Time

pub const Time = extern struct {
    /// 1900 - 9999
    year: u16,

    /// 1 - 12
    month: u8,

    /// 1 - 31
    day: u8,

    /// 0 - 23
    hour: u8,

    /// 0 - 59
    minute: u8,

    /// 0 - 59
    second: u8,

    _pad1: u8,

    /// 0 - 999999999
    nanosecond: u32,

    /// The time's offset in minutes from UTC.
    /// Allowed values are -1440 to 1440 or unspecified_timezone
    timezone: i16,
    daylight: packed struct(u8) {
        /// If true, the time has been adjusted for daylight savings time.
        in_daylight: bool,

        /// If true, the time is affected by daylight savings time.
        adjust_daylight: bool,

        _: u6,
    },

    _pad2: u8,

    comptime {
        std.debug.assert(@sizeOf(Time) == 16);
    }

    /// Time is to be interpreted as local time
    pub const unspecified_timezone: i16 = 0x7ff;

    fn daysInYear(year: u16, max_month: u4) u9 {
        var days: u9 = 0;
        var month: u4 = 0;
        while (month < max_month) : (month += 1) {
            days += std.time.epoch.getDaysInMonth(year, @fromBackingInt(@intCast(month + 1)));
        }
        return days;
    }

    pub fn toEpoch(self: std.os.uefi.Time) u64 {
        var year: u16 = 0;
        var days: u32 = 0;

        while (year < (self.year - 1971)) : (year += 1) {
            days += daysInYear(year + 1970, 12);
        }

        days += daysInYear(self.year, @as(u4, @intCast(self.month)) - 1) + self.day;
        const hours: u64 = self.hour + (days * 24);
        const minutes: u64 = self.minute + (hours * 60);
        const seconds: u64 = self.second + (minutes * std.time.s_per_min);
        return self.nanosecond + (seconds * std.time.ns_per_s);
    }
}