Module:YMD to ISO

local p = {}

local function month_number(month_name) local months_full = {january=1, february=2, march=3, april=4, may=5, june=6, july=7, august=8, september=9, october=10, november=11, december=12} local months_abbr = {jan=1, feb=2, mar=3, apr=4, may=5, jun=6, jul=7, aug=8, sep=9, oct=10, nov=11, dec=12} local month_lc, _ = string.gsub(string.lower(month_name),'%.','',1) local month_num = months_full[month_lc] or months_abbr[month_lc] or 0 if month_lc == 'sept' then month_num = 9 end return month_num end

local function days_in_month(month_num,year) -- modified from code in Module:Citation/CS1/Date_validation local days = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31} 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_length end

local function zero_pad(string) if string.len(string) == 1 then return '0' .. string else return string end end

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) end function 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