/***
    Copyright (C) 2022 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: AuIOPipeProcessor.cpp
    Date: 2022-6-6
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include <Aurora/IO/IOExperimental.hpp>
#include "AuIOProcessor.hpp"
#include "AuIOPipeProcessor.hpp"
#include <Aurora/IO/Protocol/Protocol.hpp>

namespace Aurora::IO
{
    IOPipeWork::IOPipeWork(const AuSPtr<IOPipeProcessor> &parent, const IOPipeRequestAIO &request) :
        parent_(parent),
        request(request),
        startCallback(this),
        endCallback(this),
        output(request.output)
    {
        this->uFrameCap_ = request.uPageLengthOrZero ? request.uPageLengthOrZero : request.kFallbackPageSize;
        this->uBufferSize_ = request.uBufferLengthOrZero ? request.uBufferLengthOrZero : request.kFallbackBufferSize;
        this->uBytesWrittenLimit_ = request.uLengthOrZero;
        this->uBytesWrittenTarget_ = request.uMinBytesToRead ? request.uMinBytesToRead : request.uLengthOrZero;
        this->pAsyncTransaction_ = request.pAsyncTransaction;
        this->pAsyncAdapter_ = NewAsyncStreamAdapter(request.pAsyncTransaction, request.bIsStream);
        SysAssert(this->pAsyncAdapter_);
        this->pAsyncAdapter_->SetReadOffset(request.uStartOffset);
        this->pAsyncAdapter_->SetWriteOffset(request.uStartOffset);
        this->pAsyncStreamReader_ = this->pAsyncAdapter_->ToStreamReader();
    }

    IOPipeWork::IOPipeWork(const AuSPtr<IOPipeProcessor> &parent, const IOPipeRequestBasic &request) :
        parent_(parent),
        request(request),
        startCallback(this),
        endCallback(this),
        output(request.output)
    {
        this->uBufferSize_ = request.uBufferLengthOrZero ? request.uBufferLengthOrZero : request.kFallbackBufferSize;
        this->uFrameCap_ = request.uPageLengthOrZero ? request.uPageLengthOrZero : request.kFallbackPageSize;
        this->uBytesWrittenLimit_ = request.uLengthOrZero;
        this->uBytesWrittenTarget_ = request.uMinBytesToRead ? request.uMinBytesToRead : request.uLengthOrZero;
    }

    void IOPipeWork::Tick_FrameEpilogue()
    {
        if (this->bWritingAheadLowLatency)
        {
            this->TryPump();
        }

        if (AuExchange(this->bShouldReadNext, false))
        {
            this->ReadNext();
        }
    }

    void IOPipeWork::Tick_Any()
    {
        if (this->pAsyncTransaction_)
        {
            this->AsyncPump();
        }
        else
        {
            this->StreamPump();
        }
    }

    void IOPipeWork::OnFailureCompletion()
    {
        this->TerminateOnThread(true);
    }

    void IOPipeWork::OnNominalCompletion()
    {
        this->TerminateOnThread();
    }

    ////////////////////////////////////////////////////////////

    IOWorkStart::IOWorkStart(IOPipeWork *parent) : parent(parent)
    {

    }

    void IOWorkStart::OnRun()
    {
        parent->RunOnThread();
    }

    void IOWorkStart::OnCanceled()
    {
        parent->TerminateOnThread();
    }

    ////////////////////////////////////////////////////////////

    IOWorkEnd::IOWorkEnd(IOPipeWork *parent) : parent(parent)
    {

    }

    void IOWorkEnd::OnRun()
    {
        parent->TerminateOnThread();
    }

    void IOWorkEnd::OnCanceled()
    {
        parent->TerminateOnThread();
    }

    ////////////////////////////////////////////////////////////

    bool IOPipeWork::Start()
    {
        AuSPtr<IIOProcessorItem> ret;

