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

    File: AuClock.cpp
    Date: 2021-6-13
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "AuClock.hpp"
#include "Time.hpp"


#if defined(AURORA_IS_MODERNNT_DERIVED)

// TODO (Reece): ....

// benchmarking:
// https://github.com/microsoft/STL/issues/2085
struct steady_clock_fast
{ // wraps QueryPerformanceCounter
    using rep = long long;
    using period = std::nano;
    using duration = std::chrono::nanoseconds;
    using time_point = _CHRONO time_point<steady_clock_fast>;
    static constexpr bool is_steady = true;

    _NODISCARD static time_point now() noexcept
    { // get current time
        static const long long _Freq = _Query_perf_frequency(); // doesn't change after system boot
        const long long _Ctr = _Query_perf_counter();
        static_assert(period::num == 1, "This assumes period::num == 1.");
        // Instead of just having "(_Ctr * period::den) / _Freq",
        // the algorithm below prevents overflow when _Ctr is sufficiently large.
        // It assumes that _Freq * period::den does not overflow, which is currently true for nano period.
        // It is not realistic for _Ctr to accumulate to large values from zero with this assumption,
        // but the initial value of _Ctr could be large.
        // 10 MHz is a very common QPC frequency on modern PCs. Optimizing for
        // this specific frequency can double the performance of this function by
        // avoiding the expensive frequency conversion path.
        if (_Freq == 10000000)
        {
            return time_point(duration(_Ctr * 100));
        }
        else
        {
            const long long _Whole = (_Ctr / _Freq) * period::den;
            const long long _Part = (_Ctr % _Freq) * period::den / _Freq;
            return time_point(duration(_Whole + _Part));
        }
    }
};

// ~3.0741 seconds
using high_res_clock = steady_clock_fast;

// holy fuck, we're keeping this
// ~2x improvement

#else

// ~6.07 seconds
using high_res_clock = std::chrono::high_resolution_clock;

#endif

#if defined(AURORA_IS_POSIX_DERIVED)
    #include <sys/resource.h>
#endif

using sys_clock = std::chrono::system_clock;
using steady_clock = std::chrono::steady_clock;

#if defined(AURORA_PLATFORM_WIN32)
    #define timegm _mkgmtime
#endif

static sys_clock::duration gEpoch;
static sys_clock::duration gUnixDelta;

static auto InitEpoch()
{
    std::tm start{0, 15, 10, 29, 7, 101, 0, 0, 0};
    auto epoch = sys_clock::from_time_t(timegm(&start)).time_since_epoch();

    std::tm unixStart{};
    unixStart.tm_mday = 1;
    unixStart.tm_year = 70;

    // dont care what the spec says, you can't trust some ms stls
    // sys_clock can have its own epoch for all we care
    auto nixEpoch = sys_clock::from_time_t(timegm(&unixStart)).time_since_epoch();

    gUnixDelta = epoch - nixEpoch;
    gEpoch = epoch;
    return 0;
}

static auto ___ = InitEpoch();

template<typename T>
static inline T NormalizeEpoch(T sysEpoch)
{
    return sysEpoch - gEpoch;
}

template<typename T>
static inline T DecodeEpoch(T auroraEpoch)
{
    return auroraEpoch + gEpoch;
}

template<typename Clock_t, typename Duration_t>
static auto TimeFromDurationSinceEpoch(Duration_t in)
{
    auto duration = std::chrono::duration_cast<typename Clock_t::duration>(in);
    return std::chrono::time_point<Clock_t>(DecodeEpoch(duration));
}

template<typename Duration_t>
static time_t CalculateTimeT(AuUInt64 in)
{
    return sys_clock::to_time_t(TimeFromDurationSinceEpoch<sys_clock>(Duration_t(in)));
}

namespace Aurora::Time
{
    // removed from public header / deprecating
    AUKN_SYM AuUInt64 HighResClock();
    AUKN_SYM AuUInt64 HighResClockNS();
    AUKN_SYM AuUInt64 HighResClockMS();
    AUKN_SYM AuUInt64 HighResClockJiffies();

