Module:Check for deprecated parameters

 -- This module may be used to compare the arguments passed to the parent
 -- with a list of arguments, returning a specified result if an argument is
 -- on the list
 local p = {}

 local function trim(s)
	return s:match('^%s*(.-)%s*$')
 end

 local function isnotempty(s)
	return s and trim(s) ~= ''
 end

 function p.check (frame)
	-- create the table of deprecated values and their matching new value
	local args = frame.args
	local dep_values = {}
	for k, v in pairs(args) do
		if k == 'ignoreblank' or k == 'preview' or k == 'deprecated' then else
			dep_values[k] = v
		end
	end

	-- loop over the parent args and see if any are deprecated
	local values = {}
	local ignoreblank = isnotempty(frame.args['ignoreblank'])
	local pargs = frame:getParent().args
	for k, v in pairs(pargs) do
		if ignoreblank then
			if dep_values[k] and v~='' then
				table.insert(values, k)
			end
		else
			if dep_values[k] then
				table.insert(values, k)
			end	
		end
	end
	
	-- add results to the output tables
	local res = {}
	if #values > 0 then
		local preview = frame.args['preview'] or
			'Page using [['..frame:getParent():getTitle()..']] with deprecated parameter _VALUE_'
		if isnotempty(preview) then
			preview = require('Module:If preview')._warning({
				preview
			})
		end
		-- Kind of dangerous to trust that this is never nil, but I guess it's
		-- preferable to display that the use of the module is broken rather than
		-- have some sort of tracking category for pages which have an unknown
		-- parent tracking template.
		local category = frame.args['category']
		for k, v in pairs(values) do
			local c = category:gsub('_VALUE_', v)
			table.insert(res, c)
			if v == '' then
				-- Fix odd bug for | = which gets stripped to the empty string
				-- and breaks category links
				v = ' '
			end
			local p = preview:gsub(
				'_VALUE_',
				'"'..v..'". Replace with "'..dep_values[v]..'".'
			)
			table.insert(res, p )
		end
	end

	return table.concat(res)
 end

 return p