Module:Arguments

    From Nonbinary Wiki
    Revision as of 05:40, 13 January 2014 by m>Mr. Stradivarius (tweak one of the comments and make some beautification fixes, now that this is in the job queue)

    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 = {}
    
    local nilArg = {} -- Used for memoizing nil arguments in metaArgs.
    
    -- 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
    
    function arguments.getArgs(frame, options)
    	checkType('getArgs', 1, frame, 'table', true)
    	checkType('getArgs', 2, options, 'table', true)
    	frame = frame or {}
    	options = 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 assign the args to a new variable so we can differentiate them.
    	local fargs, pargs, luaArgs
    	if type(frame.args) == 'table' and type(frame.getParent) == 'function' then
    		if not options.parentOnly then
    			fargs = frame.args
    		end
    		if not options.frameOnly then
    			pargs = frame:getParent().args
    		end
    		if options.parentFirst then
    			fargs, pargs = pargs, fargs
    		end
    	else
    		luaArgs = frame
    	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)
    
    	-- 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
    
    	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 precedence.
    		-- We are also memoizing nil values, but those values can be overwritten.
    		for _, t in ipairs(tables) do
    			for key, val in iterator(t) do
    				local metaArgsVal = metaArgs[key]
    				if metaArgsVal == nil or metaArgsVal == nilArg then
    					local tidiedVal = tidyVal(key, val)
    					if tidiedVal == nil then
    						metaArgs[key] = nilArg
    					else
    						metaArgs[key] = tidiedVal
    					end
    				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 = {fargs}
    	argTables[#argTables + 1] = pargs
    	argTables[#argTables + 1] = luaArgs
    
    	--[[
    	-- Define metatable behaviour. Arguments are memoized in the metaArgs table, and are only fetched from the
    	-- argument tables once. Nil arguments are also memoized using the nilArg variable in order to increase
    	-- performance. 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
    			if val == nilArg then
    				return nil
    			else
    				return val
    			end
    		end
    		for _, argTable in ipairs(argTables) do
    			local argTableVal = tidyVal(key, argTable[key])
    			if argTableVal == nil then
    				metaArgs[key] = nilArg
    			else
    				metaArgs[key] = argTableVal
    				return argTableVal
    			end
    		end
    		return nil
    	end
    
    	metatable.__newindex = function (t, key, val)
    		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
    			metaArgs[key] = nilArg -- Memoize nils.
    		else
    			metaArgs[key] = val
    		end
    	end
    
    	metatable.__pairs = function ()
    		if not metatable.donePairs then
    			mergeArgs(pairs, argTables)
    			metatable.donePairs = true
    			metatable.doneIpairs = true
    		end
    		return function (t, k)
    			local nk, val = next(metaArgs, k)
    			if val == nilArg then
    				val = nil
    			end
    			return nk, val
    		end
    	end
    
    	metatable.__ipairs = function ()
    		if not metatable.doneIpairs then
    			mergeArgs(ipairs, argTables)
    			metatable.doneIpairs = true
    		end
    		return function (t, i)
    			local val = metaArgs[i + 1]
    			if val == nil then
    				return nil
    			elseif val == nilArg then
    				val = nil
    			end
    			return i + 1, val
    		end, nil, 0
    	end
    
    	return args
    end
    
    return arguments