How do I convert seconds since Epoch to current date and time? - time

Question

I know I posted this a while ago, but I figured out the solution. I wrote this code for a game called Roblox, but I'm just posting the code here in case anyone else who has this same problem needs a solution. Anyways, here's the code:
outputTime = true -- true: will print the current time to output window. false: won't print time
createVariable = true -- true: creates variables under game.Lighting. false: won't create variables
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--DO NOT EDIT BELOW----------------------------------------------------------------------------
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if(createVariable) then
yearVar = Instance.new("IntValue", game.Lighting)
yearVar.Name = "Year"
yearVar.Value = 0
monthVar = Instance.new("IntValue", game.Lighting)
monthVar.Name = "Month"
monthVar.Value = 0
dayVar = Instance.new("IntValue", game.Lighting)
dayVar.Name = "Day"
dayVar.Value = 0
hourVar = Instance.new("IntValue", game.Lighting)
hourVar.Name = "Hour"
hourVar.Value = 0
minuteVar = Instance.new("IntValue", game.Lighting)
minuteVar.Name = "Minute"
minuteVar.Value = 0
secondVar = Instance.new("IntValue", game.Lighting)
secondVar.Name = "Second"
secondVar.Value = 0
dayOfWeek = Instance.new("StringValue", game.Lighting)
dayOfWeek.Name = "DayOfWeek"
dayOfWeek.Value = "Thursday"
end
function giveZero(data)
if string.len(data) <= 1 then
return "0" .. data
else
return data
end
end
function hasDecimal(value)
if not(value == math.floor(value)) then
return true
else
return false
end
end
function isLeapYear(year)
if(not hasDecimal(year / 4)) then
if(hasDecimal(year / 100)) then
return true
else
if(not hasDecimal(year / 400)) then
return true
else
return false
end
end
else
return false
end
end
local eYear = 1970
local timeStampDayOfWeak = 5
local secondsInHour = 3600
local secondsInDay = 86400
local secondsInYear = 31536000
local secondsInLeapYear = 31622400
local monthWith28 = 2419200
local monthWith29 = 2505600
local monthWith30 = 2592000
local monthWith31 = 2678400
local monthsWith30 = {4, 6, 9, 11}
local monthsWith31 = {1, 3, 5, 7, 8, 10, 12}
local daysSinceEpoch = 0
local DOWAssociates = {"Tursday", "Friday", "Saturday", "Sunday", "Monday", "Tuesday", "Wednesday"}
while(true) do
now = tick()
year = 1970
secs = 0
daysSinceEpoch = 0
while((secs + secondsInLeapYear) < now or (secs + secondsInYear) < now) do
if(isLeapYear(year+1)) then
if((secs + secondsInLeapYear) < now) then
secs = secs + secondsInLeapYear
year = year + 1
daysSinceEpoch = daysSinceEpoch + 366
end
else
if((secs + secondsInYear) < now) then
secs = secs + secondsInYear
year = year + 1
daysSinceEpoch = daysSinceEpoch + 365
end
end
end
secondsRemaining = now - secs
monthSecs = 0
yearIsLeapYear = isLeapYear(year)
month = 1 -- January
while((monthSecs + monthWith28) < secondsRemaining or (monthSecs + monthWith30) < secondsRemaining or (monthSecs + monthWith31) < secondsRemaining) do
if(month == 1) then
if((monthSecs + monthWith31) < secondsRemaining) then
month = 2
monthSecs = monthSecs + monthWith31
daysSinceEpoch = daysSinceEpoch + 31
else
break
end
end
if(month == 2) then
if(not yearIsLeapYear) then
if((monthSecs + monthWith28) < secondsRemaining) then
month = 3
monthSecs = monthSecs + monthWith28
daysSinceEpoch = daysSinceEpoch + 28
else
break
