Module:Official website

 local makeUrl = require('Module:URL')._url

 local p = {}

 -- Wrapper for pcall which returns nil on failure.
 local function quickPcall(func)
	local success, result = pcall(func)
	if success then
		return result
	end
 end

 -- Gets the rank for a Wikidata property table. Returns 1, 0 or -1, in
 -- order of rank.
 local function getRank(prop)
	local rank = prop.rank
	if rank == 'preferred' then
		return 1
	elseif rank == 'normal' then
		return 0
	elseif rank == 'deprecated' then
		return -1
	else
		-- No rank or undefined rank is treated as "normal".
		return 0
	end
 end

 -- Finds whether a Wikidata property is qualified as being in English.
 local function isEnglish(prop)
	local ret = quickPcall(function ()
		for i, lang in ipairs(prop.qualifiers.P407) do
			if lang.datavalue.value['numeric-id'] == 1860 then
				return true
			end
		end
		return false
	end)
	return ret == true
 end

 -- Fetches the official website URL from Wikidata.
 local fetchWikidataUrl
 fetchWikidataUrl = function()
	-- Get objects for all official sites on Wikidata.
	local websites = quickPcall(function ()
		return mw.wikibase.getAllStatements(mw.wikibase.getEntityIdForCurrentPage(), 'P856')
	end)

	-- Clone the objects in case other code needs them in their original order.
	websites = websites and mw.clone(websites) or {}

	-- Add the table index to the objects in case it is needed in the sort.
	for i, website in ipairs(websites) do
		website._index = i
	end

	-- Sort the websites, first by highest rank, and then by websites in the
	-- English language, then by the website's original position in the
	-- property list. When we are done, get the URL from the highest-sorted
	-- object.
	table.sort(websites, function(ws1, ws2)
		local r1 = getRank(ws1)
		local r2 = getRank(ws2)
		if r1 ~= r2 then
			return r1 > r2
		end
		local e1 = isEnglish(ws1)
		local e2 = isEnglish(ws2)
		if e1 ~= e2 then
			return e1
		end
		return ws1._index < ws2._index
	end)
	local url = quickPcall(function ()
		return websites[1].mainsnak.datavalue.value
	end)

	-- Cache the result so that we only do the heavy lifting once per #invoke.
	fetchWikidataUrl = function ()
		return url
	end

	return url
 end

 -- Render the URL link, plus other visible output.
 local function renderUrl(options)
	if not options.url and not options.wikidataurl then
		local qid = mw.wikibase.getEntityIdForCurrentPage()
		local result = '<strong class="error">' ..
			'No URL found. Please specify a URL here or add one to Wikidata.' ..
			'</strong>'
		if qid then
			result = result.. ' [[File:OOjs UI icon edit-ltr-progressive.svg |frameless |text-top |10px |alt=Edit this at Wikidata |link=https://www.wikidata.org/wiki/' .. qid .. '#P856|Edit this at Wikidata]]'
		end
		return result
	end
	local ret = {}
	ret[#ret + 1] = string.format(
		'<span class="official-website">%s</span>',
		makeUrl(options.url or options.wikidataurl, options.display)
	)
	if options.wikidataurl and not options.url then
		local qid = mw.wikibase.getEntityIdForCurrentPage()
		if qid then
			ret[#ret + 1] = '[[File:OOjs UI icon edit-ltr-progressive.svg |frameless |text-top |10px |alt=Edit this at Wikidata |link=https://www.wikidata.org/wiki/' .. qid .. '#P856|Edit this at Wikidata]]'
		end
	end
	return table.concat(ret, ' ')
 end

 -- Render the tracking category.
 local function renderTrackingCategory(url, wikidataurl)
	if mw.title.getCurrentTitle().namespace ~= 0 then
		return ''
	end
	local category
	if not url and not wikidataurl then
		category = 'Official website missing URL'
	elseif not url and wikidataurl then
		return ''
	elseif url and wikidataurl then
		if url:gsub('/%s*$', '') ~= wikidataurl:gsub('/%s*$', '') then
			category = 'Official website different in Wikidata and Wikipedia'
		end
	else
		category = 'Official website not in Wikidata'
	end
	return category and string.format('[[Category:%s]]', category) or ''
 end

 function p._main(args)
	local url = args[1] or args.URL or args.url
	local wikidataurl = fetchWikidataUrl()
	local formattedUrl = renderUrl{
		url = url,
		wikidataurl = wikidataurl,
		display = args[2] or args.name or 'Official website'
	}
	return formattedUrl .. renderTrackingCategory(url, wikidataurl)
 end

 function p.main(frame)
	local args = require('Module:Arguments').getArgs(frame, {
		wrappers = 'Template:Official website'
	})
	return p._main(args)
 end

 return p