date string to unixtime in redis with lua

unixtime.lua

local function YearInSec(y)
  -- returns seconds of a year
  if ((y % 400) == 0) or (((y % 4) == 0) and ((y % 100) ~= 0)) then
    return 31622400 -- 366 * 24 * 60 * 60
  else
    return 31536000 -- 365 * 24 * 60 * 60
  end
end

local function IsLeapYear(y)
  -- returns true of false
  return ((y % 400) == 0) or (((y % 4) == 0) and ((y % 100) ~= 0))
end

local function unixtime(date)
  -- date = "2013-01-13 15:45:13"
  local days = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
  local daysec = 86400
  local y,m,d,h,mi,s = date:match("(%d+)-(%d+)-(%d+)%s+(%d+):(%d+):(%d+)") 
  local time = 0
  
  -- sum years
  for n = 1970,(y - 1) do 
    time = time + YearInSec(n)
  end
  
  -- sum month
  for n = 1,(m - 1) do
    time = time + (days[n] * daysec)
  end
  
  -- add days
  time = time + (d - 1) * daysec
  
  -- if current year is leap year and february is in the past  
  -- it seems that m + 0 is much faster than tonumber(m) 
  -- this currently works with 5.1, 5.2 and 5.3 but in future lua versions this can be removed
  if IsLeapYear(y) and (m + 0 > 2) then
    time = time + daysec
  end
  
  -- add hour, minute and seconds
  return time + (h * 3600) + (mi * 60) + s 
    
end


local S = unixtime(ARGV[1]) -- this is the score, currently in date string form

return redis.call("ZADD", KEYS[1], S, ARGV[2])

How to format the unixtime into "2013-01-13 15:45:13"?

Just reverse the calculation :)

1. determine seconds (line 44)
2. determine minute (line 44)
3. determine hour (also line 44)
4. determine day (line 34)
5. determine month (line 29-30)
6. determine year (line 24-25)
7. build date string (line 20)