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(
    "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