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

    File: IOSubmit.Linux.cpp
    Date: 2022-4-12
    Author: Reece
    Note: I want APCs, overlapped, and event based IO on Linux. Gib.
***/
#include <Source/RuntimeInternal.hpp>
#include "UnixIO.hpp"
#include <linux/aio_abi.h>
#include <sys/syscall.h>
#include <sys/epoll.h>
#include <poll.h>
#include <arpa/inet.h>
#include "IOSubmit.Linux.hpp"
#include <Source/Time/Time.hpp>
#include <Source/IO/Loop/Loop.hpp>
#include <Source/IO/Loop/LSEvent.hpp>

static int io_setup(unsigned nr, aio_context_t *ctxp)
{
    return syscall(__NR_io_setup, nr, ctxp);
}

static int io_destroy(aio_context_t ctx)
{
    return syscall(__NR_io_destroy, ctx);
}

static int io_submit(aio_context_t ctx, long nr, struct iocb **iocbpp)
{
    return syscall(__NR_io_submit, ctx, nr, iocbpp);
}

#if 0
static int io_getevents(aio_context_t ctx, long min_nr, long max_nr,
                        struct io_event *events,
                        struct timespec *timeout)
{
    return syscall(__NR_io_getevents, ctx, min_nr, max_nr, events, timeout);
}
#endif

#define read_barrier() __asm__ __volatile__("lfence" ::: "memory")

#define AIO_RING_MAGIC 0xa10a10a1

struct aio_ring {
    unsigned id; /** kernel internal index number */
    unsigned nr; /** number of io_events */
    unsigned head;
    unsigned tail;

    unsigned magic;
    unsigned compat_features;
    unsigned incompat_features;
    unsigned header_length; /** size of aio_ring */

    struct io_event events[0];
};

/* Code based on axboe/fio:
 * https://github.com/axboe/fio/blob/702906e9e3e03e9836421d5e5b5eaae3cd99d398/engines/libaio.c#L149-L172
*/
static int io_getevents(aio_context_t ctx, long min_nr, long max_nr,
                        struct io_event *events,
                        struct timespec *timeout)
{
    int i = 0;

    struct aio_ring *ring = (struct aio_ring *)ctx;
    if (ring == NULL || ring->magic != AIO_RING_MAGIC) {
        goto do_syscall;
    }

    while (i < max_nr) {
        unsigned head = ring->head;
        if (head == ring->tail) {
            /* There are no more completions */
            break;
        } else {
            /* There is another completion to reap */
            events[i] = ring->events[head];
            read_barrier();
            ring->head = (head + 1) % ring->nr;
            i++;
        }
    }

    if (i == 0 && timeout != NULL && timeout->tv_sec == 0 &&
        timeout->tv_nsec == 0) {
        /* Requested non blocking operation. */
        return 0;
    }

    if (i && i >= min_nr) {
        return i;
    }

do_syscall:
    return syscall(__NR_io_getevents, ctx, min_nr - i, max_nr - i,
               &events[i], timeout) + i;
}

static int io_cancel(aio_context_t ctx_id, struct iocb *iocb,
                     struct io_event *result)
{
    return syscall(SYS_io_cancel, ctx_id, iocb, result);
}

namespace Aurora::IO::UNIX
{
    static bool LinuxOverlappedSubmit(int fd, int op, AuUInt offset, ASubmittable *context, AuLoop::ILSEvent *optEvent);

    //////////////////////////////////////////////////////////////////
    // ASubmittable
    //////////////////////////////////////////////////////////////////

    ASubmittable::ASubmittable()
    {
    }

    ASubmittable::~ASubmittable()
    {
        if ((this->tempEPoll != 0) &&
            (this->tempEPoll != -1))
        {
            ::close(AuExchange(this->tempEPoll, -1));
        }
    }

    void ASubmittable::LIOS_SendProcess(AuUInt32 read, bool failure, int err, bool mark)
    {
        // Allow for reuse by releasing before dispatch
        // ...holding "this" ownership with a copy of the ref counter on the stack
        AuSPtr<void> pinSelf, pinMem;

        pinSelf = this->pin_;
        pinMem  = this->memPin_;

