Module:Sandbox/Mr. Stradivarius/Check ISO 639-1

--[[
-- This module detects whether the first positional parameter is a valid ISO 639-1 language code.
-- If it is, it returns the code. If not, it returns an error and a tracking category. For blank
-- or non-string input, the returns a blank string. The tracking category is sorted by the language
-- code, rather than by the page name.
--]]

local getArgs = require('Module:Arguments').getArgs
local yesno = require('Module:Yesno')

local p = {}

function p.main(frame)
	local args = getArgs(frame)
	return p._main(args)
end

function p._main(args)
	local code = args[1]
	if type(code) ~= 'string' then
		return '' -- code is either not a string or is a blank string that was removed by getArgs.
	end
	local ret = mw.ustring.lower(code)
	if not mw.language.isKnownLanguageTag(ret) then
		ret = '<strong class="error">Error: "' .. code .. '" is not a valid [[List of ISO 639-1 codes|ISO 639-1 code]]</strong>'
		if not yesno(args.nocat) then
			ret = ret .. '[[Category:Pages with invalid ISO 639-1 language codes|' .. code .. ']]'
		end
	end
	return ret
end

return p