time_zone_offset_conversions.hpp

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// SPDX-License-Identifier: MIT
#pragma once
#ifndef TIME_SHIELD_HEADER_CONVERSIONS_TIME_ZONE_OFFSET_CONVERSIONS_HPP_INCLUDED
#define TIME_SHIELD_HEADER_CONVERSIONS_TIME_ZONE_OFFSET_CONVERSIONS_HPP_INCLUDED
 
 
#include <time_shield/core.hpp>
 
namespace time_shield {
 
 
    template<class T = TimeZoneStruct>
    inline T to_time_zone(tz_t offset) {
        const int64_t off = static_cast<int64_t>(offset);
        const int64_t abs_val = (off < 0) ? -off : off;
 
        T tz;
        tz.hour = static_cast<decltype(tz.hour)>(abs_val / static_cast<int64_t>(SEC_PER_HOUR));
        tz.min  = static_cast<decltype(tz.min)>(
            (abs_val % static_cast<int64_t>(SEC_PER_HOUR)) / static_cast<int64_t>(SEC_PER_MIN)
        );
        tz.is_positive = (off >= 0);
        return tz;
    }
 
    template<class T>
    TIME_SHIELD_CONSTEXPR inline tz_t to_tz_offset(const T& tz) noexcept {
        const int sign = tz.is_positive ? 1 : -1;
        const int64_t sec = static_cast<int64_t>(tz.hour) * SEC_PER_HOUR
                          + static_cast<int64_t>(tz.min)  * SEC_PER_MIN;
        return static_cast<tz_t>(sign * sec);
    }
 
    TIME_SHIELD_CONSTEXPR inline tz_t tz_offset_hm(int hour, int min = 0) noexcept {
        const int sign = (hour < 0) ? -1 : 1;
        const int64_t ah = (hour < 0) ? -static_cast<int64_t>(hour) : static_cast<int64_t>(hour);
        const int64_t am = (min  < 0) ? -static_cast<int64_t>(min)  : static_cast<int64_t>(min);
        return static_cast<tz_t>(sign * (ah * SEC_PER_HOUR + am * SEC_PER_MIN));
    }
 
    TIME_SHIELD_CONSTEXPR inline bool is_valid_tz_offset(tz_t off) noexcept {
        // conservative range: [-12:00, +14:00]
        return off % 60 == 0
            && off >= -12 * SEC_PER_HOUR
            && off <=  14 * SEC_PER_HOUR;
    }
 
 
}; // namespace time_shield
 
#endif // TIME_SHIELD_HEADER_CONVERSIONS_TIME_ZONE_OFFSET_CONVERSIONS_HPP_INCLUDED