        LIOS_Reset();

        if (AuExchange(this->bIsReadPending, false))
        {
            // Psyche - it was just the poll half of a blocking read
            // We haven't read anything yet.
            if (!LinuxOverlappedSubmit(this->fd2, IOCB_CMD_PREAD, this->offset2 /* always zero */, this, this->optEvent2))
            {
                try
                {
                    LIOS_Process(0, true, 69, false);
                }
                catch (...)
                {
                    SysPushErrorCatch("IO Callback threw an exception");
                }
            }

            return;
        }

        try
        {
            LIOS_Process(read, failure, err, mark);
        }
        catch (...)
        {
            SysPushErrorCatch("IO Callback threw an exception");
        }
    }

    bool LIOS_PopOne()
    {
        return false;
    }

    void ASubmittable::LIOS_Init(const AuSPtr<void> &pin)
    {
        this->pin_ = pin;
    }

    void ASubmittable::LIOS_Reset()
    {
        this->pin_.reset();
        this->memPin_.reset();
    }

    void ASubmittable::SetMemory(const AuSPtr<AuMemoryViewRead> &view)
    {
        this->dataPtr_ = AuReinterpretCast<AuUInt64>(view->ptr);
        this->dataLen_ = view->length;
        this->memPin_  = view;
    }

    void ASubmittable::SetMemory(const AuSPtr<AuMemoryViewWrite> &view)
    {
        this->dataPtr_ = AuReinterpretCast<AuUInt64>(view->ptr);
        this->dataLen_ = view->length;
        this->memPin_  = view;
    }

    bool ASubmittable::HasState()
    {
        return bool(this->pin_);
    }
    
    AuUInt64 ASubmittable::GetBuf()
    {
        return this->dataPtr_;
    }

    AuUInt ASubmittable::GetBufLength()
    {
        return this->dataLen_; 
    }

    AuUInt64 ASubmittable::GetData()
    {
        return AuReinterpretCast<AuUInt64>(this);
    }

    iocb & ASubmittable::GetIOCB()
    {
        return this->cb;
    }

    int ASubmittable::GetOrCreateFdPollForBlockingRead(int fd)
    {
    #if 1
        return fd; // wtf freetards are incapable of writing an os. 
                   // the indirection of fds read state wasn't the problem.
                   // linux will never be a real kernel
                   // gnu will never be a real operating system
    #else
        // TODO (Reece): urgent: is this hack overkill? can we
        // just return fd?
        
        if ((this->tempEPoll == 0) ||
            (this->tempEPoll == -1))
        {
            epoll_event event;

            if ((this->tempEPoll = ::epoll_create1(0)) == -1)
            {
                SysPushErrorIO();
                return -1;
            }

            event.events   = EPOLLIN;
            event.data.ptr = nullptr;
            if (::epoll_ctl(this->tempEPoll, EPOLL_CTL_ADD, fd, &event) != 0)
            {
                SysPushErrorIO();
                ::close(this->tempEPoll);
                this->tempEPoll = -1;
                return -1;
            }
        }

        return this->tempEPoll;
    #endif
    }

    //////////////////////////////////////////////////////////////////
    // TLS
    //////////////////////////////////////////////////////////////////

    struct TLSIO
    {
        bool bInitialized {};
        aio_context_t context {};
        AuList<iocb*> submitPendingArray;
        AuUInt32 dwIoSubmits;

        ~TLSIO()
        {
            Deinit();
        }

        bool Init();
        void Deinit();
    };

    static thread_local TLSIO tlsLocal;

    static TLSIO *GetTls()
    {
        auto handle = &tlsLocal;

        if (!handle->bInitialized)
        {
            handle->bInitialized = handle->Init();
        }

        return handle->bInitialized ? handle : nullptr;
    }

    //////////////////////////////////////////////////////////////////
    // TLS IO IMPL
    //////////////////////////////////////////////////////////////////

    bool TLSIO::Init()
    {
        if (io_setup(1024, &this->context) != 0)
        {
            return false;
        }

        return true;
    }

    void TLSIO::Deinit()
    {
        io_destroy(this->context);
    }


    //////////////////////////////////////////////////////////////////
    // GLUE
    //////////////////////////////////////////////////////////////////

