Module:YMD to ISO explained

local p =

local function month_number(month_name) local months_full = local months_abbr = local month_lc, _ = string.gsub(string.lower(month_name),'%.',,1) local month_num = months_full[month_lc] or months_abbr[month_lc] or 0 return month_numend

local function days_in_month(month_num,year) -- modified from code in Module:Citation/CS1/Date_validation local days = local month_length if month_num

2 then -- February: 28 days, unless leap year month_length = 28 if year <= 1582 then -- Julian calendar before Oct 1582 if (year%4)

0 then month_length = 29 -- if leap year, then 29 days end else -- Gregorian calendar since Oct 1582 if ((year%4)

0 and ((year%100)~=0 or (year%400)

0)) then month_length = 29 -- if leap year, then 29 days end end else -- not February, get number of days for month month_length = days[month_num] end return month_lengthend

local function zero_pad(string) if string.len(string)

1 then return '0' .. string else return string endend

function p.main(frame) if frame.args[1]

nil then return -- first argument is missing end local arg1, _ = string.gsub(mw.text.trim(frame.args[1]),'_',' ') return p._main(arg1)endfunction p._main(arg1) if arg1

then return -- first argument is empty end if not arg1:match('^%d%d%d%d %a%a%a%a?%.?%a?%a?%a?%a?%a?%a? *%d%d?$') then return arg1 -- invalid date pattern end local year, month_name, day = string.match(arg1, '^(%d%d%d%d) *(%a%a%a%a?%.?%a?%a?%a?%a?%a?%a?) *(%d%d?)$') if month_number(month_name)

0 then return arg1 -- invalid month name or abbreviation end if tonumber(day) < 1 or tonumber(day) > days_in_month(month_number(month_name),tonumber(year)) then return arg1 -- invalid day number for given month end return year .. '-' .. zero_pad(tostring(month_number(month_name))) .. '-' .. zero_pad(day)end

return p