Module:YYMMDDSentence1

local p = {}

function p.generate(frame)

   local dateStr = frame.args[1] or mw.title.getCurrentTitle().text
   
   -- Determine if it's YYMMDD (6 digits) or YYYYMMDD (8 digits)
   local yyyy, mm, dd
   
   if #dateStr == 8 then
       -- YYYYMMDD format
       yyyy = tonumber(dateStr:sub(1, 4))
       mm = tonumber(dateStr:sub(5, 6))
       dd = tonumber(dateStr:sub(7, 8))
   elseif #dateStr == 6 then
       -- YYMMDD format
       local yy = tonumber(dateStr:sub(1, 2))
       mm = tonumber(dateStr:sub(3, 4))
       dd = tonumber(dateStr:sub(5, 6))
       yyyy = 2000 + yy
   else
       return "Error: Invalid date format. Expected YYMMDD or YYYYMMDD."
   end
   
   -- Validate input
   if not yyyy or not mm or not dd then
       return "Error: Invalid date format."
   end
   
   if mm < 1 or mm > 12 then
       return "Error: Invalid month."
   end
   
   if dd < 1 or dd > 31 then
       return "Error: Invalid day."
   end
   
   -- Month names
   local monthNames = {
       "January", "February", "March", "April", "May", "June",
       "July", "August", "September", "October", "November", "December"
   }
   
   -- Day of week names
   local dayNames = {
       "Sunday", "Monday", "Tuesday", "Wednesday",
       "Thursday", "Friday", "Saturday"
   }
   
   -- Ordinal names
   local ordinals = {
       "first", "second", "third", "fourth", "fifth"
   }
   
   -- Calculate day of week using os.date
   local success, timestamp = pcall(os.time, {year = yyyy, month = mm, day = dd, hour = 12})
   if not success then
       return "Error: Invalid date."
   end
   
   local weekday = tonumber(os.date("%w", timestamp)) + 1  -- 1-7, Sunday=1
   
   -- Calculate which occurrence of this weekday in the month
   local occurrence = math.ceil(dd / 7)
   
   -- Get month name
   local monthName = monthNames[mm]
   local dayName = dayNames[weekday]
   local ordinal = ordinals[occurrence]
   
   -- Format day with leading zero
   local dayFormatted = string.format("%02d", dd)
   
   -- Build the sentence (no punctuation at the end)
   local sentence = string.format(
       "%s %s %d was the %s %s of the month",
       monthName, dayFormatted, yyyy, ordinal, dayName
   )
   
   return sentence

end

return p