    static bool LinuxOverlappedTrySubmitWorkInternal(TLSIO *io)
    {
        int index {};
        int startingLength = io->submitPendingArray.size();

        while (index != startingLength)
        {
            int ret = io_submit(io->context, io->submitPendingArray.size() - index, io->submitPendingArray.data() + index);

            if (ret <= 0)
            {
                switch (ret)
                {
                case (-EAGAIN):
                {
                    SysPushErrorIO("Insufficient resources are available to queue any iocbs");
                    goto err;
                }

                case (-ENOSYS):
                {
                    SysPushErrorIO("io_submit() is not implemented on this architecture");
                    goto err;
                }

                case (-EINVAL):
                {
                    SysPushErrorIO("io submit context is dead");
                    goto err;
                }

                case (-EPERM):
                {
                    SysPanic("IOPRIO_CLASS_RT was requested but not granted to non-CAP_SYS_ADMIN (root?) process");
                }

                case (-EFAULT):
                {
                    SysPanic("One of the data structures points to invalid data.");
                }

                case (-EBADF):
                {
                    auto submittable = AuReinterpretCast<ASubmittable*>(io->submitPendingArray[index]->aio_data);
                    if (submittable)
                    {
                        submittable->LIOS_SendProcess(0, true, EBADF);
                    }
                }
                default:
                    SysPanic("unhandled case");
                }

            }
            else
            {
                io->dwIoSubmits += ret;
            }

            index += ret;
        }

        if (io->submitPendingArray.size() == index)
        {
            AuTryClear(io->submitPendingArray);
        }
        else
        {
            io->submitPendingArray.erase(io->submitPendingArray.begin(), io->submitPendingArray.begin() + index);
        }

        return true;

    err:

        if (index)
        {
            io->submitPendingArray.erase(io->submitPendingArray.begin(), io->submitPendingArray.begin() + index);
            return true;
        }
        else
        {
            return false;
        }
    } 

    static bool LinuxOverlappedTrySubmitWork()
    {
        auto io = GetTls();
        if (!io)
        {
            return false;
        }

        return LinuxOverlappedTrySubmitWorkInternal(io);
    }
  

    //////////////////////////////////////////////////////////////////
    // OVERLAPPED API
    //////////////////////////////////////////////////////////////////


    static bool LinuxOverlappedSubmit(int fd, int op, AuUInt offset, ASubmittable *context, AuLoop::ILSEvent *optEvent)
    {
        auto io = GetTls();
        if (!io)
        {
            return false;
        }
     
        iocb &submit = context->GetIOCB();
        submit.aio_data = context->GetData();
        submit.aio_lio_opcode = op;
        submit.aio_reqprio = 0;
        submit.aio_fildes = fd;
        submit.aio_offset = offset;
        submit.aio_buf = context->GetBuf();
        submit.aio_nbytes = context->GetBufLength();

        if (optEvent)
        {
            submit.aio_resfd = AuStaticCast<AuLoop::LSEvent>(optEvent)->GetHandle();
            submit.aio_flags |= IOCB_FLAG_RESFD;
        }

        return AuTryInsert(io->submitPendingArray, &submit);
    }

    static bool LinuxOverlappedReadWait(int fd, AuUInt offset, ASubmittable *context, AuLoop::ILSEvent *optEvent)
    {
        auto io = GetTls();
        if (!io)
        {
            return false;
        }
     
        SysAssert(offset == 0, "Read-blocking IO streams only");

        context->bIsReadPending = true;

        context->offset2 = offset; // redundant - always zero
        context->fd2 = fd;
        context->optEvent2 = optEvent;

        auto &submit = context->GetIOCB();
        submit.aio_data = context->GetData();
        submit.aio_lio_opcode = IOCB_CMD_POLL;
        submit.aio_reqprio = 0;
        submit.aio_fildes = context->GetOrCreateFdPollForBlockingRead(fd);
        submit.aio_offset = 0;
        submit.aio_buf = POLLIN;
        submit.aio_nbytes = 0;

        if (submit.aio_fildes == -1)
        {
            SysPushErrorIO();
            return false;
        }