        if (this->pAsyncTransaction_)
        {
            auto pWaitable = this->pAsyncAdapter_->ToWaitable();
            if (pWaitable)
            {
                ret = this->parent_->parent_->StartIOWatch(pWaitable, AuSharedFromThis());
                if (!ret)
                {
                    return false;
                }
            }
        }
        else
        {
            ret = this->parent_->parent_->StartIOWatch(this->input_.pWatchItem, AuSharedFromThis());

            if (!ret)
            {
                return false;
            }
        }

        this->pWatch = ret;

        if (this->parent_->parent_->CheckThread())
        {
            RunOnThread();
            return true;
        }

        return this->parent_->
                     parent_->SubmitIOWorkItem(AuSPtr<IIOProcessorWorkUnit>(this->SharedFromThis(),
                                                                            &this->startCallback));
    }

    bool IOPipeWork::End()
    {
        if (this->parent_->parent_->CheckThread())
        {
            TerminateOnThread();
            return true;
        }
        
        return this->parent_->
                     parent_->SubmitIOWorkItem(AuSPtr<IIOProcessorWorkUnit>(this->SharedFromThis(),
                                                                            &this->endCallback));
    }

    AuInt64 IOPipeWork::GetLastTickMS()
    {
        return this->throughput_.GetLastFrameTimeWall();
    }

    AuInt64 IOPipeWork::GetStartTickMS()
    {
        return this->iStartTickMS_;
    }

    double IOPipeWork::GetPredictedThroughput()
    {
        return this->throughput_.GetEstimatedHertz();
    }

    AuUInt64 IOPipeWork::GetBytesProcessed()
    {
        return this->uBytesWritten_;
    }

    AuUInt64 IOPipeWork::GetBytesProcessedInterframe()
    {
        return this->uBytesWritten_ + this->bytesProcessedInterframe_;
    }

    void IOPipeWork::PrepareStream()
    {
        if (!this->buffer_.IsEmpty())
        {
            return;
        }
         
        if (!this->buffer_.Allocate(this->uBufferSize_, AuHwInfo::GetPageSize(), true))
        {
            SysPushErrorMem();
            TerminateOnThread(true);
            return;
        }
    }

    void IOPipeWork::PrepareAsync()
    {
        PrepareStream();
        ReadNext();
    }

    void IOPipeWork::AsyncPump()
    {
        AuMemoryViewWrite internalBuffer;
        
        auto err = this->pAsyncStreamReader_->Dequeue(0, internalBuffer);
        if (err != EStreamError::eErrorNone)
        {
            SysPushErrorIO("Async Stream Error: {}", err);
            TerminateOnThread(true);
            return;
        }

        if (internalBuffer.length == 0)
        {
            // end of stream
            TerminateOnThread(false);
            return;
        }

        err = this->pAsyncStreamReader_->Dequeue(internalBuffer.length, internalBuffer);
        if (err != EStreamError::eErrorNone)
        {
            SysPushErrorIO("Async Stream Error: {}", err);
            TerminateOnThread(true);
            return;
        }

        this->buffer_.writePtr += internalBuffer.length;

        // end of low-latency read-ahead tick
        if (this->bWritingAheadLowLatency)
        {
            // shift if running out of linear space
            auto readHead = this->buffer_.readPtr - this->buffer_.base;
            if (readHead > (this->buffer_.length / 4) * 3)
            {
                auto readPtr = this->buffer_.base + readHead;
                auto len = this->buffer_.writePtr - readPtr;
                AuMemmove(this->buffer_.base, readPtr, len);
                this->buffer_.writePtr = this->buffer_.base + len;
                this->buffer_.readPtr = this->buffer_.base;
            }

            this->bWritingAheadLowLatency = false;
        }
        
        // attempt low-latency read-ahead
        if (!this->bWritingAheadLowLatency &&
            this->buffer_.CanWrite(this->uFrameCap_) /*ensure we can run ahead*/ &&
            !this->IsAtRequestedEnd() /*do not preemptively terminate before the last callback is fired*/)
        {
            this->bWritingAheadLowLatency = true;
            this->ReadNext();
        
