Difference between revisions of "Module:Arguments"

Revision as of 04:03, 9 December 2013

-- This module provides easy processing of arguments passed to Scribunto from #invoke.
-- It is intended for use by other Lua modules, and should not be called from #invoke directly.

local arguments = {}

function arguments.getArgs(frame, options)
	options = type(options) == 'table' and options or {}

	-- Get the arguments from the frame object if available. If the frame object is not available, we are being called
	-- from another Lua module or from the debug console, so put the args in a special table so we can differentiate them.
	local fargs, pargs, luaArgs
	if frame == mw.getCurrentFrame() then
		fargs = frame.args
		pargs = frame:getParent().args
	else
		luaArgs = type(frame) == 'table' and frame or {}
	end

	-- Set up the args and metaArgs tables. args will be the one accessed from functions, and metaArgs will hold the actual arguments.
	-- The metatable connects the two together.
	local args, metaArgs, metatable = {}, {}, {}
	setmetatable(args, metatable)

	local function tidyVal(key, val)
		-- Processes a value according to the options given to getArguments. Can trim whitespace and remove blanks.
		-- Keys are not used here, but they can be used by user-generated functions, so defining it here to avoid breakage.
		if type(val) == 'string' then
			if options.trim ~= false then
				val = mw.text.trim(val)
			end
			if options.removeBlanks == false or mw.ustring.find(val, '%S') then
				return val
			end
		else
			return val
		end
	end

	-- Use a user-generated function to tidy the values if specified.
	local valueFunc = options.valueFunc
	if valueFunc then
		local valueFuncType = type(valueFunc)
		if valueFuncType == 'function' then
			tidyVal = valueFunc
		else
			error('type error in option "valueFunc": expected function, got ' .. valueFuncType, 2)
		end
	end

	local function mergeArgs(iterator, tables)
		-- Accepts multiple tables as input and merges their keys and values into one table using the specified iterator.
		-- If a value is already present it is not overwritten; tables listed earlier have precendence.
		for _, t in ipairs(tables) do
			for key, val in iterator(t) do
				if metaArgs[key] == nil then
					metaArgs[key] = tidyVal(key, val)
				end
			end
		end
	end

	-- Set the order of precedence of the argument tables. If the variables are nil, nothing will be added to the table,
	-- which is how we avoid clashes between the frame/parent args and the Lua args.
	local argTables = {}
	if options.parentFirst then
		table.insert(argTables, pargs)
		table.insert(argTables, fargs)
	else
		table.insert(argTables, fargs)
		table.insert(argTables, pargs)
	end
	table.insert(argTables, luaArgs)

	--[[
	-- Define metatable behaviour. Arguments are stored in the metaArgs table, and are only fetched from the
	-- argument tables once. Also, we keep a record in the metatable of when pairs and ipairs have been called,
	-- so we do not run pairs and ipairs on fargs and pargs more than once. We also do not run ipairs on fargs
	-- and pargs if pairs has already been run, as all the arguments will already have been copied over.
	--]]
	metatable.__index = function (t, key)
		local val = metaArgs[key]
		if val ~= nil then
			return val
		else
			for i, argTable in ipairs(argTables) do
				local argTableVal = tidyVal(argTable[key])
				if argTableVal ~= nil then
					metaArgs[key] = argTableVal
					return argTableVal
				end
			end
		end
	end

	metatable.__newindex = function (t, key, val)
		if not options.readOnly and (not options.noOverwrite or args[key] == nil) then
			metaArgs[key] = val
		end
	end

	metatable.__pairs = function ()
		if not metatable.donePairs then
			mergeArgs(pairs, argTables)
			metatable.donePairs = true
			metatable.doneIpairs = true
		end
		return pairs(metaArgs)
	end

	metatable.__ipairs = function ()
		if not metatable.doneIpairs then
			mergeArgs(ipairs, argTables)
			metatable.doneIpairs = true
		end
		return ipairs(metaArgs)
	end
	
	return args
end

return arguments