Module:Arguments
-- 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 libraryUtil = require('libraryUtil')
 local checkType = libraryUtil.checkType
 
 local arguments = {}
 
 -- Generate four different tidyVal functions, so that we don't have to check the
 -- options every time we call it.
 
 local function tidyValDefault(key, val)
 	if type(val) == 'string' then
 		val = val:match('^%s*(.-)%s*$')
 		if val == '' then
 			return nil
 		else
 			return val
 		end
 	else
 		return val
 	end
 end
 
 local function tidyValTrimOnly(key, val)
 	if type(val) == 'string' then
 		return val:match('^%s*(.-)%s*$')
 	else
 		return val
 	end
 end
 
 local function tidyValRemoveBlanksOnly(key, val)
 	if type(val) == 'string' then
 		if val:find('%S') then
 			return val
 		else
 			return nil
 		end
 	else
 		return val
 	end
 end
 
 local function tidyValNoChange(key, val)
 	return val
 end
 
 local function matchesTitle(given, title)
 	local tp = type( given )
 	return (tp == 'string' or tp == 'number') and mw.title.new( given ).prefixedText == title
 end
 
 local translate_mt = { __index = function(t, k) return k end }
 
 function arguments.getArgs(frame, options)
 	checkType('getArgs', 1, frame, 'table', true)
 	checkType('getArgs', 2, options, 'table', true)
 	frame = frame or {}
 	options = options or {}
 
 	--[[
 	-- Set up argument translation.
 	--]]
 	options.translate = options.translate or {}
 	if getmetatable(options.translate) == nil then
 		setmetatable(options.translate, translate_mt)
 	end
 	if options.backtranslate == nil then
 		options.backtranslate = {}
 		for k,v in pairs(options.translate) do
 			options.backtranslate[v] = k
 		end
 	end
 	if options.backtranslate and getmetatable(options.backtranslate) == nil then
 		setmetatable(options.backtranslate, {
 			__index = function(t, k)
 				if options.translate[k] ~= k then
 					return nil
 				else
 					return k
 				end
 			end
 		})
 	end
 
 	--[[
 	-- Get the argument tables. If we were passed a valid frame object, get the
 	-- frame arguments (fargs) and the parent frame arguments (pargs), depending
 	-- on the options set and on the parent frame's availability. If we weren't
 	-- passed a valid frame object, we are being called from another Lua module
 	-- or from the debug console, so assume that we were passed a table of args
 	-- directly, and assign it to a new variable (luaArgs).
 	--]]
 	local fargs, pargs, luaArgs
 	if type(frame.args) == 'table' and type(frame.getParent) == 'function' then
 		if options.wrappers then
 			--[[
 			-- The wrappers option makes Module:Arguments look up arguments in
 			-- either the frame argument table or the parent argument table, but
 			-- not both. This means that users can use either the #invoke syntax
 			-- or a wrapper template without the loss of performance associated
 			-- with looking arguments up in both the frame and the parent frame.
 			-- Module:Arguments will look up arguments in the parent frame
 			-- if it finds the parent frame's title in options.wrapper;
 			-- otherwise it will look up arguments in the frame object passed
 			-- to getArgs.
 			--]]
 			local parent = frame:getParent()
 			if not parent then
 				fargs = frame.args
 			else
 				local title = parent:getTitle():gsub('/sandbox$', '')
 				local found = false
 				if matchesTitle(options.wrappers, title) then
 					found = true
 				elseif type(options.wrappers) == 'table' then
 					for _,v in pairs(options.wrappers) do
 						if matchesTitle(v, title) then
 							found = true
 							break
 						end
 					end
 				end
 
 				-- We test for false specifically here so that nil (the default) acts like true.
 				if found or options.frameOnly == false then
 					pargs = parent.args
 				end
 				if not found or options.parentOnly == false then
 					fargs = frame.args
 				end
 			end
 		else
 			-- options.wrapper isn't set, so check the other options.
 			if not options.parentOnly then
 				fargs = frame.args
 			end
 			if not options.frameOnly then
 				local parent = frame:getParent()
 				pargs = parent and parent.args or nil
 			end
 		end
 		if options.parentFirst then
 			fargs, pargs = pargs, fargs
 		end
 	else
 		luaArgs = frame
 	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 = {fargs}
 	argTables[#argTables + 1] = pargs
 	argTables[#argTables + 1] = luaArgs
 
 	--[[
 	-- Generate the tidyVal function. If it has been specified by the user, we
 	-- use that; if not, we choose one of four functions depending on the
 	-- options chosen. This is so that we don't have to call the options table
 	-- every time the function is called.
 	--]]
 	local tidyVal = options.valueFunc
 	if tidyVal then
 		if type(tidyVal) ~= 'function' then
 			error(
 				&quot;bad value assigned to option 'valueFunc'&quot;
 					.. '(function expected, got '
 					.. type(tidyVal)
 					.. ')',
 				2
 			)
 		end
 	elseif options.trim ~= false then
 		if options.removeBlanks ~= false then
 			tidyVal = tidyValDefault
 		else
 			tidyVal = tidyValTrimOnly
 		end
 	else
 		if options.removeBlanks ~= false then
 			tidyVal = tidyValRemoveBlanksOnly
 		else
 			tidyVal = tidyValNoChange
 		end
 	end
 
