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

    File: AsyncApp.cpp
    Date: 2021-6-26
    Author: Reece
***/
#include <RuntimeInternal.hpp>
#include "Async.hpp"
#include "AsyncApp.hpp"
#include "WorkItem.hpp"

namespace Aurora::Async
{
    static AsyncApp gAsyncApp;
    static std::atomic_int gRunningTasks {};

    void IncRunningTasks()
    {
        gRunningTasks++;
    }

    void DecRunningTasks()
    {
        if ((--gRunningTasks) == 0)
        {
            gAsyncApp.ShutdownOutOfTasks();
        }
    }
    
    //STATIC_TLS(WorkerId_t, tlsWorkerId);
    static Threading::Threads::TLSVariable<WorkerId_t, true> tlsWorkerId;

    struct ThreadState
    {
        WorkerId_t id;

        AuUInt8 multipopCount = 1;
        AuUInt32 lastFrameTime {};
        
        Threading::Threads::ThreadShared_t threadObject;

        AuWPtr<GroupState> parent;
    
        Threading::Primitives::SemaphoreUnique_t syncSema;
        AuList<AuSPtr<Threading::Threads::IThreadFeature>> features;

        bool rejecting {};
        bool exiting {};
        
        Threading::Primitives::EventUnique_t running;
        //bool running;
        
        bool inline IsSysThread()
        {
            return id.first == 0;
        }

        AuList<AuSPtr<IAsyncRunnable>> pendingWorkItems;
    };

    struct GroupState
    {
        ThreadGroup_t group;

        Threading::Primitives::ConditionMutexUnique_t    cvWorkMutex;
        Threading::Primitives::ConditionVariableUnique_t cvVariable;

        using WorkEntry_t = std::pair<std::optional<ThreadId_t>, AuSPtr<IAsyncRunnable>>;
        AuList<WorkEntry_t> workQueue;
        
        AuBST<ThreadId_t, AuSPtr<ThreadState>> workers;

        bool Init();

        bool inline IsSysThread()
        {
            return group == 0;
        }
    };

    bool GroupState::Init()
    {
        cvWorkMutex = Threading::Primitives::ConditionMutexUnique();
        if (!cvWorkMutex)
        {
            return false;
        }
        
        cvVariable = Threading::Primitives::ConditionVariableUnique(cvWorkMutex.get());
        if (!cvVariable)
        {
            return false;
        }
        return true;
    }
    
    AsyncApp::AsyncApp()
    {
        rwlock_ = Threading::Primitives::RWLockUnique();
        SysAssert(static_cast<bool>(rwlock_), "Couldn't initialize AsyncApp. Unable to allocate an RWLock");
    }

    // TODO: barrier multiple
    bool AsyncApp::Barrier(WorkerId_t worker, AuUInt32 ms, bool requireSignal, bool drop)
    {
        auto & semaphore = GetThreadState()->syncSema;
        auto unsafeSemaphore = semaphore.get();

        auto work = std::make_shared</*Async::BasicWorkStdFunc*/AsyncFuncRunnable>(([=]()
        {
            auto state = GetThreadState();

            if (drop)
            {
                state->rejecting = true;
            }

            if (requireSignal)
            {
                state->running->Reset();
            }

            unsafeSemaphore->Unlock(1);
        }));
        
    #if 0
        NewWorkItem({worker.first, worker.second}, work)->Dispatch();
    #else
        Run(worker, work);
    #endif

        return WaitFor(worker, semaphore.get(), ms);
    }

    void AsyncApp::Run(DispatchTarget_t target, AuSPtr<IAsyncRunnable> runnable)
    {
        auto state = GetGroup(target.first);
        SysAssert(static_cast<bool>(state), "couldn't dispatch a task to an offline group");
        
        gRunningTasks++;

        {
            Threading::LockGuardPtr lol(state->cvWorkMutex);
            
            #if defined(INTERNAL) || defined(DEBUG)
            Threading::LockGuardPtr lock(rwlock_->AsReadable());

            if (target.second.has_value())
            {
                if (state->workers[*target.second]->rejecting)
                {
                    SysPushErrorGen("worker: {}:{} is offline", target.first, target.second.value_or(0));
                    throw "Requested job worker is offline";
                }
            }
            else
            {
                auto workers = state->workers;
                bool found = false;
                
                for (const auto &worker : state->workers)
                {
                    if (!worker.second->rejecting)
                    {
                        found = true;
                        break;
                    }
                }

                if (!found)
                {
                    throw "No workers available";
                }
            }
            #endif

            state->workQueue.push_back(std::make_pair(target.second, runnable));
        }

        if (target.second.has_value())
        {
            // sad :(
            state->cvVariable->Broadcast();
        }
        else
        {
            state->cvVariable->Signal();
        }
    }

    bool AsyncApp::Poll(bool blocking)
    {
        auto state = GetThreadState();
        auto group = state->parent.lock();

        state->pendingWorkItems.clear();

