/* EU DST example */
/* version 2: dd 23-10-2024 */

// The RTC is kept in local winter time (standard time). This approach is key for the simplicity of this solution.
// This code is for a DST from Last sunday in March 1:00 local time until Last sunday in October 3:00 local time. This can be changed if required.

#include <RTClib.h>   // https://github.com/adafruit/rtclib 
RTC_DS3231 rtc; 
//RTC_DS1307 rtc;

#define USEDST  true // Use DST (true or false)

DateTime now; 

DateTime dstclock(DateTime n) { // Return the given (DST adjusted) date and time according to DST settings (for extensive date and time calculations)
  
  DateTime b, e;
  
  b = DateTime(n.year(), 3, 31, 3, 0, 0); b = DateTime(n.year(), 3, 31 - b.dayOfTheWeek(), 1, 0, 0); // Last sunday in march 1:00
  e = DateTime(n.year(), 10, 31, 3, 0, 0); e = DateTime(n.year(), 10, 31 - e.dayOfTheWeek(), 3, 0, 0); // Last sunday in October 3:00

  if (USEDST && (n > b) && (n < e)) n = n + TimeSpan(0,1,0,0); // adjust to standard time if within summertime
  return n;
}; 

DateTime getclock() { // Retrieve the (DST adjusted) date and time
  
  DateTime n, b, e;
  
  n = rtc.now();
  b = DateTime(n.year(), 3, 31, 3, 0, 0); b = DateTime(n.year(), 3, 31 - b.dayOfTheWeek(), 1, 0, 0); // Last sunday in March 1:00
  e = DateTime(n.year(), 10, 31, 3, 0, 0); e = DateTime(n.year(), 10, 31 - e.dayOfTheWeek(), 3, 0, 0); // Last sunday in October 3:00

  if (USEDST && (n > b) && (n < e)) n = n + TimeSpan(0,1,0,0); // adjust to standard time if within summertime
  return n;
}; 

void setclock(DateTime n) { // if the clock is set during summertime then adjust the clock to standard time

  if (USEDST && (n != dstclock(n)) n = n - TimeSpan(0,1,0,0); // if summertime then adjust to the standard time 
  rtc.adjust(n); // Set the clock to standard time
}; 

void setup() {
  // initialise the rtc 
  rtc.begin();
//  if (rtc.lostPower())  setclock(DateTime(F(__DATE__), F(__TIME__))); // Set date and time for use with the DS3231 RTC
  if (!rtc.isrunning()) setclock(DateTime(F(__DATE__), F(__TIME__))); // Set date and time for use with the DS1307 RTC
}

void loop() {
  now = getclock(); // read the time from the RTC and adjust for DST or
  now = dstclock(rtc.now()); // read the time from the RTC and adjust for DST and do date/time calculations
}