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

    File: AuIPCMutexFutex.Linux.cpp
    Date: 2022-
    Author: Reece
    Note: 
***/
#include <Source/RuntimeInternal.hpp>
#include "IPC.hpp"
#include "AuIPCHandle.hpp"
#include "AuIPCMutexFutex.Linux.hpp"
#include "AuIPCPrimitives.Linux.hpp"
#include "AuIPCMemory.Unix.hpp"

// LINUX SYSCALL APIS
#include <linux/futex.h> 
#include <syscall.h>

// INTERNAL UTILS
// ...IO / FD SHARING
#include <Source/IO/UNIX/FDIpcServer.hpp>
// ...TIME UTILS
#include <Source/Time/Time.hpp>

////////////////////////////////////////////////////////////////////////////////////
// CONSTANTS
////////////////////////////////////////////////////////////////////////////////////

static const AuUInt8  kMaxFutexes          = 128;
static const AuUInt32 kFutexArraySize      = AuUInt32(kMaxFutexes) * (sizeof(AuUInt64) * 3);

static const AuUInt32 kFutexIsValid        = 0x80000000;
static const AuUInt32 kFutexIsDead         = 0x40000000;
static const AuUInt32 kFutexIsHasOwner     = 0x20000000;

//static const AuUInt32 kFutexValueLocked    = kFutexIsHasOwner | kFutexIsValid | 1;
static const AuUInt32 kFutexValueUnlocked  = kFutexIsHasOwner;
static const AuUInt32 kFutexValueNULL      = 0;

static AuUInt32 gConstNull                 = 0;
 

////////////////////////////////////////////////////////////////////////////////////
// VARIABLES
////////////////////////////////////////////////////////////////////////////////////

struct FutexObject
{
    union
    {
        AuUInt64 maxWord;
        void *nextPtr;
    };

    union
    {
        AuUInt32 futex;
        AuUInt64 futexPadded;
    };
};

static_assert(sizeof(FutexObject) == 16);

static AuThreadPrimitives::SpinLock gLock;
static AuSPtr<AuIPC::IPCSharedMemory> gFutexSharedMemory;
static FutexObject *gFutexArray;
static bool gFutexInit {};

static AuIOIPC::IMutexClosedHook * gFutexCallbacks[kMaxFutexes];


////////////////////////////////////////////////////////////////////////////////////
// IMPLEMENTATION
////////////////////////////////////////////////////////////////////////////////////

static void InitFutexAPI()
{
    AU_LOCK_GUARD(gLock);

    if (AuExchange(gFutexInit, true))
    {
        return;
    }

    gFutexSharedMemory = AuIOIPC::NewSharedMemory(kFutexArraySize);
    SysAssert(gFutexSharedMemory);

    gFutexArray = gFutexSharedMemory->GetMemory().Begin<FutexObject>(); 
}

struct MagicFutexLinkHeader : robust_list_head
{
    AuUInt32 linkCount {};
};

struct FutexContext
{
    bool bInit {};
    AuThreadPrimitives::SpinLock lock;
    AuUInt32 tid {};

    bool Init();

    bool SetGrugSelf();

    bool Link(AuUInt32 *ptr);
    bool Unlink(AuUInt32 *ptr);

    MagicFutexLinkHeader futexArrayHeader {};
};


static FutexContext gFutexContext;
void LinuxSuperSecretFuckGlibc();
static void LinuxLockFutex(AuUInt32 *futex);

void LinuxSuperSecretFuckGlibc()
{
    // Fun: You have to define an entry-relative-offset within a linked list header, hard coding an ABI, for every user
    //      program in the tasks/processes address space. Low-iq linux kernel comments state "tehe" check with the glibc folk.
    //  
    //      Counter, they aren't "folk," they aren't even real people.
    //      Fuck you, and fuck your buzzword mutex that hasn't evolved into a stable API since its initial hack of an
    //      implementation 20 years ago. I don't want to make a fucking array of pthreads (40+ bytes for a single atomic).
    //      I don't want to fucking define a system-wide abi, matching ONE OF MANY fucking glibc ABIs, any given process
    //      could be arbitrarily linked against. 
    // 
    //      As a wise man once said, "Linus says fuck you Nvidia, I say f............! That's what I say."
    // ---------------------------------------------------------------------------------------------------------------------
    //      Unrelated, here's what FreeBSD says about the UMUTEX_ROBUST list set operation:
    //           Note that if any 32-bit ABI compatibility is being requested, then care
    //           must be taken with robust lists.  A single thread may not mix 32-bit com-
    //           patible robust lists with native robust lists.  The first
    //           UMTX_OP_ROBUST_LISTS call in a given thread determines which ABI that
    //           thread will use for robust lists going forward.
    // 
    //           Code: https://github.com/freebsd/freebsd-src/blob/27a9392d543933f1aaa4e4ddae2a1585a72db1b2/sys/kern/kern_umtx.c#L4150
    //
    //      ...FreeBSD just copied the fucking glibc tards between 2012-present didn't they? I bet they were "inspired" by glibcs
    //      nptl implementation on Linux, and thought hey, let's just copy this so we can have a functional CRT with shared pt-mutexes
    // ---------------------------------------------------------------------------------------------------------------------
    //      I'll just have to use a dedicated watcher process that'll teardown a robust list of only standard
    //       entries limited to the Aurora IPC origin. Will use the grug thread for this bc i dont foresee user
    //       code locking shared pthread-mutexs under the few user-interfaces grug may call out to.
    //
    SysAssert(gFutexContext.SetGrugSelf());
}