    AUKN_SYM time_t SToCTime(AuInt64 time)
    {
        return CalculateTimeT<std::chrono::seconds>(time);
    }

    AUKN_SYM time_t NSToCTime(AuInt64 time)
    {
        return CalculateTimeT<std::chrono::nanoseconds>(time);
    }

    AUKN_SYM time_t MSToCTime(AuInt64 time)
    {
        return CalculateTimeT<std::chrono::milliseconds>(time);
    }

    AUKN_SYM AuInt64 CurrentClock()
    {
        return NormalizeEpoch(sys_clock::now().time_since_epoch()).count();
    }

    AUKN_SYM AuInt64 CurrentClockMS()
    {
        return std::chrono::duration_cast<std::chrono::milliseconds>(NormalizeEpoch(sys_clock::now().time_since_epoch())).count();
    }

    AUKN_SYM AuInt64 CurrentClockNS()
    {
        return std::chrono::duration_cast<std::chrono::nanoseconds>(NormalizeEpoch(sys_clock::now().time_since_epoch())).count();
    }

    AUKN_SYM AuUInt64 SteadyClock()
    {
    #if defined(AURORA_IS_MODERNNT_DERIVED)
        return _Query_perf_counter();
    #endif

        return SteadyClockNS() / (1000000000ull / SteadyClockJiffies());
    }

    AUKN_SYM AuUInt64 SteadyClockMS()
    {
    #if defined(AURORA_IS_POSIX_DERIVED)
        ::timespec spec {};
        if (::clock_gettime(CLOCK_MONOTONIC, &spec) == 0)
        {
            return AuSToMS<AuUInt64>(spec.tv_sec) + AuNSToMS<AuUInt64>(spec.tv_nsec);
        }
    #endif

    #if defined(AURORA_IS_MODERNNT_DERIVED)
        return std::chrono::duration_cast<std::chrono::milliseconds>(high_res_clock::now().time_since_epoch()).count();
    #endif

        return std::chrono::duration_cast<std::chrono::milliseconds>(steady_clock::now().time_since_epoch()).count();
    }

    AUKN_SYM AuUInt64 SteadyClockNS()
    {
    #if defined(AURORA_IS_POSIX_DERIVED)
        ::timespec spec {};
        if (::clock_gettime(CLOCK_MONOTONIC, &spec) == 0)
        {
            return AuMSToNS<AuUInt64>(AuSToMS<AuUInt64>(spec.tv_sec)) + (AuUInt64)spec.tv_nsec;
        }
    #endif

    #if defined(AURORA_IS_MODERNNT_DERIVED)
        return std::chrono::duration_cast<std::chrono::nanoseconds>(high_res_clock::now().time_since_epoch()).count();
    #endif

        return std::chrono::duration_cast<std::chrono::nanoseconds>(steady_clock::now().time_since_epoch()).count();
    }

    AUKN_SYM AuInt64 CTimeToMS(time_t time)
    {
        return std::chrono::duration_cast<std::chrono::milliseconds>(NormalizeEpoch(sys_clock::from_time_t(time).time_since_epoch())).count();
    }

    AuInt64 CTimeNSNormalize(AuUInt64 time)
    {
        return std::chrono::duration_cast<std::chrono::nanoseconds>(NormalizeEpoch(std::chrono::nanoseconds(time))).count();
    }

#if defined(AURORA_IS_POSIX_DERIVED)

    enum class EPseudoPosixClock
    {
        eUser,
        eKernel,
        eAll
    };

    static AuUInt64 GetPOSIXTimeEx(struct rusage *usage, EPseudoPosixClock e)
    {
        struct timeval *tv {};

        switch (e)
        {
        case EPseudoPosixClock::eAll:
        {
            return GetPOSIXTimeEx(usage, EPseudoPosixClock::eKernel) +
                GetPOSIXTimeEx(usage, EPseudoPosixClock::eUser);
        }
        case EPseudoPosixClock::eUser:
        {
            tv = &usage->ru_utime;
            break;
        }
        case EPseudoPosixClock::eKernel:
        {
            tv = &usage->ru_stime;
            break;
        }
        };

