# 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(, options)  
checkType('getArgs', 1, , 'table', true)  
checkType('getArgs', 2, options, 'table', true)  
= 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 object, get the  
-- arguments (fargs) and the parent arguments (pargs), depending  
-- on the options set and on the parent 's availability. If we weren't  
-- passed a valid 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(.args) == 'table' and type(.getParent) == 'function' then  
if options.wrappers then  
---
-- The wrappers option makes Module:Arguments look up arguments in  
-- either the 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 and the parent .  
-- Module:Arguments will look up arguments in the parent  
-- if it finds the parent 's title in options.wrapper;  
-- otherwise it will look up arguments in the object passed  
-- to getArgs.  
---
local parent = :getParent  
if not parent then  
fargs = .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 = .args  
end  
end  
else  
-- options.wrapper isn't set, so check the other options.  
if not options.parentOnly then  
fargs = .args  
end  
if not options.frameOnly then  
local parent = :getParent  
pargs = parent and parent.args or nil  
end  
end  
if options.parentFirst then  
fargs, pargs = pargs, fargs  
end  
else  
luaArgs =  
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 /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