AuroraRuntime/Include/Aurora/Time/TM.hpp

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

    File: TM.hpp
    Date: 2022-1-24
    Author: Reece
***/
#pragma once

namespace Aurora::Time
{
    // This type is intended for interoperability with ANSI c, the Aurora Epoch, and planned calendar APIs
    struct tm
    {
        int year {};                 // The absolute gregorian-calendar year
        int mon {};                  // Months since January

        int mday {};                 // Days since last month
        AuOptional<int> wday {};     // Days since Monday   [usually ignored]
        AuOptional<int> yday {};     // Days since January  [usually ignored]

        int hour {};                 // Hours since yesterday
        int min {};                  // Minutes since the hour
        int sec {};                  // Seconds since the minute
        
        AuOptionalEx<bool> isdst {};
        AuOptionalEx<int>  knownMinutesWest {};  // Known minutes west - this is the opposite of Linux's minutes east.
                                                 // RESERVED FOR FUTURE CALENDAR API
        
        template<typename Dest_t>
        void CopyTo(Dest_t &out) const
        {
            out.tm_sec  = sec;
            out.tm_min  = min;
            out.tm_hour = hour;
            out.tm_mday = mday + 1;
            out.tm_mon  = mon;

        #if 0
            if (year < 1900)
            {
                out.tm_year = 0;
            }
            else
        #endif
            {
                out.tm_year = year - 1900;
            }
            
            if (wday)
            {
                auto cur = wday.value();
                if (cur == 6) // ^1
                {
                    out.tm_wday = 0;
                }
                else
                {
                    out.tm_wday = cur + 1;
                }
            }
            else
            {
                out.tm_wday = -1;
            }

            out.tm_yday = yday.value_or(-1);

            if (!isdst.HasValue())
            {
                out.tm_isdst = -1;
            }
            else
            {
                out.tm_isdst = isdst.value();
            }
        }

        template<typename In_t>
        void CopyFrom(const In_t &in)
        {
            sec = in.tm_sec;
            min = in.tm_min;
            hour = in.tm_hour;
            mday = in.tm_mday - 1;
            mon = in.tm_mon;
            year = in.tm_year + 1900;

            if (in.tm_wday == 0) // ^1
            {
                wday = 6;
            }
            else
            {
                wday = in.tm_wday - 1;
            }
            
            if (sec > 59) // ^2
            {
                sec = 59;
            }

            yday = in.tm_yday;
            isdst = in.tm_isdst; // (dont normalize -1. it's a quirk of most modern CRTs we can exploit to easily solve the [user-input + how do i guess DST] issue)
                                 // (stupid c programs shouldn't be exploiting this anyway. assume all std::tm, ::tm, and similar types calling into us follow boolean logic)
        }

        inline void Update()
        { /* no-op for now. */ }

    private:
        friend struct TMIntlAccessor;
        AuUInt64 localization_[2] {}; 
        // reserved for uncommitted and experimental calendar APIs 
        // currently defined as:
        //     u64 uKnownAuroraEpoch
        //     u64 optCalendarType
        // 
        // Where calendar types are used to convert day orders of magnitude via the JDN offset by -12 hours, and then the remaining hours added back onto the day
        // If !optCalendarType && isdst.value() == true,  optCalendarType = gregorian / must be normalized
        // If !optCalendarType && isdst.value() == false, optCalendarType = gregorian
        // optCalendarType = ECalendarType, with gregorian being 0, NULL, and default initialized
        // With uKnownAuroraEpoch leaking in from relevant internal AuTime APIs, it should be possible to create perfect time-zone and duration add/substract APIs on top of this
        // We just need a means to go from uKnownAuroraEpoch to mday/yday/mon/year given the days in year, days in month, and week specific attributes of the calendar
        // Further locale specific detail can be provided by the instance of a generic abstract calendar
    };
}



// Malding about the ANSI c defintion of ::tm 
    // Note (1): We don't give a single solitary fuck about what ISO 8601 says nor the intentions of braindead boomers who thought there were 61 seconds to an hour (^2)...
    //           Sunday is not a weekday; it's apart of the week-END. No English speaker will disagree with this once we get past the obvious gaslighting attempts from NGOs and indoctrination institutions.
    //           In my estimation, it's every English speaker ever born after the Stuarts (17xxs+) versus a handful of CIA boys and the International Organization for Standardization.
    //           In my tradition of upholding da norf, we're sticking by the 19th century industrialized understanding of time.
    // [tm_]wday is now the day offset since Monday, not days since last week.
    // [tm_]mday is now the day offset since the beginning of the month, not the calendar number - that's to say we deviate from other impls by asserting these members are all offsets, not whatever some CIA fuckbuddies at ANSI said it is.
    // (^2): there isn't such a concept in *CIVIL* time; leap seconds are only in the concept of "academic/astronomy circlejerk time" that no sane person, language runtime, or physical clock has ever cared about, nevermind implemented properly.
    //       they are wholly irrelevant to the conversion between calendar systems, and there isn't any legitimate use for polling wall-time with leap-second precision. unless you are looking for an API to build your GPS transponder or an NTP library, leap seconds aren't a factor in anything.
    //       this is a c++ library, not a live feed to the bullshit ad-hoc announcements of the international earth rotation and reference service.