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

    File: Async.hpp
    Date: 2021-6-10
    Author: Reece
***/
#pragma once

namespace Aurora::Async
{
    class IWorkItem;
    class IAsyncApp;

    using AVoid = AuUInt8;
    
    AUKN_SYM IAsyncApp *GetAsyncApp();

    using ThreadGroup_t = AuUInt8;
    using ThreadId_t    = AuUInt16;
    
    using WorkerId_t = std::pair<ThreadGroup_t, ThreadId_t>;
    using DispatchTarget_t = std::pair<ThreadGroup_t, std::optional<ThreadId_t>>;

    struct IWorkItemHandler
    {
        enum class EProcessNext
        {	
            eInvalid = -1,
            eFinished = 0,
            eRerun,
            eSchedule,
            eFailed
        };

        struct ProcessInfo 
        {
            ProcessInfo(bool finished) : type(finished ? EProcessNext::eFinished : EProcessNext::eFailed) {}
            ProcessInfo(EProcessNext type) : type(type) {}
            ProcessInfo(const AuList<AuSPtr<IWorkItem>> &blockedBy) : type(EProcessNext::eSchedule), waitFor(blockedBy) {}
            // ...

            EProcessNext type;
            AuList<AuSPtr<IWorkItem>> waitFor;
            AuUInt32 reschedMs;
            //AuUInt64 reschedNs;		
        };

        virtual void DispatchFrame(ProcessInfo &info) = 0;
        virtual void Shutdown() = 0;
    };
    
    
    template<typename Info_t = AVoid, typename Result_t = AVoid>
    struct FJob
    {
        std::function<void(const Info_t &, const Result_t &)> onSuccess = 0;
        std::function<void(const Info_t &, bool)>             onFailure = 0;
    };

    template<typename Info_t = AVoid, typename Result_t = AVoid>
    struct CJob
    {
        void(* onSuccess)(const Info_t &, const Result_t &);         // 
        void(* onFailure)(const Info_t &, bool taskNeverDispatched); // called from caller thread if taskNeverDispatched
    };
    
    template<typename Info_t = AVoid, typename Result_t = AVoid>
    struct FTask
    {
        std::function<std::optional<Result_t>(const Info_t &)> onFrame = 0;
    };

    template<typename Info_t = AVoid, typename Result_t = AVoid>
    struct CTask
    {
        std::optional<Result_t>(* onFrame)(const Info_t &);
    };
    

    class IWorkItem 
    {
    public:
        virtual void WaitFor(const AuSPtr<IWorkItem> &workItem)    = 0;
        virtual void WaitFor(const AuList<AuSPtr<IWorkItem>> &workItem) = 0;
        virtual void SetSchedTime(AuUInt32 ms)                     = 0;

        virtual void Dispatch()                                    = 0;

        virtual bool BlockUntilComplete()                          = 0;
        virtual bool HasFinished()                                 = 0;
        virtual bool HasFailed()                                   = 0;
    };
 
    
    AUKN_SYM AuSPtr<IWorkItem> NewWorkItem(const DispatchTarget_t &worker, const AuSPtr<IWorkItemHandler> &task, bool supportsBlocking = false);

    struct BasicWorkStdFunc : IWorkItemHandler
    {
        std::function<void()> callback;
        std::function<void()> shutdown;
    
        BasicWorkStdFunc(std::function<void()> &&callback, std::function<void()> &&error) : callback(std::move(callback)),  shutdown(std::move(shutdown))
        {}

        BasicWorkStdFunc(std::function<void()> &&callback) : callback(std::move(callback))
        {}
        
        BasicWorkStdFunc(const std::function<void()> &callback) : callback(callback)
        {}
        
        BasicWorkStdFunc(const std::function<void()> &callback, const std::function<void()> &shutdown) : callback(callback), shutdown(shutdown)
        {}
        
    private:

        void DispatchFrame(ProcessInfo &info) override
        {
            try
            {
                callback();
            } 
            catch (...)
            {
                Debug::PrintError();
            }
        }
        
        void Shutdown() override
        {
            try
            {
                if (shutdown)
                {
                    shutdown();
                }
            } 
            catch (...)
            {
                Debug::PrintError();
            }
        }
    };

    template<typename Info_t, typename Result_t, typename Task_t = FTask<Info_t, Result_t>, typename Job_t = FJob<Info_t, Result_t>>
    struct BasicWorkCallback : IWorkItemHandler, std::enable_shared_from_this<IWorkItemHandler>
    {
        BasicWorkCallback()
        {
            caller = GetAsyncApp()->GetCurrentThread();
        }