bool FutexContext::SetGrugSelf()
{
    // Specify the magic word to use...
    this->tid = gettid();

    // Update the header
    this->futexArrayHeader.list.next       = &this->futexArrayHeader.list;
    this->futexArrayHeader.futex_offset    = 8;
    this->futexArrayHeader.list_op_pending = NULL;

    // Update TLS
    if (Aurora::set_robust_list(AuReinterpretCast<robust_list_head *>(&this->futexArrayHeader.list), sizeof(robust_list_head)) != 0)
    {
        SysPushErrorIO("Set robust list failed");
        return false;
    }

    return true;
}

bool FutexContext::Init()
{
    AU_LOCK_GUARD(this->lock);

    if (AuExchange(this->bInit, true))
    {
        return true;
    }

    InitFutexAPI();

    return true;
}

bool FutexContext::Link(AuUInt32 *ptr)
{
    if (!ptr)
    {
        return false;
    }

    if (!Init())
    {
        return false;
    }

    AU_LOCK_GUARD(this->lock);
    auto temp = AuReinterpretCast<FutexObject *>(AuUInt(ptr) - offsetof(FutexObject, futex));

    auto firstElement = futexArrayHeader.list.next;
    temp->nextPtr = firstElement;

    futexArrayHeader.list_op_pending = nullptr;
    futexArrayHeader.list.next = (robust_list *)temp;
    futexArrayHeader.linkCount++;
    return true;
}

bool FutexContext::Unlink(AuUInt32 *ptr)
{
    if (!ptr)
    {
        return false;
    }

    if (!Init())
    {
        return false;
    }

    AU_LOCK_GUARD(this->lock);

    FutexObject *cur      { (FutexObject *)this->futexArrayHeader.list.next };
    FutexObject *prevLink { cur };

    for (int i = 0; i < this->futexArrayHeader.linkCount; i++)
    {
        if (&cur->futex != ptr)
        {
            prevLink = cur;
            cur      = (FutexObject *)cur->nextPtr;
            continue;
        }

        prevLink->nextPtr = cur->nextPtr;
        this->futexArrayHeader.linkCount--;
        return true;
    }

    return false;
}

static AuUInt8 AllocateFutex()
{
    gFutexContext.Init();
    if (!gFutexArray)
    {
        return 255;
    }

    for (AuUInt32 i = 0;
         i < kMaxFutexes;
         i++)
    {
        if (AuAtomicCompareExchange<AuUInt32>(&gFutexArray[i].futex, kFutexValueUnlocked, kFutexValueNULL) == kFutexValueNULL)
        {
            if (gFutexCallbacks[i])
            {
                continue;
            }

            return i;
        }
    }

    return 255;
}

static bool TryReleaseFutex(AuUInt8 index)
{
    auto old      = gFutexCallbacks[index];
    auto oldState = gFutexArray[index].futexPadded;

    if ((old) && 
        (!old->OnClosed()))
    {
        return false;
    }

    if (AuAtomicCompareExchange<AuUInt32>(&gFutexArray[index].futex, kFutexValueUnlocked, oldState) != oldState)
    {
        return false;
    }

    return true;
}

static void FreeFutex(AuUInt8 index)
{
    gFutexArray[index].futexPadded = 0;
    gFutexCallbacks[index] = nullptr;
}

static void LinuxAddRobustFutexSlow(AuUInt32 *futex)
{
    SysAssert(gFutexContext.Init());
    SysAssert(gFutexContext.Link(futex));
}

static void LinuxRemoveRobustFutexSlow(AuUInt32 *futex)
{
    SysAssert(gFutexContext.Init());
    if (!gFutexContext.Unlink(futex))
    {
        SysPushErrorIO("Unlink futex error: {}", fmt::ptr(futex));
    }
}

