Exported from Notepad++
-- Simple function to get current date and times
function getdatetime(tz)
local tz = tz or 'America/New_York';
local luatz = require 'luatz';
local function ts2tt(ts)
return luatz.timetable.new_from_timestamp(ts);
end
local utcnow = luatz.time();
local time_zone = luatz.get_tz(tz);
local datetime_raw = tostring(ts2tt(time_zone:localise(utcnow)));
local year, month, day, hour, min, sec, time_reminder = string.match(datetime_raw, "^(%d%d%d%d)%-(%d%d)%-(%d%d)[Tt](%d%d%.?%d*):(%d%d):(%d%d)()");
return year, month, day, hour, min, sec;
end
local current_year, current_month = getdatetime() -- Get current year/Month
local card_expiry_date = 'YYMM'; -- In the app this actually get a value eg: 2204, 2301, 2010, etc.
local card_exp_year = string.sub(card_expiry_date , 3, 4)
local card_exp_month = string.sub(card_expiry_date , 1, 2)
-- Extract the last two digits of the Year
current_year = string.sub(current_year , 3, 4)
-- Check month is valid
if(card_exp_month < '01' or card_exp_month > '12')then
print("This is not a valid month")
else
-- Check date is this month or after
if((card_exp_year < current_year) or (card_exp_year == current_year and card_exp_month < current_month))then
print("Date cannot be before this month.")
else
print("All is good.")
end
end
--
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I do not know if this is the most elegant solution but it works. However it has a huge bug: it will fail at the end of the century. Since I only know the last two digits of the expiry date year, if a card expires in 2102 for instance and we were in 2099 my logic would wrongly reject the date (02 is less than 99).
I am very aware that me an my simple app will likely not be around by then but it bugs me to leave it like this.
Can anyone please suggest a proper way to do this validation?
Thank you!
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Wilmar Pérez 