        {
            Threading::LockGuardPtr lol(group->cvWorkMutex);

            do
            {
                for (auto itr = group->workQueue.begin(); 
                     ((itr != group->workQueue.end()) && 
                      (state->pendingWorkItems.size() < state->multipopCount));
                     )
                {
                    if (!itr->first.has_value())
                    {
                        state->pendingWorkItems.push_back((*itr).second);
                        itr = group->workQueue.erase(itr);
                        continue;
                    }

                    if ((itr->first.has_value()) && (itr->first.value() == state->id.second))
                    {
                        state->pendingWorkItems.push_back((*itr).second);
                        itr = group->workQueue.erase(itr);
                        continue;
                    }

                    itr++;
                }

                if (!blocking)
                {
                    break;
                }

                if (state->pendingWorkItems.empty())
                {
                    group->cvVariable->WaitForSignal();
                }

            } while (state->pendingWorkItems.empty());
        }

        if (state->pendingWorkItems.empty())
        {
            return false;
        }

        int runningTasks {};

        for (auto itr = state->pendingWorkItems.begin(); itr != state->pendingWorkItems.end(); )
        {
            // TODO: we should be able to implement a watchdog later down the line 
            state->lastFrameTime = Time::CurrentClockMS();
            (*itr)->RunAsync();
            itr = state->pendingWorkItems.erase(itr);
            runningTasks = --gRunningTasks;
        }

        if (runningTasks == 0)
        {
            ShutdownOutOfTasks();
        }

        return true;
    }

    
    bool AsyncApp::WaitFor(WorkerId_t worker, Aurora::Threading::IWaitable *primitive, int timeoutMs)
    {
        auto curThread = GetThreadState();

        if (worker == curThread->id)
        {
            // TODO: timeout isn't respected here as well
            while (!Threading::WaitFor(primitive, 2))
            {
                while (this->Poll(false));
            }

            return true;
        }
        else
        {
            return Threading::WaitFor(primitive, timeoutMs);
        }
    }

    void AsyncApp::Start()
    {
        SysAssert(Spawn({0, 0}));
    }

    void AsyncApp::Main()
    {
        Entrypoint({0, 0});
    }

    void AsyncApp::Shutdown()
    {
        // Set shutdown trigger
        shuttingdown_ = true;

        // Unpause all
        for (auto &re : this->threads_)
        {
            for (auto &[id, worker] : re.second->workers)
            {
                auto &event = worker->running;
                if (event)
                {
                    event->Set();
                }
            }
        }
        
        // Drop all tasks from this point onwards 
        for (auto &re : this->threads_)
        {
            for (auto &[id, worker] : re.second->workers)
            {
                SysAssert(Barrier(worker->id, 0, true, true));
            }
        }
 
        // TODO: abort all pending tests

        // Signal the event loop to abort
        ShutdownOutOfTasks();
    }
    
    void AsyncApp::ShutdownOutOfTasks()
    {
        for (auto& [id, group]: this->threads_)
        {
            for (auto & [id, worker] : group->workers)
            {
                worker->threadObject->SendExitSignal();
            }

            if (group->cvVariable)
            {
                Threading::LockGuardPtr lol(group->cvWorkMutex);
                group->cvVariable->Broadcast();
            }
        }
    }

    bool AsyncApp::Exiting()
    {
        return shuttingdown_ || GetThreadState()->exiting;
    }

    bool AsyncApp::Spawn(WorkerId_t workerId)
    {
        Threading::LockGuardPtr lock(rwlock_->AsWritable());
        
        AuSPtr<GroupState> group;

        // Try fetch or allocate group
        {
            AuSPtr<GroupState>* groupPtr;
            if (!TryFind(this->threads_, workerId.first, groupPtr))
            {
                group = std::make_shared<GroupState>();
                
                if (!group->Init())
                {
                    SysPushErrorMem("Not enough memory to intiialize a new group state");
                    return false;
                }

                if (!TryInsert(this->threads_, std::make_pair(workerId.first, group)))
                {
                    return false;
                }
            }
            else
            {
                group = *groupPtr;
            }
        }

        // Assert worker does not already exist
        {
            AuSPtr<ThreadState>* ret;

            if (TryFind(group->workers, workerId.second, ret))
            {
                SysPushErrorGen("Thread ID already exists");
                return false;
            }
        }

        auto threadState = std::make_shared<ThreadState>();
        threadState->parent = group;
        threadState->running = Threading::Primitives::EventUnique(true, false, false);
        threadState->syncSema = Threading::Primitives::SemaphoreUnique(0);
        threadState->id = workerId;

        if (!threadState->IsSysThread())
        {
            Threading::Threads::AbstractThreadVectors handler;
            handler.DoRun = [=](const Threading::Threads::IAuroraThread *thread)
            {
                Entrypoint(threadState->id);
            };
            threadState->threadObject = Threading::Threads::ThreadUnique(handler);
            threadState->threadObject->Run();
        }
        else
        {
            threadState->threadObject = std::shared_ptr<Threading::Threads::IAuroraThread>(Threading::Threads::GetThread(), [](Threading::Threads::IAuroraThread *){});
        }
        
        group->workers.insert(std::make_pair(workerId.second, threadState));
        return true;
    }

