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

    File: Schedular.cpp
    Date: 2021-6-26
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "Async.hpp"
#include "Schedular.hpp"
//#include "AsyncApp.hpp"
#include "ThreadPool.hpp"
#include <Console/Commands/Commands.hpp>

namespace Aurora::Async
{
    struct SchedEntry
    {
        AuUInt64 ns;
        WorkerId_t target;
        AuSPtr<IAsyncRunnable> runnable;
        IThreadPoolInternal *pool;
    };

    // sched thread threading:
    static AuThreads::ThreadUnique_t gThread;
    static AuThreadPrimitives::ConditionMutex gSchedLock;
    static AuThreadPrimitives::ConditionVariable gSchedCondvar(AuUnsafeRaiiToShared(gSchedLock.AsPointer()));

    // next tick timing:
    static AuUInt64 uNextSysTickGuessed {};
    static AuUInt64 uNextWakeuptimeRateLimit {};
    static AuBST<AuUInt64, SchedEntry> gOrderedEntries;
    // prevents stupid tick issues
    static bool gLockedPump = false;
    
    // old sewage to be cleaned up
    static bool gBOriginal;
    static AuOptionalEx<AuWorkerPId_t> gMainThread;
    void StartSched2();
    static void SchedNextTime(AuUInt64 uNSAbs);

    static void GetDispatchableTasks(AuList<SchedEntry> &pending)
    {
        auto time = Time::SteadyClockNS();

        for (auto itr = gOrderedEntries.begin(); itr != gOrderedEntries.end(); )
        {
            auto &[ns, entry] = *itr;

            if (ns > time)
            {
                break;
            }

            if (!AuTryInsert(pending, AuMove(entry)))
            {
                SchedNextTime(time + AuMSToNS<AuUInt64>(3));
                break;
            }

            itr = gOrderedEntries.erase(itr);
        }
    }

    static void PumpSysThread()
    {
        try
        {
            RuntimeSysPump();
        }
        catch (...)
        {
            SysPushErrorCatch("SysPump failed");
        }

        gLockedPump = false;
    }

    static void SchedNextTime(AuUInt64 uNSAbs)
    {
        bool bForceWakeup {};

        if (uNextSysTickGuessed > uNSAbs ||
            !uNextSysTickGuessed)
        {
            while (true)
            {
                auto uCurrent = uNextSysTickGuessed;
                
                if (uCurrent &&
                    uCurrent <= uNSAbs)
                {
                    break;
                }

                if (uNextWakeuptimeRateLimit > uNSAbs)
                {
                    uNSAbs = uNextWakeuptimeRateLimit;
                }

                if (!uCurrent)
                {
                    bForceWakeup = true;
                }

                if (AuAtomicCompareExchange(&uNextSysTickGuessed, uNSAbs, uCurrent) == uCurrent)
                {
                    break;
                }
            }

            if (bForceWakeup)
            {
                gSchedCondvar->Signal();
            }
        }
    }

    static void SchedThread()
    {
        Aurora::Utility::RateLimiter limiter(AuMSToNS<AuUInt64>(gRuntimeConfig.async.dwLegacyMainThreadSystemTickMS));

        // Intentional: no Dec used on this thread; we should never run out of memory to schedule tasks
        AuDebug::AddMemoryCrunch();

        while (AuIsThreadRunning())
        {
            AuList<SchedEntry> pending;

            {
                AU_LOCK_GUARD(gSchedLock);

                auto uNextTick = uNextSysTickGuessed;
                auto uNow = AuTime::SteadyClockNS();

                if (uNow < uNextTick)
                {
                    gSchedCondvar->WaitForSignalNS(uNextTick - uNow);
                }
                else if (uNow == uNextTick)
                {
                    uNextSysTickGuessed = 0;
                }
                else
                {
                    uNextSysTickGuessed = 0;
                    gSchedCondvar->WaitForSignalNS(gRuntimeConfig.async.bEnableLegacyTicks ?
                                                   AuMSToNS<AuUInt64>(gRuntimeConfig.async.dwLegacyMainThreadSystemTickMS) :
                                                   0);
                }

