Module:British regnal year

-- This module implements N/A. It converts a year in the Gregorian -- calendar to the equivalent English or British regnal year.

local data = mw.loadData( 'Module:British regnal year/data' )

local p = {}

function p.main( frame )

   -- If we are being called from #invoke, then the year is the first positional
   -- argument. If not, it is the frame parameter.
   local inputYear
   if frame == mw.getCurrentFrame() then
       inputYear = frame:getParent().args[ 1 ]
       local frameArgsYear = frame.args[ 1 ]
       if frameArgsYear then
           inputYear = frameArgsYear
       end
   else
       inputYear = frame
   end

   -- Convert the input to an integer if possible. Return "N/A" if the input could
   -- not be converted, or if the converted input is too big or too small.
   if type( inputYear ) ~= 'number' then
       inputYear = tonumber( inputYear )
   end
   if not inputYear then
       return "N/A"
   end
   local currentYear = tonumber( mw.language.getContentLanguage():formatDate( 'Y' ) )
   if inputYear < 1066 or inputYear > currentYear then
       return "N/A"
   end
   
   -- Find the year in the data page and display the output.
   for _, t in ipairs( data ) do
       local dataYear = t.year
       if inputYear >= dataYear then
           -- Get data values from the data page.
           local startYear = t.startYear
           local currentRegnalYear = inputYear - dataYear + startYear
           local linkCurrent = t.linkCurrent
           local prevEndYear = t.prevEndYear
           local linkPrev = t.linkPrev
           local note = t.note

           if inputYear > dataYear then
               -- Years with the same monarch.
               return mw.ustring.format(
                   '%d %s – %d %s%s',
                   currentRegnalYear - 1, linkCurrent, currentRegnalYear, linkCurrent, note or 
               )
           elseif inputYear == dataYear and prevEndYear and linkPrev then
               -- Years with a different monarch.
               return mw.ustring.format(
                   '%d %s – %d %s%s',
                   prevEndYear, linkPrev, currentRegnalYear, linkCurrent, note or 
               )
           else
               -- This should only match the year 1066.
               return mw.ustring.format(
                   '%d %s%s',
                   currentRegnalYear, linkCurrent, note or 
               )
           end
       end
   end

end

return p