        auto uMS = AuSToMS<AuUInt64>(tv->tv_sec);
        auto uNS = AuMSToNS<AuUInt64>(uMS) +
            tv->tv_usec * 1'000ull;

        return uNS;
    }

    static AuUInt64 GetPOSIXTime(bool bThread, EPseudoPosixClock e)
    {
        struct rusage usage;

        getrusage(bThread ? RUSAGE_THREAD : RUSAGE_SELF,
                  &usage);

        return GetPOSIXTimeEx(&usage, e);
    }
    
    #if !defined(CLOCK_THREAD_CPUTIME_ID)
        #define CLOCK_THREAD_CPUTIME_ID 0
    #endif

    #if !defined(CLOCK_PROCESS_CPUTIME_ID)
        #define CLOCK_PROCESS_CPUTIME_ID 0
    #endif

#endif

#if defined(AURORA_IS_MODERNNT_DERIVED)    

#define ADD_CLOCK_FAMILY(fn, type, expr, posixId, posixCall)                                    \
    AUKN_SYM  AuUInt64 fn ## ClockJiffies();                                                    \
                                                                                                \
    AUKN_SYM AuUInt64 fn ## ClockMS()                                                           \
    {                                                                                           \
        return AuNSToMS<AuUInt64>(fn ## ClockNS());                                             \
    }                                                                                           \
                                                                                                \
    AUKN_SYM AuUInt64 fn ## ClockNS()                                                           \
    {                                                                                           \
        FILETIME creation, exit, kernel, user;                                                  \
        if (::Get ## type ## Times(GetCurrent ## type(), &creation, &exit, &kernel, &user))     \
        {                                                                                       \
            ULARGE_INTEGER ullUser;                                                             \
            {                                                                                   \
                ullUser.LowPart = user.dwLowDateTime;                                           \
                ullUser.HighPart = user.dwHighDateTime;                                         \
            }                                                                                   \
                                                                                                \
            ULARGE_INTEGER ullKernel;                                                           \
            {                                                                                   \
                ullKernel.LowPart = kernel.dwLowDateTime;                                       \
                ullKernel.HighPart = kernel.dwHighDateTime;                                     \
            }                                                                                   \
            return (expr) * 100ull;                                                             \
        }                                                                                       \
        return HighResClockNS();                                                                \
    }                                                                                           \
                                                                                                \
    AUKN_SYM AuUInt64 fn ## Clock()                                                             \
    {                                                                                           \
        FILETIME creation, exit, kernel, user;                                                  \
                                                                                                \
        if (::Get ## type ## Times(GetCurrent ## type(), &creation, &exit, &kernel, &user))     \
        {                                                                                       \
            ULARGE_INTEGER ullUser;                                                             \
            {                                                                                   \
                ullUser.LowPart = user.dwLowDateTime;                                           \
                ullUser.HighPart = user.dwHighDateTime;                                         \
            }                                                                                   \
                                                                                                \
            ULARGE_INTEGER ullKernel;                                                           \
            {                                                                                   \
                ullKernel.LowPart = kernel.dwLowDateTime;                                       \
                ullKernel.HighPart = kernel.dwHighDateTime;                                     \
            }                                                                                   \
            return expr;                                                                        \
        }                                                                                       \
                                                                                                \
        return fn ##ClockNS() / (1000000000ull / fn ## ClockJiffies());                         \
    }                                                                                           \
                                                                                                \
    AUKN_SYM AuUInt64 fn ## ClockJiffies()                                                      \
    {                                                                                           \
        return 1000000000ull / 100u;                                                            \
    }

#elif defined(AURORA_IS_POSIX_DERIVED)