static bool LinuxLockFutex(AuUInt32 *futex, AuUInt32 timeout)
{
    bool bContended;
    struct timespec tspec;
    AuUInt32 value = gFutexContext.tid;

    if (timeout)
    {
        AuTime::ms2tsabs(&tspec, timeout);
    }

    do
    {
        auto old = AuAtomicCompareExchange<AuUInt32>(futex, value, kFutexValueUnlocked);
        bContended = old != kFutexValueUnlocked;
        if (bContended)
        {
            int res = Aurora::futex_wait_shared(futex, old, timeout ? &tspec : nullptr);
            if (res < 0)
            {
                if (res == ETIMEDOUT || errno == ETIMEDOUT)
                {
                    return false;
                }
                else if (res == -EAGAIN || errno == EAGAIN)
                {
                    bContended = true;
                }
                else
                {
                    SysPushErrorIO("FUTEX ERROR: {}", res);
                    return false;
                }
            }
            else
            {
                bContended = false;
            }
        }
    }
    while (bContended);

    ::LinuxAddRobustFutexSlow(futex);
    return true;
}

static bool LinuxTryLockFutex(AuUInt32 *futex)
{
    if (AuAtomicCompareExchange<AuUInt32>(futex,
                                          gFutexContext.tid,
                                          kFutexValueUnlocked) != kFutexValueUnlocked)
    {
        return false;
    }

    LinuxAddRobustFutexSlow(futex);
    return true;
}

static bool LinuxUnlockFutex(AuUInt32 *futex)
{
    LinuxRemoveRobustFutexSlow(futex);

    if (AuAtomicCompareExchange<AuUInt32>(futex,
                                          kFutexValueUnlocked,
                                          gFutexContext.tid) != gFutexContext.tid)
    {
        return false;
    }

    Aurora::futex_wake_shared(futex, 1);

    return true;
}

void LinuxSuperSecretIOTick()
{
    if (!gFutexInit)
    {
        return;
    }

    if (!gFutexArray)
    {
        return;
    }

    static Aurora::Utility::RateLimiter gLimiter;

    if (!gLimiter.nextTriggerTime)
    {
        gLimiter.noCatchUp = true;
        gLimiter.SetNextStep(AuMSToNS<AuUInt64>(3'000));
    }

    if (!gLimiter.CheckExchangePass())
    {
        return;
    }

    for (AuUInt32 i = 0;
         i < kMaxFutexes;
         i++)
    {
        auto val = gFutexArray[i].futex;
        val &= ~(0x3fffffff);
        if ((val & kFutexIsDead) != 0) 
        {
            ::TryReleaseFutex(i);
        }
    }
}

namespace Aurora::IO::IPC
{
    static AuThreadPrimitives::SpinLock gLock;
    static AuBST<AuPair<AuUInt64 /*cookie*/, AuUInt32 /*pid*/>, AuWPtr<IPCSharedMemory>> gSharedViewCache;

    //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    // Mutexes
    //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

    IPCMutexProxy::IPCMutexProxy(AuUInt32 index) :
        mutex_(),
        bOwned(true),
        index_(index)
    {
        if (this->mutex_.HasValidHandle())
        {
            if (IO::UNIX::FDServe(this->GetHandle(), this->token_))
            {
                //this->handle_.PushId(EIPCHandleType::eIPCPrimitiveMutex, token);
            }
            else
            {
                this->mutex_.~LSMutex();
            }
        }
        
        this->mem_ = gFutexSharedMemory;
        this->mutex_.bNoAutoRel = true;

        gFutexCallbacks[index] = this;
    }

    IPCMutexProxy::IPCMutexProxy(int handle, AuSPtr<IPCSharedMemory> mem, AuUInt32 index) :
        mutex_(handle),
        mem_(mem),
        index_(index)
    {
        if (this->mutex_.HasValidHandle())
        {
            if (IO::UNIX::FDServe(this->GetHandle(), this->token_))
            {
                //this->handle_.PushId(EIPCHandleType::eIPCPrimitiveMutex, token);
            }
            else
            {
                this->mutex_.~LSMutex();
            }
        }
        
        this->mutex_.bNoAutoRel = true;
    }

    IPCMutexProxy::~IPCMutexProxy()
    {
        IO::UNIX::FDServeEnd(this->token_);

        if (this->bOwned)
        {
            ::FreeFutex(this->index_);
        }
    }