    Threading::Threads::ThreadShared_t AsyncApp::ResolveHandle(WorkerId_t id)
    {
        auto group = GetGroup(id.first);
        if (!group)
        {
            return {};
        }
        
        AuSPtr<ThreadState>* ret;
        if (!TryFind(group->workers, id.second, ret))
        {
            return {};
        }

        return ret->get()->threadObject;
    }

    AuBST<ThreadGroup_t, AuList<ThreadId_t>> AsyncApp::GetThreads()
    {
        Threading::LockGuardPtr lock(rwlock_->AsReadable());

        AuBST<ThreadGroup_t, AuList<ThreadId_t>> ret;

        for (const auto &group : this->threads_)
        {
            AuList<ThreadId_t> workers;
            
            for (const auto &thread : group.second->workers)
            {
                workers.push_back(thread.second->id.second);
            }

            ret[group.first] = workers;
        }

        return ret;
    }

    WorkerId_t AsyncApp::GetCurrentThread()
    {
        return tlsWorkerId;
    }

    bool AsyncApp::Sync(ThreadGroup_t groupId, bool requireSignal, AuUInt32 timeoutMs)
    {
        Threading::LockGuardPtr lock(rwlock_->AsReadable());

        auto group = GetGroup(groupId);

        for (auto &jobWorker : group->workers)
        {
            if (!Barrier(jobWorker.second->id, timeoutMs, requireSignal, false)) // BAD!, should subtract time elapsed, clamp to, i dunno, 5ms min?
            {
                return false;
            }
        }

        return true;
    }

    void AsyncApp::Signal(ThreadGroup_t groupId)
    {
        Threading::LockGuardPtr lock(rwlock_->AsReadable());

        auto group = GetGroup(groupId);

        for (auto &jobWorker : group->workers)
        {
            jobWorker.second->running->Set();
        }
    }

    bool AsyncApp::SyncTimeout(ThreadGroup_t group, AuUInt32 ms)
    {
        return Sync(group, false, ms);
    }

    void AsyncApp::SyncAllSafe()
    {
        Threading::LockGuardPtr lock(rwlock_->AsReadable());

        for (const auto &re : this->threads_)
        {
            for (auto &jobWorker : re.second->workers)
            {
                SysAssert(Barrier(jobWorker.second->id, 0, false, false));
            }
        }
    }

    AuSPtr<GroupState>  AsyncApp::GetGroup(ThreadGroup_t type)
    {
        Threading::LockGuardPtr lock(rwlock_->AsReadable());

        AuSPtr<GroupState>* ret;
        if (!TryFind(this->threads_, type, ret))
        {
            return {};
        }

        return *ret;
    }
        
    AuSPtr<ThreadState> AsyncApp::GetThreadState()
    {
        auto id = GetCurrentThread();
        auto state = GetGroup(id.first);
        return state->workers[id.second];
    }

    void AsyncApp::Entrypoint(WorkerId_t id)
    {
        tlsWorkerId = id;

        auto auThread = Threading::Threads::GetThread();
        auto job      = GetThreadState();

        while (!auThread->Exiting())
        {
            // Do work (blocking)
            Poll(true);
        
            // Synchronization after pause
            job->running->Lock();
        }

        for (const auto &thread : job->features)
        {
            thread->Cleanup();
        }

        job->features.clear();
    }
   
    void AsyncApp::AddFeature(WorkerId_t id, AuSPtr<Threading::Threads::IThreadFeature> feature, bool async)
    {
        auto work = std::make_shared<BasicWorkStdFunc>(([=]()
        {
            GetThreadState()->features.push_back(feature);
            feature->Init();
        }));
        
        auto workItem = NewWorkItem(id, work, !async);
        workItem->Dispatch();

        if (!async)
        {
            workItem->BlockUntilComplete();
        }
    }

    void AsyncApp::AssertInThreadGroup(ThreadGroup_t group)
    {
        SysAssert(static_cast<WorkerId_t>(tlsWorkerId).first == group);
    }

    void AsyncApp::AssertWorker(WorkerId_t id)
    {
        SysAssert(static_cast<WorkerId_t>(tlsWorkerId) == id);
    }

    AUKN_SYM IAsyncApp *GetAsyncApp()
    {
        return &gAsyncApp;
    }
}