        return AuTryInsert(io->submitPendingArray, &submit);
    }

    bool LinuxOverlappedSubmitRead(int fd, AuUInt offset, ASubmittable *context, AuLoop::ILSEvent *optEvent, bool bWaitForRead)
    {
        if (bWaitForRead)
        {
            return LinuxOverlappedReadWait(fd, offset, context, optEvent);
        }

        return LinuxOverlappedSubmit(fd, IOCB_CMD_PREAD, offset, context, optEvent);
    }

    bool LinuxOverlappedSubmitWrite(int fd, AuUInt offset, ASubmittable *context, AuLoop::ILSEvent *optEvent)
    {
        return LinuxOverlappedSubmit(fd, IOCB_CMD_PWRITE, offset, context, optEvent);
    }

    bool LinuxOverlappedPoll(AuUInt32 timeout)
    {
        timespec targetTime;
        io_event ioEvents[512];
        int temp;
        int dwApcsSent {};


        auto io = GetTls();
        if (!io)
        {
            return false;
        }

        AuInt64 iStartTime {};
        AuInt64 iTargetTime {};
        if (timeout)
        {
            iStartTime = AuTime::CurrentClockSteadyMS();
            iTargetTime = iStartTime + timeout;
        }

        if (!LinuxOverlappedTrySubmitWork())
        {
            SysPushErrorIO();
            errno = EBADF;
            return -1;
        }

        do
        {
            if (timeout)
            {
                auto delta = iTargetTime - AuTime::CurrentClockSteadyMS();
                if (delta <= 0)
                {
                    return dwApcsSent;
                }

                AuTime::ns2ts(&targetTime, delta);
            }

            temp = io_getevents(io->context, 1, 512, ioEvents, timeout ? &targetTime : nullptr);

            if (temp >= 0)
            {
                for (AU_ITERATE_N(i, temp))
                {
                    auto handle = AuReinterpretCast<ASubmittable *>(ioEvents[i].data);
                    io->dwIoSubmits--;

                    auto errNo = 0;
                    bool bError {};
                    AuUInt bytesTransacted {};

                    if (ioEvents[i].res < 0)
                    {
                        errNo  = 0 - ioEvents[i].res;
                        bError = true;
                    }
                    else
                    {
                        bytesTransacted = ioEvents[i].res;
                    }

                    handle->LIOS_SendProcess(bytesTransacted, bError, errNo);
                    dwApcsSent++;
                }
            }
            else
            {
                auto err = 0 - temp;
                if (err == EINTR)
                {
                    errno = EINTR;
                    break;
                }

                if (err == EINVAL)
                {
                    SysPushErrorArg();
                    break;
                }

                if (err == EFAULT)
                {
                    SysPanic("Either events or timeout is an invalid pointer.");
                }

                if (err == ENOSYS)
                {
                    SysPanic("io_getevents() is not implemented on this architecture.");                    
                }
            }

        } while (timeout);

        return dwApcsSent;
    }


    bool SendIOBuffers()
    {
        return LinuxOverlappedTrySubmitWork();
    }

    int LinuxOverlappedEpollShim(int epfd, struct epoll_event *events,
                                 int maxevents, int timeout)
    {
        timespec targetTime;
        auto io = GetTls();
        if (!io)
        {
            return epoll_wait(epfd, events, maxevents, timeout);
        }

        AuInt64 iStartTime {};
        AuInt64 iTargetTime {};
        if (timeout)
        {
            iStartTime = AuTime::CurrentClockSteadyMS();
            iTargetTime = iStartTime + timeout;
        }

        if (!LinuxOverlappedTrySubmitWork())
        {
            SysPushErrorIO();
            errno = EBADF;
            return -1;
        }

        if (!io->dwIoSubmits)
        {
            return epoll_wait(epfd, events, maxevents, timeout);
        }

        // evil nested epoll garbage
        // but i'm sure the kevent way would be more inefficient
        iocb pollSubmit {};
        pollSubmit.aio_fildes = epfd;
        pollSubmit.aio_lio_opcode = IOCB_CMD_POLL;
        pollSubmit.aio_buf = POLLIN;

        iocb * ptr = &pollSubmit;
        iocb ** ptrArray = &ptr;

        if (io_submit(io->context, 1, ptrArray) <= 0)
        {
            errno = EFAULT;
            SysPushErrorIO();
            return -1;
        }

        bool bEpollTriggered {};
        io_event ioEvents[512];
        int temp;

        do
        {
            if (timeout)
            {
                auto delta = iTargetTime - AuTime::CurrentClockSteadyMS();
                if (delta <= 0)
                {
                    return dwApcsSent;
                }

