timecore.lua

-- As we are located in central europe, we have GMT+1

--Summer winter time convertion
--See: https://arduinodiy.wordpress.com/2015/10/13/the-arduino-and-daylight-saving-time/
--
--As October has 31 days, we know that the last Sunday will always fall from the 25th to the 31st
--So our check at the end of daylight saving will be as follows:
--if (dow == 7 && mo == 10 && d >= 25 && d <=31 && h == 3 && DST==1)
--{
--setclockto 2 am;
--DST=0;
--}
--
--To start summertime/daylightsaving time on the last Sunday in March is mutatis mutandis the same:
--if (dow == 7 && mo == 3 && d >= 25 && d <=31 && h ==2 && DST==0)
--{
--setclockto 3 am;
--DST=1;
--}

local function getSummerTime(year, month, day, hours, minutes, seconds,dow)

  -- we are in 100% in the summer time
  if (month > 3 and month < 10) then 
    return true
  -- March is not 100% Summer time, only starting at the last sunday
  elseif ((month == 3 and day >= 25 and day <= 31 and hours > 2 and dow == 7) or
          -- Only handle days after the last sunday in this month
          ((month == 3 and day >= 25 and day <= 31 and dow < 7 and ((7-dow + day) > 31))) ) then
   -- set summer time
   return true
  -- October is not 100% Summer time, ending with the last sunday
  elseif ((month == 10 and day >= 25 and day <= 31 and hours <= 2 and dow == 7) or
          (month == 10 and day >= 25 and day <= 31 and dow < 7 and ((7-dow + day) <= 31)) or 
           -- Handle all days up to the 25. of october
           (month == 10 and day < 25 )
           ) then
   -- set summer time
   return true
  end
  return false
end


---------------------------------------------------------
-- Here comes some code to extract the year, month, day, hour, minute, second and day of week of a unix timestamp

-- Source:
-- http://www.jbox.dk/sanos/source/lib/time.c.html

YEAR0=1900

EPOCH_YR=1970
--SECS_DAY=(24L * 60L * 60L)
SECS_DAY=86400

ytab = {}
ytab[0] = {}
ytab[1] = {}
ytab[0][0] = 31
ytab[0][1] = 28
ytab[0][2] = 31
ytab[0][3] = 30
ytab[0][4] = 31
ytab[0][5] = 30
ytab[0][6] = 31
ytab[0][7] = 31
ytab[0][8] = 30
ytab[0][9] = 31
ytab[0][10] = 30
ytab[0][11] = 31
ytab[1][0] =  31
ytab[1][1] = 29
ytab[1][2] = 31
ytab[1][3] = 30
ytab[1][4] = 31
ytab[1][5] = 30
ytab[1][6] = 31
ytab[1][7] = 31
ytab[1][8] = 30
ytab[1][9] = 31
ytab[1][10] = 30
ytab[1][11] = 31

local leapyear = function(year)
    return  ( not ((year) % 4 ~= 0) and (((year) % 100 ~= 0) or not ((year) % 400 ~= 0)))
end

yearsize = function(year)
 if leapyear(year) then
  return 366
 else
  return 365
 end
end

local gettime = function(unixtimestmp)
  local year = EPOCH_YR
  local dayclock = math.floor(unixtimestmp % SECS_DAY)
  local dayno = math.floor(unixtimestmp / SECS_DAY)

  local sec = dayclock % 60
  local min = math.floor( (dayclock % 3600) / 60)
  local hour = math.floor(dayclock / 3600)
  local wday = math.floor( (dayno + 4) % 7) -- Day 0 was a thursday

  while (dayno >= yearsize(year))
  do
    dayno = dayno - yearsize(year);
    year=year + 1
  end
  local yday = dayno
  local mon = 0
  while (dayno >= ytab[leapyear(year) and 1 or 0][mon])
  do
     dayno = dayno - ytab[leapyear(year) and 1 or 0][mon];
      mon = mon + 1
   end
   mday = dayno + 1

  return year, mon +1 , mday, hour, min, sec, wday
end

getLocalTime = function(unixtimestmp,timezoneoffset)
  local localtime_year, localtime_month, localtime_day, localtime_hours, localtime_minutes, localtime_seconds, localtime_wday = gettime(unixtimestmp + timezoneoffset * 3600)
  if (getSummerTime(localtime_year, localtime_month, localtime_day, localtime_hours, localtime_minutes, localtime_seconds, localtime_wday)) then
    localtime_year, localtime_month, localtime_day, localtime_hours, localtime_minutes, localtime_seconds, localtime_wday = gettime(unixtimestmp + timezoneoffset * 3600 + 3600)
  end
  return {
      year = localtime_year,
      month = localtime_month,
      day = localtime_day,
      hours = localtime_hours,
      minutes = localtime_minutes < 10 and "0" .. localtime_minutes or localtime_minutes,
      seconds = localtime_seconds < 10 and "0" .. localtime_seconds or localtime_seconds
   }

end