end
else
if((monthSecs + monthWith29) < secondsRemaining) then
month = 3
monthSecs = monthSecs + monthWith29
daysSinceEpoch = daysSinceEpoch + 29
else
break
end
end
end
if(month == 3) then
if((monthSecs + monthWith31) < secondsRemaining) then
month = 4
monthSecs = monthSecs + monthWith31
daysSinceEpoch = daysSinceEpoch + 31
else
break
end
end
if(month == 4) then
if((monthSecs + monthWith30) < secondsRemaining) then
month = 5
monthSecs = monthSecs + monthWith30
daysSinceEpoch = daysSinceEpoch + 30
else
break
end
end
if(month == 5) then
if((monthSecs + monthWith31) < secondsRemaining) then
month = 6
monthSecs = monthSecs + monthWith31
daysSinceEpoch = daysSinceEpoch + 31
else
break
end
end
if(month == 6) then
if((monthSecs + monthWith30) < secondsRemaining) then
month = 7
monthSecs = monthSecs + monthWith30
daysSinceEpoch = daysSinceEpoch + 30
else
break
end
end
if(month == 7) then
if((monthSecs + monthWith31) < secondsRemaining) then
month = 8
monthSecs = monthSecs + monthWith31
daysSinceEpoch = daysSinceEpoch + 31
else
break
end
end
if(month == 8) then
if((monthSecs + monthWith31) < secondsRemaining) then
month = 9
monthSecs = monthSecs + monthWith31
daysSinceEpoch = daysSinceEpoch + 31
else
break
end
end
if(month == 9) then
if((monthSecs + monthWith30) < secondsRemaining) then
month = 10
monthSecs = monthSecs + monthWith30
daysSinceEpoch = daysSinceEpoch + 30
else
break
end
end
if(month == 10) then
if((monthSecs + monthWith31) < secondsRemaining) then
month = 11
monthSecs = monthSecs + monthWith31
daysSinceEpoch = daysSinceEpoch + 31
else
break
end
end
if(month == 11) then
if((monthSecs + monthWith30) < secondsRemaining) then
month = 12
monthSecs = monthSecs + monthWith30
daysSinceEpoch = daysSinceEpoch + 30
else
break
end
end
end
day = 1 -- 1st
daySecs = 0
daySecsRemaining = secondsRemaining - monthSecs
while((daySecs + secondsInDay) < daySecsRemaining) do
day = day + 1
daySecs = daySecs + secondsInDay
daysSinceEpoch = daysSinceEpoch + 1
end
hour = 0 -- Midnight
hourSecs = 0
hourSecsRemaining = daySecsRemaining - daySecs
while((hourSecs + secondsInHour) < hourSecsRemaining) do
hour = hour + 1
hourSecs = hourSecs + secondsInHour
end
minute = 0 -- Midnight
minuteSecs = 0
minuteSecsRemaining = hourSecsRemaining - hourSecs
while((minuteSecs + 60) < minuteSecsRemaining) do
minute = minute + 1
minuteSecs = minuteSecs + 60
end
second = math.floor(now % 60)
year = giveZero(year)
month = giveZero(month)
day = giveZero(day)
hour = giveZero(hour)
minute = giveZero(minute)
second = giveZero(second)
remanderForDOW = daysSinceEpoch % 7
DOW = DOWAssociates[remanderForDOW + 1]
if(createVariable) then
yearVar.Value = year
monthVar.Value = month
dayVar.Value = day
hourVar.Value = hour
minuteVar.Value = minute
secondVar.Value = second
dayOfWeek.Value = DOW
end
if(outputTime) then
str = "Year: " .. year .. ", Month: " .. month .. ", Day: " .. day .. ", Hour: " .. hour .. ", Minute: " .. minute .. ", Second: ".. second .. ", Day of Week: " .. DOW
print(str)
end
wait(1)
end
----ORIGINAL POST----
What are the formulas for calculating the following given no resources except the seconds since Epoch?
Here's a list of what I need:
Current Month of year Ex: 7
Current day of month Ex: 25
Current day of week Ex: Thursday (1-7 would be acceptable)
Current hour of day Ex: 22
Current minute of hour Ex: 34
Current second of minute: 07