                AuTime::ns2ts(&targetTime, delta);
            }

            temp = io_getevents(io->context, 1, 512, ioEvents, timeout ? &targetTime : nullptr);

            if (temp >= 0)
            {
                for (AU_ITERATE_N(i, temp))
                {
                    auto handle = AuReinterpretCast<ASubmittable *>(ioEvents[i].data);
                    if (!handle)
                    {
                        // loop source has message
                        bEpollTriggered = true;
                    }
                    else
                    {
                        io->dwIoSubmits--;

                        auto errNo = 0;
                        bool bError {};
                        AuUInt bytesTransacted {};

                        if (ioEvents[i].res < 0)
                        {
                            errNo  = 0 - ioEvents[i].res;
                            bError = true;
                        }
                        else
                        {
                            bytesTransacted = ioEvents[i].res;
                        }

                        handle->LIOS_SendProcess(bytesTransacted, bError, errNo);
                    }
                }
            }
            else
            {
                auto err = 0 - temp;
                if (err == EINTR)
                {
                    errno = EINTR;
                    break;
                }

                if (err == EINVAL)
                {
                    SysPushErrorArg();
                    break;
                }

                if (err == EFAULT)
                {
                    SysPanic("Either events or timeout is an invalid pointer.");
                }

                if (err == ENOSYS)
                {
                    SysPanic("io_getevents() is not implemented on this architecture.");                    
                }
            }

        } while (timeout ? !bEpollTriggered : false);

        io_event finalEpollEvent {};
        if ((bEpollTriggered) ||
            (io_cancel(io->context, ptr, &finalEpollEvent) == 0))
        {
            // TODO (Reece): if finalEpollEvent.res == 1, bEpollTriggered = true?
        }
        else
        {
            // Do I care?
            SysPushErrorIO();
            // I don't
            // I do again
        }

        if (bEpollTriggered)
        {
            return epoll_wait(epfd, events, maxevents, 0);
        }
        else
        {
            return 0;
        }
    }

    bool LinuxOverlappedWaitForOne(AuUInt32 timeout, AuUInt read, AuUInt write, bool &bReadTriggered, bool &bWriteTriggered)
    {
        timespec targetTime;
        auto io = GetTls();

        bWriteTriggered = false;
        bReadTriggered = false;

        if (!io)
        {
            return false;
        }

        AuInt64 iStartTime {};
        AuInt64 iTargetTime {};
        if (timeout)
        {
            iStartTime = AuTime::CurrentClockSteadyMS();
            iTargetTime = iStartTime + timeout;
        }

        if (!LinuxOverlappedTrySubmitWork())
        {
            SysPushErrorIO();
            errno = EBADF;
            return false;
        }

        if (!io->dwIoSubmits)
        {
            return false;
        }

        iocb submit {};
        iocb readSubmit {};
        iocb writeSubmit {};
        submit.aio_lio_opcode = IOCB_CMD_POLL;

        iocb * ptrArray[2];
        int iocbIdx {};

        if (read != -1)
        {
            readSubmit = submit;
            readSubmit.aio_fildes = read;
            readSubmit.aio_data = 1;
            readSubmit.aio_buf = POLLIN;
            ptrArray[iocbIdx++] = &readSubmit;
        }

        if (write != -1)
        {
            writeSubmit = submit;
            writeSubmit.aio_fildes = write;
            writeSubmit.aio_data = 2;
            writeSubmit.aio_buf = POLLOUT;
            ptrArray[iocbIdx++] = &writeSubmit;
        }

        if (io_submit(io->context, iocbIdx, ptrArray) <= 0)
        {
            errno = EFAULT;
            SysPushErrorIO();
            return -1;
        }

        io_event ioEvents[512];
        int temp;

        do
        {
            if (timeout)
            {
                auto delta = iTargetTime - AuTime::CurrentClockSteadyMS();
                if (delta <= 0)
                {
                    return dwApcsSent;
                }

