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

    File: AuClock.cpp
    Date: 2021-6-13
    Author: Reece
    Note: Screw it, std::chrono has been widly shilled at C++11s answer to all these painful macros, asm linkage, and all the other bullshit that pulling clock counters entails.
          Semantics can and will continue to change over time. I remember when, in 2016 or something like that, msvcs implementation of chrono kept changing in minor ways.

          However, every platform that remotely pretends to support a C++ toolchain has a chrono high performance clock, and any PC-like platform that uses clang and C++ more than likely uses a vendor hacked liblibc++ stl.
          The following should be portable enough. Worst case scenario, you're on a platform with a platform-specific high res clock function you could hack into here alongside portable timezone-unaware timegm/mktime functions linked somewhere else.
          
          There is so much quirky shit one has to deal with when relying on timestamp/cycle counters  (cycle to ~time pred, plus positive delta, sometimes inlined assembly), it's just not worth it to
          implement a CNTVCT_EL0 / RDSC / related interface ourselves.

          I'll wave the white flag and use the STL in here for.now
***/
#include <Source/RuntimeInternal.hpp>
#include "AuClock.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

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
{
    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()
    {
        return SteadyClockNS();
    }

    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();
    }

    AUKN_SYM AuUInt64 HighResClock()
    {
        return high_res_clock::now().time_since_epoch().count();
    }

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

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

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

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

    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 ConvertInternalToAuroraEpochMS(AuUInt64 in)
    {
        static AuInt64 epochDelta = 0;

        if (epochDelta == 0)
        {
            epochDelta = CurrentClockMS() - HighResClockMS();
        }

        return epochDelta + in;
    }

    AUKN_SYM AuUInt64 ConvertInternalToAuroraEpochNS(AuUInt64 in)
    {
        static AuInt64 epochDelta = 0;

        if (epochDelta == 0)
        {
            epochDelta = CurrentClockNS() - HighResClockNS();
        }

        return epochDelta + in;
    }

    AUKN_SYM double CPUFrequencyDeltaNS()
    {
        static double frequency = 0;
        if (frequency != 0)
        {
            return frequency;
        }
        return frequency = (static_cast<double>(high_res_clock::period::num) / static_cast<double>(high_res_clock::period::den) * 1'000'000'000.f);
    }

    AUKN_SYM double CPUFrequencyDeltaMS()
    {
        static double frequency = 0;
        if (frequency != 0)
        {
            return frequency;
        }
        return frequency = (static_cast<double>(high_res_clock::period::num) / static_cast<double>(high_res_clock::period::den) * 1'000.f);
    }

    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 AuUInt64 HighResClockJiffies()
    {
        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_PROCESS_CPUTIME_ID, &spec) == 0)
        {
            if (spec.tv_nsec && !spec.tv_sec)
            {
                return frequency = 1000000000ull / spec.tv_nsec;
            }
        }
    #endif

        return frequency = static_cast<double>(high_res_clock::period::den) / static_cast<double>(high_res_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
            {
                AuLogWarn("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));
    }
}