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

    File: AuMutex.Linux.cpp
    Date: 2022-12-28
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "AuMutex.Generic.hpp"

#include <sys/syscall.h>
#include <linux/futex.h>
#include "SMPYield.hpp"

#if !defined(_AURUNTIME_GENERIC_MUTEX)
#include <Source/Time/Time.hpp>
        
namespace Aurora::Threading::Primitives
{
    static int futex(uint32_t *uaddr, int futex_op, uint32_t val,
                     const struct timespec *timeout, 
                     uint32_t *uaddr2, uint32_t val3)
    {
        return syscall(SYS_futex, uaddr, futex_op, val, timeout, uaddr2, val3);
    }

    static int futex_wait(uint32_t *addr, uint32_t expected)
    {
        return futex(addr, FUTEX_WAIT, expected, 0, 0, 0);
    }

    static int futex_wait(uint32_t *addr, uint32_t expected, const struct timespec *timeout)
    {
        if (timeout)
        {
            return futex(addr, FUTEX_WAIT_BITSET, expected, timeout, 0, FUTEX_BITSET_MATCH_ANY);
        }
        else
        {
            return futex(addr, FUTEX_WAIT, expected, timeout, 0, 0);
        }
    }

    static int futex_wake(uint32_t *addr, uint32_t nthreads)
    {
        return futex(addr, FUTEX_WAKE, nthreads, 0, 0, 0);
    }

    Mutex::Mutex()
    {

    }
    
    Mutex::~Mutex()
    {

    }

    bool Mutex::HasOSHandle(AuMach &mach)
    {
        return false;
    }
    
    bool Mutex::HasLockImplementation()
    {
        return true;
    }
    
    bool Mutex::TryLock()
    {
        return DoTryIf([=]()
        {
            auto old = this->value_;
            return (old == 0 && AuAtomicCompareExchange<AuUInt32>(&this->value_, 1, old) == old);
        });
    }

    bool Mutex::Lock(AuUInt64 uTimeout)
    {
        return LockNS(AuMSToNS<AuUInt64>(uTimeout));
    }

    bool Mutex::LockNS(AuUInt64 uTimeout)
    {
        if (this->TryLock())
        {
            return true;
        }

        AuUInt64 uStart = AuTime::SteadyClockNS();
        AuUInt64 uEnd = uStart + uTimeout;

        struct timespec tspec;
        if (uTimeout != 0)
        {
            Time::auabsns2ts(&tspec, uEnd);
        }

        auto state = this->value_;
        while (!(state == 0 && AuAtomicCompareExchange<AuUInt32>(&this->value_, 1, state) == state))
        {
            if (uTimeout != 0)
            {
                uStart = Time::SteadyClockNS();
                if (uStart >= uEnd)
                {
                    return false;
                }

                int ret {};
                do
                {
                    ret = futex_wait(&this->value_, state, &tspec);
                }
                while (ret == EINTR);
            }
            else
            {
                int ret {};
                bool bStatus {};

                do
                {
                    if ((ret = futex_wait(&this->value_, state)) == 0)
                    {
                        bStatus = true;
                        break;
                    }

                    if (ret == EAGAIN || errno == EAGAIN)
                    {
                        bStatus = true;
                        break;
                    }
                    
                }
                while (ret == EINTR);

                RUNTIME_ASSERT_SHUTDOWN_SAFE(bStatus, "Mutex wait failed: {}", ret)
            }

            state = this->value_;
        }

        return true;
    }
    
    void Mutex::Lock()
    {
        auto status = Lock(0);
        SysAssert(status, "Couldn't lock mutex");
    }
    
    void Mutex::Unlock()
    {
        this->value_ = 0;
        futex_wake(&this->value_, 1);
    }
    
    AUKN_SYM IWaitable *MutexNew()
    {
        return _new Mutex();
    }

    AUKN_SYM void MutexRelease(IWaitable *pMutex)
    {
        AuSafeDelete<Mutex *>(pMutex);
    }
}
#endif