                GetDispatchableTasks(pending);

                uNextWakeuptimeRateLimit = AuTime::SteadyClockNS() + AuMSToNS<AuUInt64>(gRuntimeConfig.async.dwSchedulerRateLimitMS);
            }

            for (auto &entry : pending)
            {
                try
                {
                    AuStaticCast<AuAsync::ThreadPool>(entry.pool)->Run(entry.target, entry.runnable, false);
                }
                catch (...)
                {
                    Debug::PrintError();
                }
            }

            if (gRuntimeConfig.async.bEnableLegacyTicks)
            {
                if (limiter.CheckExchangePass())
                {
                    if (!AuExchange(gLockedPump, true))
                    {
                        DispatchOn(gMainThread.value(), PumpSysThread);
                    }
              
                    SchedNextTime(AuMSToNS<AuUInt64>(gRuntimeConfig.async.dwLegacyMainThreadSystemTickMS) + AuTime::SteadyClockNS());
                }
            }
        }
    }

    void InitSched()
    {

    }

    void DeinitSched()
    {
        if (gThread)
        {
            gThread->SendExitSignal();
        }
        gSchedCondvar->Broadcast();
        gThread.reset();
    }

    AUKN_SYM void SetMainThreadForSysPumpScheduling(AuWorkerPId_t pid)
    {
        if (!pid.pool)
        {
            gRuntimeConfig.async.bEnableLegacyTicks = gBOriginal;
            AuResetMember(gMainThread);
            Console::Commands::UpdateDispatcher(gMainThread);
            return;
        }

        gMainThread = pid;
        Console::Commands::UpdateDispatcher(gMainThread);
        gRuntimeConfig.async.bEnableLegacyTicks = true;

        StartSched2();
    }

    void StartSched()
    {
        if (!gRuntimeConfig.async.bStartSchedularOnStartup)
        {
            return;
        }
        else
        {
            if (gRuntimeConfig.async.dwLegacyMainThreadSystemTickMS && !gMainThread)
            {
                gMainThread = AuWorkerPId_t(AuAsync::GetSharedAsyncApp(), AuWorkerId_t {0, 0});
            }
        }

        StartSched2();
    }

    void StartSched2()
    {
        AU_LOCK_GUARD(gSchedLock);

        if (gThread) return;

        gBOriginal = gRuntimeConfig.async.bEnableLegacyTicks;

        gThread = AuThreads::ThreadUnique(AuThreads::ThreadInfo(
            AuMakeShared<AuThreads::IThreadVectorsFunctional>(AuThreads::IThreadVectorsFunctional::OnEntry_t(std::bind(SchedThread)),
            AuThreads::IThreadVectorsFunctional::OnExit_t {})
        ));

        gThread->Run();
    }
  
    bool Schedule(AuUInt64 ns, IThreadPoolInternal *pool,
                  WorkerId_t target,
                  AuSPtr<IAsyncRunnable> runnable)
    {
        AU_LOCK_GUARD(gSchedLock);
        AU_DEBUG_MEMCRUNCH;
        AuAtomicAdd(&pool->uAtomicCounter, 1u);
        SchedNextTime(ns);
        return AuTryInsert(gOrderedEntries,
                           AuConstReference(ns),
                           SchedEntry { ns, target, runnable, pool });
    }

    void TerminateSceduledTasks(IThreadPoolInternal *pool,
                                WorkerId_t target)
    {
        AU_LOCK_GUARD(gSchedLock);

        for (auto itr = gOrderedEntries.begin(); itr != gOrderedEntries.end(); )
        {
            auto &[ns, entry] = *itr;

            if ((entry.pool == pool) &&
                ((entry.target == target) || 
                (target.second == Async::kThreadIdAny && target.first == entry.target.first)))
            {
                entry.runnable->CancelAsync();
                itr = gOrderedEntries.erase(itr);
            }
            else
            {
                itr ++;
            }
        }
    }
}