#define ADD_CLOCK_FAMILY(fn, type, expr, posixId, posixCall)                                    \
    AUKN_SYM  AuUInt64 fn ## ClockJiffies();                                                    \
                                                                                                \
    AUKN_SYM AuUInt64 fn ## ClockMS()                                                           \
    {                                                                                           \
        if (!posixId)                                                                           \
        {                                                                                       \
            return AuNSToMS<AuUInt64>(GetPOSIXTime AU_WHAT(posixCall));                         \
        }                                                                                       \
        return AuNSToMS<AuUInt64>(fn ## ClockNS());                                             \
    }                                                                                           \
                                                                                                \
    AUKN_SYM AuUInt64 fn ## ClockNS()                                                           \
    {                                                                                           \
        if (!posixId)                                                                           \
        {                                                                                       \
            return GetPOSIXTime AU_WHAT(posixCall);                                             \
        }                                                                                       \
        ::timespec spec {};                                                                     \
        if (::clock_gettime(posixId, &spec) == 0)                                               \
        {                                                                                       \
            return AuMSToNS<AuUInt64>(AuSToMS<AuUInt64>(spec.tv_sec)) + (AuUInt64)spec.tv_nsec; \
        }                                                                                       \
        return HighResClockNS();                                                                \
    }                                                                                           \
                                                                                                \
    AUKN_SYM AuUInt64 fn ## Clock()                                                             \
    {                                                                                           \
        if (!posixId)                                                                           \
        {                                                                                       \
            return fn ##ClockNS() / 1000ull;                                                    \
        }                                                                                       \
        return fn ##ClockNS() / (1000000000ull / fn ## ClockJiffies());                         \
    }                                                                                           \
                                                                                                \
    AUKN_SYM AuUInt64 fn ## ClockJiffies()                                                      \
    {                                                                                           \
        if (!posixId)                                                                           \
        {                                                                                       \
            return 1'000'000ull;                                                                \
        }                                                                                       \
        static AuUInt64 frequency = 0;                                                          \
        if (frequency != 0)                                                                     \
        {                                                                                       \
            return frequency;                                                                   \
        }                                                                                       \
                                                                                                \
        ::timespec spec {};                                                                     \
        if (::clock_getres(posixId, &spec) == 0)                                                \
        {                                                                                       \
            if (spec.tv_nsec && !spec.tv_sec)                                                   \
            {                                                                                   \
                return frequency = 1000000000ull / spec.tv_nsec;                                \
            }                                                                                   \
            else                                                                                \
            {                                                                                   \
                SysUnreachable();                                                               \
                return 0;                                                                       \
            }                                                                                   \
        }                                                                                       \
                                                                                                \
        return HighResClockJiffies();                                                           \
    }

#else

    AUKN_SYM AuUInt64 fn ## ClockMS()
    {
        return 0;
    }

    AUKN_SYM AuUInt64 fn ## ClockNS()
    {
        return 0;
    }

    AUKN_SYM AuUInt64 fn ## Clock()
    {
        return 0;
    }

    AUKN_SYM AuUInt64 fn ## ClockJiffies()
    {
        return 0;
    }

#endif
    
    ADD_CLOCK_FAMILY(Process, Process, (ullUser.QuadPart + ullKernel.QuadPart), CLOCK_PROCESS_CPUTIME_ID, (false, EPseudoPosixClock::eAll));
    ADD_CLOCK_FAMILY(ProcessKernel, Process, (ullKernel.QuadPart), 0, (false, EPseudoPosixClock::eKernel));
    ADD_CLOCK_FAMILY(ProcessUser, Process, (ullUser.QuadPart), CLOCK_PROCESS_CPUTIME_ID, (false, EPseudoPosixClock::eUser));
    ADD_CLOCK_FAMILY(Thread, Thread, (ullUser.QuadPart + ullKernel.QuadPart), CLOCK_THREAD_CPUTIME_ID, (true, EPseudoPosixClock::eAll));
    ADD_CLOCK_FAMILY(ThreadKernel, Thread, (ullKernel.QuadPart), 0, (true, EPseudoPosixClock::eKernel));
    ADD_CLOCK_FAMILY(ThreadUser, Thread, (ullUser.QuadPart), CLOCK_THREAD_CPUTIME_ID, (true, EPseudoPosixClock::eUser));