            // TryPump is delegated to the frame epilogue so that we can do a batched send of the next frames reads
            // followed by a tick of frame[-1]
        }
        else
        {
            this->TryPump();
        }
    }

    void IOPipeWork::StreamPump()
    {
        AuUInt canBuffer = this->buffer_.RemainingWrite();
        canBuffer = AuMin(canBuffer, AuUInt((this->buffer_.length + this->buffer_.base) - this->buffer_.writePtr));

        AuUInt read {};
        try
        {
            if (this->input_.pReader->Read(AuMemoryViewStreamWrite(AuMemoryViewWrite(this->buffer_.writePtr, canBuffer), read)) !=
                AuIO::EStreamError::eErrorNone)
            {
                TerminateOnThread();
                return;
            }
        }
        catch (...)
        {
            SysPushErrorCatch();
        }

        this->buffer_.writePtr += read;
        if (this->buffer_.writePtr == this->buffer_.base + this->buffer_.length)
        {
            this->buffer_.writePtr = this->buffer_.base;
        }

        TryPump();
    }

    void IOPipeWork::ReadNextAsync()
    {
        try
        {
            AuUInt canBuffer = this->buffer_.RemainingWrite();
            canBuffer = AuMin(canBuffer, AuUInt((this->buffer_.length + this->buffer_.base) - this->buffer_.writePtr));
            canBuffer = AuMin(AuUInt(this->uFrameCap_), canBuffer);

            this->nextWriteAsync_ = AuMemoryViewWrite(this->buffer_.writePtr, canBuffer);

            if (this->pAsyncStreamReader_->BeginRead(AuSPtr<AuMemoryViewWrite>(this->SharedFromThis(), &this->nextWriteAsync_)) !=
                AuIO::EStreamError::eErrorNone)
            {
                if (this->bWritingAheadLowLatency)
                {
                    this->bWritingAheadIOUOneTerminate = true;
                }
                else
                {
                    TerminateOnThread(true);
                }
                return;
            }

            if (!this->nextWriteAsync_)
            {
                TerminateOnThread();
                return;
            }
        }
        catch (...)
        {
            SysPushErrorCatch();
        }
    }

    void IOPipeWork::ReadNext()
    {
        if (!this->bActive)
        {
            return;
        }

        if (IsAtRequestedEnd())
        {
            TerminateOnThread(false);
            return;
        }

        if (this->pAsyncTransaction_)
        {
            ReadNextAsync();
        }
        else
        {
            if (this->input_.pBackend)
            {
                this->input_.pBackend->OnEndPump();
            }
        }
    }

    AuUInt32 IOPipeWork::TryPump()
    {
        AuUInt &bytesProcessedTotal = this->bytesProcessedInterframe_;
        AuUInt bytesProcessed {};
        bool bIsCullingLastFrame {};

        bytesProcessedTotal = 0;

        do
        {
            AuUInt canRead2 = this->buffer_.RemainingBytes();
            AuUInt canRead = canRead2;
            if (!canRead)
            {
                break;
            }

            canRead = AuMin<AuUInt>(canRead, (this->buffer_.length + this->buffer_.base) - this->buffer_.readPtr);
            if (!canRead)
            {
                continue;
            }

            auto oldReadHeadPtr = this->buffer_.readPtr;
            auto readHead = oldReadHeadPtr - this->buffer_.base;

            auto oldWriteHeadPtr = this->buffer_.writePtr;
            auto writeHead = oldWriteHeadPtr - this->buffer_.base;

            auto uInterframeProgress = this->GetBytesProcessedInterframe();
            
            if ((bIsCullingLastFrame = ((this->uBytesWrittenLimit_ && canRead2 + uInterframeProgress > this->uBytesWrittenLimit_))))
            {
                auto uLastFrameBytes = this->uBytesWrittenLimit_ - uInterframeProgress;
                auto uAbsDataToRead = AuMin<AuUInt>(canRead, uLastFrameBytes);
                this->buffer_.writePtr = this->buffer_.readPtr + uAbsDataToRead;
            }