 	--[[
 	-- Set up the args, metaArgs and nilArgs tables. args will be the one
 	-- accessed from functions, and metaArgs will hold the actual arguments. Nil
 	-- arguments are memoized in nilArgs, and the metatable connects all of them
 	-- together.
 	--]]
 	local args, metaArgs, nilArgs, metatable = {}, {}, {}, {}
 	setmetatable(args, metatable)
 
 	local function mergeArgs(tables)
 		--[[
 		-- Accepts multiple tables as input and merges their keys and values
 		-- into one table. If a value is already present it is not overwritten;
 		-- tables listed earlier have precedence. We are also memoizing nil
 		-- values, which can be overwritten if they are 's' (soft).
 		--]]
 		for _, t in ipairs(tables) do
 			for key, val in pairs(t) do
 				if metaArgs[key] == nil and nilArgs[key] ~= 'h' then
 					local tidiedVal = tidyVal(key, val)
 					if tidiedVal == nil then
 						nilArgs[key] = 's'
 					else
 						metaArgs[key] = tidiedVal
 					end
 				end
 			end
 		end
 	end
 
 	--[[
 	-- Define metatable behaviour. Arguments are memoized in the metaArgs table,
 	-- and are only fetched from the argument tables once. Fetching arguments
 	-- from the argument tables is the most resource-intensive step in this
 	-- module, so we try and avoid it where possible. For this reason, nil
 	-- arguments are also memoized, in the nilArgs table. 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 the argument tables 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)
 		--[[
 		-- Fetches an argument when the args table is indexed. First we check
 		-- to see if the value is memoized, and if not we try and fetch it from
 		-- the argument tables. When we check memoization, we need to check
 		-- metaArgs before nilArgs, as both can be non-nil at the same time.
 		-- If the argument is not present in metaArgs, we also check whether
 		-- pairs has been run yet. If pairs has already been run, we return nil.
 		-- This is because all the arguments will have already been copied into
 		-- metaArgs by the mergeArgs function, meaning that any other arguments
 		-- must be nil.
 		--]]
 		if type(key) == 'string' then
 			key = options.translate[key]
 		end
 		local val = metaArgs[key]
 		if val ~= nil then
 			return val
 		elseif metatable.donePairs or nilArgs[key] then
 			return nil
 		end
 		for _, argTable in ipairs(argTables) do
 			local argTableVal = tidyVal(key, argTable[key])
 			if argTableVal ~= nil then
 				metaArgs[key] = argTableVal
 				return argTableVal
 			end
 		end
 		nilArgs[key] = 'h'
 		return nil
 	end
 
 	metatable.__newindex = function (t, key, val)
 		-- This function is called when a module tries to add a new value to the
 		-- args table, or tries to change an existing value.
 		if type(key) == 'string' then
 			key = options.translate[key]
 		end
 		if options.readOnly then
 			error(
 				'could not write to argument table key &quot;'
 					.. tostring(key)
 					.. '&quot;; the table is read-only',
 				2
 			)
 		elseif options.noOverwrite and args[key] ~= nil then
 			error(
 				'could not write to argument table key &quot;'
 					.. tostring(key)
 					.. '&quot;; overwriting existing arguments is not permitted',
 				2
 			)
 		elseif val == nil then
 			--[[
 			-- If the argument is to be overwritten with nil, we need to erase
 			-- the value in metaArgs, so that __index, __pairs and __ipairs do
 			-- not use a previous existing value, if present; and we also need
 			-- to memoize the nil in nilArgs, so that the value isn't looked
 			-- up in the argument tables if it is accessed again.
 			--]]
 			metaArgs[key] = nil
 			nilArgs[key] = 'h'
 		else
 			metaArgs[key] = val
 		end
 	end
 
 	local function translatenext(invariant)
 		local k, v = next(invariant.t, invariant.k)
 		invariant.k = k
 		if k == nil then
 			return nil
 		elseif type(k) ~= 'string' or not options.backtranslate then
 			return k, v
 		else
 			local backtranslate = options.backtranslate[k]
 			if backtranslate == nil then
 				-- Skip this one. This is a tail call, so this won't cause stack overflow
 				return translatenext(invariant)
 			else
 				return backtranslate, v
 			end
 		end
 	end
 
 	metatable.__pairs = function ()
 		-- Called when pairs is run on the args table.
 		if not metatable.donePairs then
 			mergeArgs(argTables)
 			metatable.donePairs = true
 		end
 		return translatenext, { t = metaArgs }
 	end
 
 	local function inext(t, i)
 		-- This uses our __index metamethod
 		local v = t[i + 1]
 		if v ~= nil then
 			return i + 1, v
 		end
 	end
 
 	metatable.__ipairs = function (t)
 		-- Called when ipairs is run on the args table.
 		return inext, t, 0
 	end
 
 	return args
 end