/**
There is no weekday calculatation.
If it hits the month it automaticly go to dst or std time

This example use los angeles time 
**/

#include <Wire.h>

//BEGIN RTC CODE

//rtc variables
static int second, minute, hour;
static int dayOfWeek, dayOfMonth, month, year;
//end rtc variables

#define DS3231_I2C_ADDRESS 0x68

byte decToBcd(byte val) {
  return ( (val / 10 * 16) + (val % 10) );
}

// Convert binary coded decimal to decimal numbers
byte bcdToDec(byte val) {
  return ( (val / 16 * 10) + (val % 16) );
}

// Set the time
void rtc_setTime(byte second, byte minute, byte hour, byte wday, byte mday, byte mon, byte year) {
  // sets time and date data to DS3231
  Wire.beginTransmission(DS3231_I2C_ADDRESS);
  Wire.write(0); // set next input to start at the seconds register
  Wire.write(decToBcd(second)); // set seconds
  Wire.write(decToBcd(minute)); // set minutes
  Wire.write(decToBcd(hour)); // set hours

  Wire.write(decToBcd(wday)); // set day of week (1=Monday, 7=Sunday)
  Wire.write(decToBcd(mday)); // set date (1 to 31)
  Wire.write(decToBcd(mon)); // set month
  Wire.write(decToBcd(year)); // set year (0 to 99)
  
  Wire.endTransmission();
}

//Refresh/Read the time
void rtc_readTime() {
  Wire.beginTransmission(DS3231_I2C_ADDRESS);
  Wire.write(0); // set DS3231 register pointer to 00h
  Wire.endTransmission();

  // request seven bytes of data from DS3231 starting from register 00h
  Wire.requestFrom(DS3231_I2C_ADDRESS, 7);
  second = bcdToDec(Wire.read() & 0x7f);
  minute = bcdToDec(Wire.read());
  hour = bcdToDec(Wire.read() & 0x3f);
  dayOfWeek = bcdToDec(Wire.read());
  dayOfMonth = bcdToDec(Wire.read());
  month = bcdToDec(Wire.read());
  year = bcdToDec(Wire.read());

  //leap year correction (if year is > 2100)
  #define LEAP_YEAR(Y)     ( !(((Y))%4) && ( (((Y))%100) || !(((Y))%400) ) )

  if(LEAP_YEAR(year) == 0 && dayOfMonth == 29 && month == 2){
    rtc_setTime(second, minute, hour, dayOfWeek, 1, 3, year);
  }
}

void rtc_init(){
  Wire.begin(); 
}

//END RTC CODE


//BEGIN DST CODE

static int32_t __offset = 0L; //rtc offst
static int32_t __local = 0l; //local offset
static int32_t __dst;
static bool _dst;

//get the offset from rtc (set this to 0 if the rtc is utc/gmt time)
void rtc_offset(int32_t seconds){
  __offset = seconds;
}

//set the user local offset (set this to 0 if you is utc/gmt time)
void set_local_offset(int32_t seconds){
  __local = seconds;
}

//just gets the month days
int16_t getYeardayMonth(int16_t month, long currentYear){
  
  int monthlist[12] = {1, 32, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335};
  int monthlistleap[12] = {1, 32, 61, 92, 122, 153, 183, 214, 245, 275, 306, 336};

  int16_t days = 0;

  if( !(((currentYear))%4) && ( (((currentYear))%100) || !(((currentYear))%400) ) ){
    days = monthlistleap[month -1];
  } else {
    days = monthlist[month -1];
  }
   
  return days;
}

int8_t getWeekYday(int yday, long year){
  int total = 0;
    
  for(int i = 0; i < year; i++){
    total = i * 365;
    if(LEAP_YEAR(i)){
      total++;
    }
  }
  total+=yday;
  return (total+6)%7;
}
//sets the dst (you need to add current rtc month and weekday) sunday is 0
void set_dst(long currentYear, int currentMonth, int currentDay, int sweekday, int smonth, int eday, int emonth, int offset){
  __dst = offset;
  
  const uint8_t daysInMonth[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

  uint16_t days = currentDay, endMonth, startMonth; 

  for (uint8_t i = 1; i < currentMonth; i++)
  {
    days += daysInMonth[i - 1];
  }
  if (currentMonth > 2 && !(((currentYear))%4) && ( (((currentYear))%100) || !(((currentYear))%400) ) )
  {
    days++;
  }

  startMonth = getYeardayMonth(smonth, currentYear);
  endMonth = getYeardayMonth(emonth, currentYear);

  if(days > startMonth && days < endMonth){
    _dst = 1;
  } else {
    _dst = 0;
  }

  if(days > endMonth){
    _dst = 0;
  }

  if(days < startMonth){
    _dst = 0;
  }

}

//gets the local offset with dst
int32_t get_local_offset(){
  if(_dst){
    return __local + __dst;
  } else {
    return __local;
  }
}

//END DST CODE
void setup() {
  rtc_init();

  //set your offset here in seconds
  rtc_offset(-28800);
  set_local_offset(-28800);
  Serial.begin(115200);
}

void loop() {
  rtc_readTime();
  static char buf[50];
  sprintf(buf, "%u-%02d-%02dT%02d:%02d:%02dZ", year, month, dayOfMonth, hour, minute, second); 
  set_dst(year, month, dayOfMonth, 0, 3, 0, 11, 3600);
  Serial.println(buf);
  Serial.println(get_local_offset()); //in seconds
  delay(500);
}