            if (this->pProtocolStack)
            {
                this->pProtocolStack->DoTick();
            }

            try
            {
                if (this->output.type == EPipeCallbackType::eTryHandleBufferedPart)
                {
                    if (this->output.handleBufferedStream.pOnData)
                    {
                        if (!this->output.handleBufferedStream.pOnData->OnDataAvailable(this->buffer_))
                        {
                            bytesProcessed = 0;
                            this->buffer_.readPtr = this->buffer_.base + readHead;
                        }
                        else
                        {
                            bytesProcessed = this->buffer_.readPtr - oldReadHeadPtr;
                        }
                    }
                    else
                    {
                        bytesProcessed = this->buffer_.readPtr - oldReadHeadPtr;
                    }
                }
                else if (this->output.type == EPipeCallbackType::eWriteToWriter)
                {
                    if (this->output.forwardStream.pIntercepter && 
                        this->output.forwardStream.pWriter)
                    {
                        if (!this->output.forwardStream.pIntercepter->OnDataAvailable(AuMemoryViewStreamRead(AuMemoryViewRead(this->buffer_.readPtr, canRead), bytesProcessed), this->output.forwardStream.pWriter))
                        {
                            bytesProcessed = 0;
                        }
                        else
                        {
                            this->buffer_.readPtr += bytesProcessed;
                        }
                    }
                    else
                    {
                        bytesProcessed = this->buffer_.readPtr - oldReadHeadPtr;
                    }
                }
            }
            catch (...)
            {
                SysPushErrorCatch();
            }

            bytesProcessedTotal += bytesProcessed;

            if (!this->bWritingAheadLowLatency)
            {
                if (oldWriteHeadPtr != this->buffer_.writePtr)
                {
                    this->buffer_.writePtr = this->buffer_.base + writeHead;
                }

                if (bIsCullingLastFrame)
                {
                    this->bShouldReadNext = false;
                    break;
                }

                if (this->buffer_.readPtr == this->buffer_.writePtr)
                {
                    this->buffer_.readPtr = this->buffer_.base;
                    this->buffer_.writePtr = this->buffer_.base;

                    this->bShouldReadNext = true;
                }
                else if (!bytesProcessed)
                {
                    this->bShouldReadNext = true;
                }

                // Prevent fucky end of allocation issues by moving the tail end of a partially buffered stream back to the start

                // Should help with packing massive files, where faster disks can spin through smaller frames, leaving
                //  the CPU to catch up towards the end of the buffer, at which point the linearity breaks.
                // We must instead force linearity, and with the assumption we can move peekable memory around, we must eventually
                //  move the tail end of the buffer back to the start, just so we can continue that stream view linearity.

                // I really don't know how ReadNextAsync can be expected to wrap around a ring buffer.
                // We'd need to know if this pass failed, and if the read head is near the end, it'd know to wrap back around to zero.
                // An overengineered pain and liability.

                // This should allow us to continue working in linear space without resorting to circular ring buffers

                {
                    auto readHead = this->buffer_.readPtr - this->buffer_.base;
                    if (readHead > (this->buffer_.length / 4) * 3)
                    {
                        auto readPtr = this->buffer_.base + readHead;
                        auto len = this->buffer_.writePtr - readPtr;
                        AuMemmove(this->buffer_.base, readPtr, len);
                        this->buffer_.writePtr = this->buffer_.base + len;
                        this->buffer_.readPtr = this->buffer_.base;
                    }
                }
            }

            if (this->output.type == EPipeCallbackType::eWriteToWriter)
            {
                if (this->output.forwardStream.bFlushWriter)
                {
                    if (this->output.forwardStream.pWriter)
                    {
                        this->output.forwardStream.pWriter->Flush();
                    }
                }
            }
        }
        while (AuExchange(bytesProcessed, 0));


