Module:Arguments

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    Documentation for this module may be created at Module:Arguments/doc

    -- 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(
    				"bad value assigned to option 'valueFunc'"
    					.. '(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 "'
    					.. tostring(key)
    					.. '"; the table is read-only',
    				2
    			)
    		elseif options.noOverwrite and args[key] ~= nil then
    			error(
    				'could not write to argument table key "'
    					.. tostring(key)
    					.. '"; 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
    
    return arguments