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

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

#include <sys/syscall.h>
#include <linux/futex.h>

#if !defined(_AURUNTIME_GENERIC_SEMAPHORE)
#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);
    }

    Semaphore::Semaphore(long intialValue) : value_(intialValue)
    {

    }
    
    Semaphore::~Semaphore()
    {
    }

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

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

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

        errno = 0;

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

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

        auto old = this->value_;
             //!tryLock (with old in a scope we can access)
        while (!((old != 0) &&
                 (AuAtomicCompareExchange(&this->value_, old - 1, old) == old)))
        {
            if (uTimeout != 0)
            {
                uStart = Time::SteadyClockNS();
                if (uStart >= uEnd)
                {
                    return false;
                }

                int ret {};
                do
                {
                    ret = futex_wait(&this->value_, 0, &tspec);
                }
                while (ret == EINTR);
            }
            else
            {
                int ret {};
                bool bStatus {};

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

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

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

            old = this->value_;
        }

        return true;
    }
    
    void Semaphore::Lock()
    {
        auto status = Lock(0);
        SysAssert(status, "Couldn't lock semaphore");
    }
    
    void Semaphore::Unlock(long count)
    {
        AuAtomicAdd<AuUInt32>(&this->value_, count);
        futex_wake(&this->value_, count);
    }
    
    void Semaphore::Unlock()
    {
        Unlock(0);
    }
    
    AUKN_SYM ISemaphore *SemaphoreNew(int iInitialCount)
    {
        return _new Semaphore(iInitialCount);
    }

    AUKN_SYM void SemaphoreRelease(ISemaphore *pSemaphore)
    {
        AuSafeDelete<Semaphore *>(pSemaphore);
    }
}
#endif