Answer 1

Here is some Lua code adapted from some C code found by Google. It does not handle timezones or Daylight Saving Time and so the outputs refers to Universal Coordinated Time (UTC).
-- based on http://www.ethernut.de/api/gmtime_8c_source.html
local floor=math.floor
local DSEC=24*60*60 -- secs in a day
local YSEC=365*DSEC -- secs in a year
local LSEC=YSEC+DSEC -- secs in a leap year
local FSEC=4*YSEC+DSEC -- secs in a 4-year interval
local BASE_DOW=4 -- 1970-01-01 was a Thursday
local BASE_YEAR=1970 -- 1970 is the base year
local _days={
-1, 30, 58, 89, 119, 150, 180, 211, 242, 272, 303, 333, 364
}
local _lpdays={}
for i=1,2 do _lpdays[i]=_days[i] end
for i=3,13 do _lpdays[i]=_days[i]+1 end
function gmtime(t)
print(os.date("!\n%c\t%j",t),t)
local y,j,m,d,w,h,n,s
local mdays=_days
s=t
-- First calculate the number of four-year-interval, so calculation
-- of leap year will be simple. Btw, because 2000 IS a leap year and
-- 2100 is out of range, this formula is so simple.
y=floor(s/FSEC)
s=s-y*FSEC
y=y*4+BASE_YEAR -- 1970, 1974, 1978, ...
if s>=YSEC then
y=y+1 -- 1971, 1975, 1979,...
s=s-YSEC
if s>=YSEC then
y=y+1 -- 1972, 1976, 1980,... (leap years!)
s=s-YSEC
if s>=LSEC then
y=y+1 -- 1971, 1975, 1979,...
s=s-LSEC
else -- leap year
mdays=_lpdays
end
end
end
j=floor(s/DSEC)
s=s-j*DSEC
local m=1
while mdays[m]<j do m=m+1 end
m=m-1
local d=j-mdays[m]
-- Calculate day of week. Sunday is 0
w=(floor(t/DSEC)+BASE_DOW)%7
-- Calculate the time of day from the remaining seconds
h=floor(s/3600)
s=s-h*3600
n=floor(s/60)
s=s-n*60
print("y","j","m","d","w","h","n","s")
print(y,j+1,m,d,w,h,n,s)
end
local t=os.time()
gmtime(t)
t=os.time{year=1970, month=1, day=1, hour=0} gmtime(t)
t=os.time{year=1970, month=1, day=3, hour=0} gmtime(t)
t=os.time{year=1970, month=1, day=2, hour=23-3, min=59, sec=59} gmtime(t)

Answer 2

The formula is not simple for a few reasons, especially leap years. You should probably use the date function on this page rather than trying to calculate it yourself.

Answer 3

You could use luatz
x = 1234567890
t = require "luatz.timetable".new_from_timestamp ( x )
print(t.year,t.month,t.day,t.hour,t.min,t.sec,t.yday,t.wday)
-- Or just
print(t:rfc_3339())

Answer 4

This is how I do it.
> time0=os.time()
> time0
1571439964
> os.date("%Y%m%d%H%M%S",time0)
20191019120604
>

Answer 5

os.date is a standard Lua function, if passing the first argument as "%t", it will return a table containing the following fields: year (four digits), month (1--12), day (1--31), hour (0--23), min (0--59), sec (0--61), wday (weekday, Sunday is 1), yday (day of the year), and isdst (daylight saving flag, a boolean).
Give it a test:
time = os.time()
print("time since epoch: " .. time)
date = os.date("*t", time)
print("year: " .. date.year)
print("month: " .. date.month)
print("day: " .. date.day)
print("hour: " .. date.hour)
print("minute: " .. date.min)
print("second: " .. date.sec)
print("weekday: " .. date.wday)
Output:
time since epoch: 1374826427
year: 2013
month: 7
day: 26
hour: 16
minute: 13
second: 47
weekday: 6

Answer 6

A much faster solution would be to use my method, which I haven't really seen anyone else use because most have access to os.date()
Since I do not have access to os.date(), here is my solution:
local tabIndexOverflow = function(seed, table)
-- This subtracts values from the table from seed until an overflow
-- This can be used for probability :D
for i = 1, #table do
if seed - table[i] <= 0 then
return i, seed
end
seed = seed - table[i]
end
end
local getDate = function(unix)
-- Given unix date, return string date
assert(unix == nil or type(unix) == "number" or unix:find("/Date%((%d+)"), "Please input a valid number to \"getDate\"")
local unix = (type(unix) == "string" and unix:match("/Date%((%d+)") / 1000 or unix or os.time()) -- This is for a certain JSON compatability. It works the same even if you don't need it
local dayCount, year, days, month = function(yr) return (yr % 4 == 0 and (yr % 100 ~= 0 or yr % 400 == 0)) and 366 or 365 end, 1970, math.ceil(unix/86400)
while days >= dayCount(year) do days = days - dayCount(year) year = year + 1 end -- Calculate year and days into that year
month, days = tabIndexOverflow(days, {31,(dayCount(year) == 366 and 29 or 28),31,30,31,30,31,31,30,31,30,31}) -- Subtract from days to find current month and leftover days
-- hours = hours > 12 and hours - 12 or hours == 0 and 12 or hours -- Change to proper am or pm time
-- local period = hours > 12 and "pm" or "am"
-- Formats for you!
-- string.format("%d/%d/%04d", month, days, year)
-- string.format("%02d:%02d:%02d %s", hours, minutes, seconds, period)
return {Month = month, day = days, year = year, hours = math.floor(unix / 3600 % 24), minutes = math.floor(unix / 60 % 60), seconds = math.floor(unix % 60)}
end
You are, however, on your own when it comes to finding the day of the week. I never cared to find whether it be the day of Thor or the day of Frige.