        Task_t task;
        Job_t callback;

        Info_t input;
        
    private:
        
        static constexpr bool IsCallbackPtr = std::is_pointer_v<Job_t> || is_base_of_template<std::shared_ptr, Job_t>::value;
        static constexpr bool IsTaskPtr = std::is_pointer_v<Task_t>    || is_base_of_template<std::shared_ptr, Task_t>::value;

        WorkerId_t caller;

        void DispatchFrame(ProcessInfo &info) override
        {
            std::optional<Result_t> ret;

            if constexpr (IsTaskPtr)
            {
                ret = task->onFrame(input);
            }
            else
            {
                ret = task.onFrame(input);
            }

            auto pin = std::static_pointer_cast<std::remove_pointer_t<decltype(this)>>(this->shared_from_this());

            std::function<void()> func = [ret, pin]()
            {
                try
                {
                    if (ret.has_value())
                    {
                        if constexpr (IsCallbackPtr)
                        {
                            pin->callback->onSuccess(pin->input, *ret);
                        }
                        else
                        {
                            pin->callback.onSuccess(pin->input, *ret);
                        }
                    }
                    else
                    {
                        pin->CallOnFailure(false);
                    }
                } 
                catch (...)
                {
                    Debug::PrintError();
                }
            };

            try
            {
                if (caller == GetAsyncApp()->GetCurrentThread())
                {
                    func();
                }
                else
                {
                    std::function<void()> err = [pin]()
                    {
                        pin->CallOnFailure(false);
                    };

                    // TODO: this is somewhat evil. double alloc when we could reuse this
                    NewWorkItem(caller, std::make_shared<BasicWorkStdFunc>(func, err))->Dispatch();
                }
            } 
            catch (...)
            {
                Debug::PrintError();
                Shutdown();
            }
        }
        
        void Shutdown() override
        {
            try
            {
                CallOnFailure(true);
            } 
            catch (...)
            {
                Debug::PrintError();
            }
        }

        void CallOnFailure(bool fail)
        {
            if constexpr (IsCallbackPtr)
            {
                if constexpr (is_base_of_template<std::function, decltype(callback->onFailure)>::value)
                {
                    if (!callback->onFailure)
                    {
                        return;
                    }
                }
                
                callback->onFailure(input, fail);
            }
            else
            {
                if constexpr (is_base_of_template<std::function, decltype(callback.onFailure)>::value)
                {
                    if (!callback.onFailure)
                    {
                        return;
                    }
                }
                callback.onFailure(input, fail);
            }
        }
    };
    
    template<typename Frame_t = std::function<void()>, typename Cleanup_t = std::function<void()>>
    struct WorkItemCallabale : IWorkItemHandler
    {
        Frame_t frame;
        Cleanup_t cleanup;

    private:
        void DispatchFrame(ProcessInfo &info) override
        {
            frame();
            info.type = IWorkItemHandler::EProcessNext::eFinished;
        }

        void Shutdown() override
        {
            cleanup();
        }
    };

    template<typename B, typename... Args>
    static void TranslateAsyncFunctionToDispatcher()
    {

    }

    class IAsyncApp
    {
    public:
        // Main thread logic
        virtual void Start()                                                            = 0;
        virtual void Main()                                                             = 0;
        virtual void Shutdown()                                                         = 0;
        virtual bool Exiting()                                                          = 0;

        // Spawning
        virtual bool Spawn(WorkerId_t)                                                  = 0;
        virtual Threading::Threads::ThreadShared_t ResolveHandle(WorkerId_t)            = 0;
        virtual AuBST<ThreadGroup_t, AuList<ThreadId_t>> GetThreads()                   = 0;
        virtual WorkerId_t GetCurrentThread()                                           = 0;

        // Synchronization
        virtual bool Sync(ThreadGroup_t group, bool requireSignal = false, AuUInt32 timeout = 0) = 0;
        virtual void Signal(ThreadGroup_t group)                                        = 0;
        
        virtual bool WaitFor(WorkerId_t unlocker, Threading::IWaitable *primitive, int ms) = 0; // when unlocker = this, pump event loop

        virtual bool SyncTimeout(ThreadGroup_t group, AuUInt32 ms)                      = 0;

        virtual void SyncAllSafe()                                                      = 0;

        // Features
        virtual void AddFeature(WorkerId_t id, AuSPtr<Threading::Threads::IThreadFeature> feature, bool async = false) = 0;
        
        // Debug
        virtual void AssertInThreadGroup(ThreadGroup_t thread)                          = 0;
        virtual void AssertWorker(WorkerId_t id)                                        = 0;
    };

}