/***
    Copyright (C) 2021-2023 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: AuCivilTime.cpp
    File: AuClock.cpp
    Date: 2023-09-18
    Date: 2021-6-13
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "AuCivilTime.hpp"
#include "Time.hpp"


#if defined(AURORA_COMPILER_MSVC) || \
    defined(_CRT_USE_CONFORMING_ANNEX_K_TIME)

    #define TIME_MSFT_LIKE
    
#endif

#if defined(TIME_MSFT_LIKE)

    #define timegm _mkgmtime

#endif

using sys_clock = std::chrono::system_clock; // more stds to remove

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();

sys_clock::duration __NormalizeEpoch(sys_clock::duration sysEpoch)
{
    return sysEpoch - gEpoch;
}

sys_clock::duration __DecodeEpoch(sys_clock::duration auroraEpoch)
{
    return auroraEpoch + gEpoch;
}

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

template<typename Duration_t>
static time_t CalculateTimeT(AuUInt64 in)
{
    return sys_clock::to_time_t(TimeFromDurationSinceEpoch(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 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 tm ToCivilTime(AuInt64 time, ETimezoneShift shift)
    {
        std::tm ret {};
        auto timet = MSToCTime(time);
        if (shift == ETimezoneShift::eUTC)
        {
        #if defined(TIME_MSFT_LIKE)
            auto tm = gmtime_s(&ret, &timet);
        #else
            auto tm = gmtime_r(&timet, &ret);
        #endif
        #if defined(TIME_MSFT_LIKE)
            SysAssert(!tm, "couldn't convert civil time");
        #else
            SysAssert(tm, "couldn't convert civil time");
        #endif

        }
        else
        {
        #if defined(TIME_MSFT_LIKE)
            if (localtime_s(&ret, &timet))
        #else
            if (!localtime_r(&timet, &ret))
        #endif
            {
                SysPushErrorGeneric("Couldn't convert local civil time");
            #if 0
                SysPanic();
            #else
                return ToCivilTime(time, ETimezoneShift::eUTC);
            #endif
            }
        }
        tm _;
        _.CopyFrom(ret);
        return _;
    }

    AUKN_SYM AuInt64 FromCivilTime(const tm &time, ETimezoneShift shift)
    {
        ::tm tm;
        time_t timet;

        time.CopyTo(tm);

        if (shift == ETimezoneShift::eUTC)
        {
            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.isdst.ValueOr(-1) == 0) && (shift == ETimezoneShift::eUTC))
        {
            return time;
        }

        return ToCivilTime(FromCivilTime(time, shift));
    }
}