                AuTime::ns2ts(&targetTime, delta);
            }

            temp = io_getevents(io->context, 1, 512, ioEvents, timeout ? &targetTime : nullptr);

            if (temp >= 0)
            {
                for (AU_ITERATE_N(i, temp))
                {
                    if (ioEvents[i].data == 1)
                    {
                        bReadTriggered = true;
                    }
                    else if (ioEvents[i].data == 2)
                    {
                        bWriteTriggered = true;
                    }
                    else
                    {
                        auto handle = AuReinterpretCast<ASubmittable *>(ioEvents[i].data);

                        io->dwIoSubmits--;

                        auto errNo = 0;
                        bool bError {};
                        AuUInt bytesTransacted {};

                        if (ioEvents[i].res < 0)
                        {
                            errNo  = 0 - ioEvents[i].res;
                            bError = true;
                        }
                        else
                        {
                            bytesTransacted = ioEvents[i].res;
                        }

                        handle->LIOS_SendProcess(bytesTransacted, bError, errNo);
                    }
                }
            }
            else
            {
                auto err = 0 - temp;
                if (err == EINTR)
                {
                    errno = EINTR;
                    break;
                }

                if (err == EINVAL)
                {
                    SysPushErrorArg();
                    break;
                }

                if (err == EFAULT)
                {
                    SysPanic("Either events or timeout is an invalid pointer.");
                }

                if (err == ENOSYS)
                {
                    SysPanic("io_getevents() is not implemented on this architecture.");                    
                }
            }

        } while (timeout ? (!bReadTriggered && !bWriteTriggered) : false);

        for (int i = 0; i < iocbIdx; i++)
        {
            io_event finalEpollEvent {};

            if (i == 0)
            {
                if ((bReadTriggered) ||
                    ((read == -1) && (bWriteTriggered)))
                {
                    continue;
                }
            }
            else if ((i == 1) && (bWriteTriggered))
            {
                continue;
            }
            
            if (io_cancel(io->context, ptrArray[i], &finalEpollEvent) == 0)
            {
                // TODO (Reece): if finalEpollEvent.res == 1, bEpollTriggered = true?
            }
            else
            {
                // Do I care?
                SysPushErrorIO();
                // I don't
                // I do again
            }
        }

        return true;
    }

    bool LinuxOverlappedWaitForAtleastOne(AuUInt32 timeout, const AuList<AuUInt> &handles, const AuList<AuUInt> &handlesWrite, AuUInt &one, AuUInt &two)
    {
        // TODO:
        return false;
    }

    bool LinuxOverlappedYield()
    {
        io_event ioEvents[512];
        int temp;
        timespec targetTime {};
        auto io = GetTls();

        if (!io)
        {
            return false;
        }

        if (!LinuxOverlappedTrySubmitWork())
        {
            SysPushErrorIO();
            errno = EBADF;
            return false;
        }

        if (!io->dwIoSubmits)
        {
            return false;
        }

        temp = io_getevents(io->context, 1, 512, ioEvents, &targetTime);

        if (temp >= 0)
        {
            for (AU_ITERATE_N(i, temp))
            {
                auto handle = AuReinterpretCast<ASubmittable *>(ioEvents[i].data);

                io->dwIoSubmits--;

                auto errNo = 0;
                bool bError {};
                AuUInt bytesTransacted {};

                if (ioEvents[i].res < 0)
                {
                    errNo  = 0 - ioEvents[i].res;
                    bError = true;
                }
                else
                {
                    bytesTransacted = ioEvents[i].res;
                }

                handle->LIOS_SendProcess(bytesTransacted, bError, errNo);
            }
        }
        else
        {
            auto err = 0 - temp;
            if (err == EINTR)
            {
                errno = EINTR;
                // Assume signal is also a valid yield
            }

            if (err == EINVAL)
            {
                SysPushErrorArg();
                return false;
            }

            if (err == EFAULT)
            {
                SysPanic("Either events or timeout is an invalid pointer.");
            }

            if (err == ENOSYS)
            {
                SysPanic("io_getevents() is not implemented on this architecture.");                    
            }
        }

        return true;
    }
}