    AUKN_SYM AuInt64 ConvertAuroraToUnixMS(AuInt64 in)
    {
        return std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::milliseconds(in) + gUnixDelta).count();
    }

    AUKN_SYM AuInt64 ConvertAuroraToUnixNS(AuInt64 in)
    {
        return std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::nanoseconds(in) + gUnixDelta).count();
    }

    AUKN_SYM AuInt64 ConvertUnixToAuroraMS(AuInt64 in)
    {
        return std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::milliseconds(in) - gUnixDelta).count();
    }

    AUKN_SYM AuInt64 ConvertUnixToAuroraNS(AuInt64 in)
    {
        return std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::nanoseconds(in) - gUnixDelta).count();
    }

    AUKN_SYM AuUInt64 SteadyClockJiffies()
    {
        static AuUInt64 frequency = 0;
        if (frequency != 0)
        {
            return frequency;
        }

    #if defined(AURORA_COMPILER_MSVC)
        return frequency = _Query_perf_frequency();
    #endif

    #if defined(AURORA_IS_POSIX_DERIVED)
        ::timespec spec {};
        if (::clock_getres(CLOCK_MONOTONIC, &spec) == 0)
        {
            if (spec.tv_nsec && !spec.tv_sec)
            {
                return frequency = 1000000000ull / spec.tv_nsec;
            }
        }
    #endif

        return frequency = static_cast<double>(steady_clock::period::den) / static_cast<double>(steady_clock::period::num);
    }

    AUKN_SYM tm ToCivilTime(AuInt64 time, bool UTC)
    {
        std::tm ret {};
        auto timet = MSToCTime(time);
        if (UTC)
        {
        #if defined(AURORA_COMPILER_MSVC)
            auto tm = gmtime_s(&ret, &timet);
        #else
            auto tm = gmtime_r(&timet, &ret);
        #endif
        #if defined(AURORA_COMPILER_MSVC)
            SysAssert(!tm, "couldn't convert civil time");
        #else
            SysAssert(tm, "couldn't convert civil time");
        #endif

        }
        else
        {
        #if defined(AURORA_COMPILER_MSVC)
            if (localtime_s(&ret, &timet))
        #else
            if (!localtime_r(&timet, &ret))
        #endif
            {
                SysPushErrorGeneric("Couldn't convert local civil time");
                return ToCivilTime(time, true);
            }
        }
        tm _;
        _.CopyFrom(ret);
        return _;
    }

    AUKN_SYM AuInt64 FromCivilTime(const tm &time, bool UTC)
    {
        ::tm tm;
        time_t timet;

        time.CopyTo(tm);

        if (UTC)
        {
            tm.tm_isdst = 0;
            timet = timegm(&tm);
        }
        else
        {
            tm.tm_isdst = -1; // out of the 2 crts i've bothered to check, out of 3, this is legal
            timet = mktime(&tm);
        }

        if ((timet == 0) || (timet == -1))
        {
            return 0;
        }

        return std::chrono::duration_cast<std::chrono::milliseconds>(NormalizeEpoch(std::chrono::system_clock::from_time_t(timet).time_since_epoch())).count();
    }

    AUKN_SYM tm NormalizeCivilTimezone(const Time::tm &time, ETimezoneShift shift)
    {
        if ((time.tm_isdst == 0) && (shift == ETimezoneShift::eUTC))
        {
            return time;
        }

        return ToCivilTime(FromCivilTime(time, shift == ETimezoneShift::eUTC));
    }

#pragma region TO_DEPRECATE
    // [soon to be] @deprecated / was used by benchmarks to measure thread time

    AUKN_SYM AuUInt64 HighResClock()
    {
        return SteadyClock();
    }

    AUKN_SYM AuUInt64 HighResClockMS()
    {
        return SteadyClockMS();
    }

    AUKN_SYM AuUInt64 HighResClockNS()
    {
        return SteadyClockNS();
    }

    AUKN_SYM AuUInt64 HighResClockJiffies()
    {
        return SteadyClockJiffies();
    }

#pragma endregion TO_DEPRECATE
}