Module:Template translation

local this = {}

function this.checkLanguage(subpage, default)

   --[[Check first if there's an apostrophe, because they break the isKnownLanguageTag
       function. This test does not work with regexps, use plain search instead (no need
       to use Unicode parser, apostrophes can only appear isolated as one byte in UTF-8).
       ]]
   if (string.find(subpage, "'", 1, true) == nil)
   then
       -- Return the subpage only if it is a valid language code.
       if (mw.language.isKnownLanguageTag(subpage))
       then
           return subpage
       end
   end
   -- Otherwise there's currently no known language subpage
   return default

end

--[[Get the last subpage of the current page if it is a translation.

   ]]

function this.getLanguageSubpage()

   local subpage = mw.title.getCurrentTitle().subpageText
   return this.checkLanguage(subpage, )

end

--[[Get the last subpage of the current frame if it is a translation.

   Not used locally.
   ]]

function this.getFrameLanguageSubpage(frame)

   local titleparts = mw.text.split(frame:getParent():getTitle(), '/')
   local subpage = titleparts[#titleparts]
   return this.checkLanguage(subpage, )

end

--[[Get the language of the current page.

   Not used locally.
   ]]

function this.getLanguage()

   local subpage = mw.title.getCurrentTitle().subpageText
   return this.checkLanguage(subpage, mw.language.getContentLanguage():getCode())

end

--[[Get the language of the current frame.

   Not used locally.
   ]]

function this.getFrameLanguage(frame)

   local titleparts = mw.text.split(frame:getParent():getTitle(), '/')
   local subpage = titleparts[#titleparts]
   return this.checkLanguage(subpage, mw.language.getContentLanguage():getCode())

end

--[[If on a translation subpage (like Foobar/de), this function renders

   a given template in the same language, if the translation is available.
   Otherwise, the template is rendered in its default language, without
   modification.
   This is aimed at replacing the current implementation of Template:TNT.
   ]]

function this.renderTranslatedTemplate(frame)

   local args = frame.args
   local pagename = args['template']
   
   --[[Check whether the pagename is actually in the Template namespace, or
       if we're transcluding a main-namespace page.
       (added for backward compatibility of Template:TNT)
       ]]
   local title
   local namespace = args['namespace'] or 
   if (namespace ~= ) -- Checks for namespace parameter for custom ns.
   then
       title = mw.title.new(pagename, namespace) -- Costly
   else -- Supposes that set page is in ns10.
       title = mw.title.new(pagename, 'Template') -- Costly
       if (title.id == 0)
       then -- not found in the Template namespace, assume the main namespace (for backward compatibility)
           title = mw.title.new(pagename, ) -- Costly
       end
   end
   
   -- At this point the title should exist, otherwise render a red link to the missing page
   if (title.id == 0)
   then
   	return '' .. title.prefixedText .. ''
   end
   
   -- Get the last subpage and check if it matches a known language code.
   local subpage = this.getLanguageSubpage()
   if (subpage == )
   then
       -- Check if a translation of the pagename exists in English
       local newtitle = mw.title.new(title.prefixedText .. '/' .. 'en') -- Costly
       -- Use the translation when it exists
       if (newtitle.id ~= 0)
       then
           title = newtitle
       end
   else
       -- Check if a translation of the pagename exists in that language
       local newtitle = mw.title.new(title.prefixedText .. '/' .. subpage) -- Costly
       if (newtitle.id == 0)
       then
           -- Check if a translation of the pagename exists in English
           newtitle = mw.title.new(title.prefixedText .. '/' .. 'en') -- Costly
       end
       -- Use the translation when it exists
       if (newtitle.id ~= 0)
       then
           title = newtitle
       end
   end
   
   -- Copy args pseudo-table to a proper table so we can feed it to expandTemplate.
   -- Then render the pagename.
   local arguments = {}
   for k, v in pairs((frame:getParent() or {}).args) do
       -- numbered args >= 1 need to be shifted
   	local n = tonumber(k) or 0
   	if (n > 0)
   	then
   		if (n >= 2)
   		then
               arguments[n - 1] = v
           end
       else
           arguments[k] = v
       end
   end
   return frame:expandTemplate{title = title, args = arguments}

end

return this