    AuUInt32 *IPCMutexProxy::GetFutex()
    {
        return &this->mem_->GetMemory().Begin<FutexObject>()[this->index_].futex;
    }

    bool IPCMutexProxy::Unlock()
    {
        auto futex = this->GetFutex();
        if (!futex)
        {
            return false;
        }

        if (!::LinuxUnlockFutex(futex))
        {
            return false;
        }

        SysAssert(this->mutex_.Unlock());
        this->leakSelf_.reset();

        return true;
    }

    bool IPCMutexProxy::IsSignaled()
    {
        auto futex = this->GetFutex();
        if (!futex)
        {
            return false;
        }

        if (!::LinuxTryLockFutex(futex))
        {
            return false;
        }

        if (!this->mutex_.IsSignaled())
        {
            ::LinuxUnlockFutex(futex);
            return false;
        }

        this->leakSelf_ = AuSharedFromThis();

        return true;
    }

    bool IPCMutexProxy::WaitOn(AuUInt32 timeout)
    {
        auto futex = this->GetFutex();
        if (!futex)
        {
            return false;
        }

        if (!::LinuxLockFutex(futex, timeout))
        {
            return false;
        }

        if (!this->mutex_.IsSignaled())
        {
            ::LinuxUnlockFutex(futex);
            return false;
        }

        this->leakSelf_ = AuSharedFromThis();

        return true;
    }

    bool IPCMutexProxy::OnClosed()
    {
        auto futex = this->GetFutex();

        if (this->pMutexClosedHook)
        {
            if (!this->pMutexClosedHook->OnClosed())
            {
                return false;
            }
        }

        if (futex)
        {
            auto a = *futex;
            if (*futex == kFutexIsDead)
            {
                this->mutex_.Unlock();
            }
        }

        return true;
    }

    Loop::ELoopSource IPCMutexProxy::GetType()
    {
        return this->mutex_.GetType();
    }

    AuString IPCMutexProxy::ExportToString()
    {
        IPC::IPCHandle handle;

        handle.PushId(EIPCHandleType::eIPCPrimitiveMutex, this->token_);
        SysAssert(this->mem_);
        handle.PushId(EIPCHandleType::eIPCMemory, AuStaticCast<IPCSharedMemoryImpl>(this->mem_)->handle_.values[0].token);
        handle.values[0].token.word = this->index_;

        return handle.ToString();
    }

    AUKN_SYM AuSPtr<IPCMutex>     NewMutex()
    {
        auto futex = ::AllocateFutex();
        if (futex == 255)
        {
            return {};
        }

        auto object = AuMakeShared<IPCMutexProxy>(futex);
        if (!object)
        {
            SysPushErrorMem();
            return {};
        }

        if (!object->HasValidHandle())
        {
            SysPushErrorIO();
            return {};
        }

        return object;
    }

    static AuSPtr<IPCSharedMemory> GetFutexPagesFromCacheOrImport(const IPCToken &mem)
    {
        AU_LOCK_GUARD(gLock);

        auto id  = AuMakePair(mem.cookie, mem.pid);
        auto itr = gSharedViewCache.find(id);
        if (itr != gSharedViewCache.end())
        {
            auto test = itr->second.lock();
            if (test)
            {
                return test;
            }
        }

        auto shared = ImportSharedMemoryEx(mem);
        if (!shared)
        {
            SysPushErrorNested();
            return {};
        }

        if (!AuTryInsert(gSharedViewCache, id, shared))
        {
            SysPushErrorMem();
            // We don't need to fail. We can leak next time. It'll be fine.
        }

        return shared;
    }

    AuSPtr<IPCMutexProxy> ImportMutexEx(const IPCToken &handle, const IPCToken &mem, AuUInt32 index)
    {
        int fd {-1};
        if (!IO::UNIX::FDAccept(handle, fd))
        {
            SysPushErrorNested();
            return {};
        }

        auto view = GetFutexPagesFromCacheOrImport(mem);
        if (!view)
        {
            SysPushErrorNested();
            return {};
        }

        auto object = AuMakeShared<IPCMutexProxy>(fd, view, index);
        if (!object)
        {
            SysPushErrorMem();
            ::close(fd);
            return {};
        }

        if (!object->HasValidHandle())
        {
            SysPushErrorIO();
            return {};
        }

        return object;
    }

    AUKN_SYM AuSPtr<IPCMutex> ImportMutex(const AuString &handle)
    {
        IPC::IPCHandle decodedHandle;

        if (!decodedHandle.FromString(handle))
        {
            SysPushErrorParseError("Invalid handle: {}", handle);
            return {};
        }

        auto val = decodedHandle.GetToken(IPC::EIPCHandleType::eIPCPrimitiveMutex, 0);
        if (!val)
        {
            SysPushErrorParseError("Invalid handle: {}", handle);
            return {};
        }

        auto mem = decodedHandle.GetToken(IPC::EIPCHandleType::eIPCMemory, 1);
        if (!mem)
        {
            SysPushErrorParseError("Invalid handle: {}", handle);
            return {};
        }

        return ImportMutexEx(val->token, mem->token, val->token.word);
    }
}