        if (!this->bWritingAheadLowLatency)
        {
            if (!bIsCullingLastFrame)
            {
                if (this->buffer_.readPtr == this->buffer_.base)
                {
                    this->bShouldReadNext = true;
                }
            }
        }

        this->uBytesWritten_ += bytesProcessedTotal;

        this->throughput_.OnUpdate(bytesProcessedTotal);

        if (this->request.pListener)
        {
            this->request.pListener->OnPipePartialEvent(bytesProcessedTotal);
        }

        if (bIsCullingLastFrame)
        {
            this->TerminateOnThread(false);
        }

        if (this->bWritingAheadIOUOneTerminate)
        {
            this->TerminateOnThread(true);
        }

        return bytesProcessedTotal;
    }

    bool IOPipeWork::IsAtRequestedEnd()
    {
        return this->uBytesWrittenLimit_ && (this->uBytesWrittenLimit_ <= this->uBytesWritten_);
    }

    AuByteBuffer *IOPipeWork::GetBuffer()
    {
        return &this->buffer_;
    }

    void IOPipeWork::RunOnThread()
    {
        if (this->input_.pBackend)
        {
            this->input_.pBackend->OnStart();
        }

        if (this->pAsyncTransaction_)
        {
            PrepareAsync();
        }
        else
        {
            PrepareStream();
        }
    }

    void IOPipeWork::TerminateOnThread(bool error)
    {
        if (!this->bActive)
        {
            return;
        }

        this->bActive = false;

        if (this->output.type == EPipeCallbackType::eWriteToWriter)
        {
            if (this->output.forwardStream.bCloseWriter)
            {
                if (auto pWriter = this->output.forwardStream.pWriter)
                {
                    pWriter->Close();
                }
            }
        }
        

        if (this->pWatch)
        {
            this->pWatch->StopWatch();
        }

        if (this->request.pListener)
        {
            if (error)
            {
                // We explicitly failed...
                this->request.pListener->OnPipeFailureEvent();
            }
            else if (this->uBytesWrittenTarget_ && (this->uBytesWrittenTarget_ > this->uBytesWritten_))
            {
                // Finished without error early
                this->request.pListener->OnPipeFailureEvent();
            }
            else
            {
                // We finished...
                this->request.pListener->OnPipeSuccessEvent();
            }

            this->request.pListener.reset();
        }

        this->output.handleBufferedStream.pOnData.reset();
        this->output.forwardStream.pIntercepter.reset();
        this->output.forwardStream.pWriter.reset();

        if (this->input_.pBackend)
        {
            this->input_.pBackend->OnEnd();
            this->input_.pBackend.reset();
        }

        if (auto transaction = this->pAsyncTransaction_)
        {
            transaction->Reset();
            this->pAsyncTransaction_.reset();
        }

        this->pAsyncAdapter_.reset();
        this->pAsyncStreamReader_.reset();

        if (this->pProtocolStack)
        {
            this->pProtocolStack->Destroy();
            this->pProtocolStack.reset();
        }

        this->PrivateUserDataClear();
    }

    IOPipeProcessor::IOPipeProcessor(IOProcessor *parent) :
        parent_(parent)
    {

    }

    AuSPtr<IIOPipeWork> IOPipeProcessor::NewBasicPipe(const IOPipeRequestBasic &request)
    {
        // TODO: Incomplete
        return AuMakeShared<IOPipeWork>(AuStaticCast<IOPipeProcessor>(this->parent_->ToPipeProcessor()), request);
    }

    AuSPtr<IIOPipeWork> IOPipeProcessor::NewAIOPipe(const IOPipeRequestAIO &request)
    {
        // TODO: Incomplete
        return AuMakeShared<IOPipeWork>(AuStaticCast<IOPipeProcessor>(this->parent_->ToPipeProcessor()), request);
    }
}