Timezone.h

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/****
 * Sming Framework Project - Open Source framework for high efficiency native ESP8266 development.
 * Created 2015 by Skurydin Alexey
 * http://github.com/SmingHub/Sming
 * All files of the Sming Core are provided under the LGPL v3 license.
 *
 * Timezone.h - Time Zone support library
 *
 * Original code (c) Jack Christensen Mar 2012
 * Arduino Timezone Library Copyright (C) 2018 by Jack Christensen and
 * licensed under GNU GPL v3.0, https://www.gnu.org/licenses/gpl.html
 *
 * @author mikee47 <mike@sillyhouse.net>
 * July 2018 Ported to Sming
 *
 ****/

#pragma once

#include <DateTime.h>

// convenient constants for TimeChangeRules
enum __attribute__((packed)) week_t {
    Last,
    First,
    Second,
    Third,
    Fourth,
};

enum __attribute__((packed)) dow_t {
    Sun = 0,
    Mon,
    Tue,
    Wed,
    Thu,
    Fri,
    Sat,
};

enum __attribute__((packed)) month_t {
    Jan = 1,
    Feb,
    Mar,
    Apr,
    May,
    Jun,
    Jul,
    Aug,
    Sep,
    Oct,
    Nov,
    Dec,
};

/*
 * Structure to describe rules for when daylight/summer time begins,
 * and when standard time begins
 */
struct TimeChangeRule {
    char tag[6];   
    week_t week;   
    dow_t dow;   
    month_t month; 
    uint8_t hour;  
    int offset; 
};

class Timezone
{
public:
    Timezone()
    {
    }

    Timezone(const TimeChangeRule& dstStart, const TimeChangeRule& stdStart)
    {
        init(dstStart, stdStart);
    }

    void init(const TimeChangeRule& dstStart, const TimeChangeRule& stdStart);

    time_t toLocal(time_t utc, const TimeChangeRule** p_tcr = nullptr);

    time_t toUTC(time_t local);

    bool utcIsDST(time_t utc);

    bool locIsDST(time_t local);

    const char* timeTag(bool isDst) const
    {
        return isDst ? dstRule.tag : stdRule.tag;
    }

    const char* utcTimeTag(time_t utc)
    {
        return timeTag(utcIsDST(utc));
    }

    const char* localTimeTag(time_t local)
    {
        return timeTag(locIsDST(local));
    }

private:
    /*
     * Calculate the DST and standard time change points for the given
     * given year as local and UTC time_t values.
     */
    void calcTimeChanges(unsigned yr);

    /*
     * Convert the given time change rule to a time_t value for the given year.
     */
    time_t toTime_t(TimeChangeRule r, unsigned yr);

private:
    TimeChangeRule dstRule = {"DST", First, Sun, Jan, 1, 0}; 
    TimeChangeRule stdRule = {"UTC", First, Sun, Jan, 1, 0}; 
    time_t dstStartUTC = 0;                                  
    time_t stdStartUTC = 0;                                  
    time_t dstStartLoc = 0;                                  
    time_t stdStartLoc = 0; 
};