AuUInt64 timeout)
    {
        AU_LOCK_GUARD(this->mutex_);
    
        while (this->state_ != 1)
        {
            this->bElevaterPending_ = true;

            if (!this->condition_.WaitForSignal(timeout))
            {
                return false;
            }
        }
        
        this->bElevaterPending_ = false;
        this->reentrantWriteLockHandle_ = AuThreads::GetThreadId();
        this->state_ = -1;
        return true;
    }

    template<bool bIsWriteRecursionAllowed>
    bool RWLockImpl<bIsWriteRecursionAllowed>::DowngradeWriteToRead()
    {
        AU_LOCK_GUARD(this->mutex_);

        if (this->state_ != -1)
        {
            return false;
        }

        this->state_ = 1;
        this->condition_.Broadcast();
        return true;
    }

    template<bool bIsWriteRecursionAllowed>
    IWaitable *RWLockImpl<bIsWriteRecursionAllowed>::AsReadable()
    {
        return &this->read_;
    }
    template<bool bIsWriteRecursionAllowed>
    IWaitable *RWLockImpl<bIsWriteRecursionAllowed>::AsWritable()
    {
        return &this->write_;
    }

    AUKN_SYM IRWLock *RWLockNew()
    {
        auto pRwLock = _new RWLockImpl<false>();
        if (!pRwLock)
        {
            return nullptr;
        }

        if (!pRwLock->Init())
        {
            delete pRwLock;
            return nullptr;
        }

        return pRwLock;
    }

    AUKN_SYM void RWLockRelease(IRWLock *pRwLock)
    {
        AuSafeDelete<RWLockImpl<false> *>(pRwLock);
    }

    AUKN_SYM IRWLock *RWRenterableLockNew()
    {
        auto pRwLock = _new RWLockImpl<true>();
        if (!pRwLock)
        {
            return nullptr;
        }

        if (!pRwLock->Init())
        {
            delete pRwLock;
            return nullptr;
        }

        return pRwLock;
    }

    AUKN_SYM void RWRenterableLockRelease(IRWLock *pRwLock)
    {
        AuSafeDelete<RWLockImpl<true> *>(pRwLock);
    }
}