Module:Category see also

-- This module implements {{Category see also}}

local mHatnote = require('Module:Hatnote')

local p = {}

local function makeWikitextError(msg)
 return string.format(
  '<strong class="error">Error: %s ([[Template:Category see also]])</strong>',
  msg
 )
end

-- Gets the length of the sequence seq. Usually this should be done with the #
-- operator, but we need to work with tables that get their values through an
-- __index metamethod.
local function getSequenceLength(seq)
 local length = 0
 for i in ipairs(seq) do
  length = i
 end
 return length
end

-- Given a table of options, returns a function that formats categories for
-- those options.
--
-- Options:
-- project - a project code such as "fr" (for the French Wikipedia)
-- showPrefix - a boolean value for whether to show the "Category:" prefix
--              (and the project prefix if specified)
--
-- This is implemented as a function generator rather than a simple function
-- so that we can just process the options once, instead of every time we
-- generate a category.
local function newCategoryLinker(options)
 local formatString
 if options.project then
  if options.showPrefix then
   formatString = '[[:' .. options.project .. ':Category:%s]]'
  else
   formatString = '[[:' .. options.project .. ':Category:%s|%s]]'
  end
 else
  if options.showPrefix then
   formatString = '[[:Category:%s]]'
  else
   formatString = '[[:Category:%s|%s]]'
  end
 end
 return function (category)
  local title = mw.title.new(category)
  local pageName, display
  if not title then
   -- category is not a valid title, usually because of invalid
   -- characters like < or [. Raise an error and suppress the stack
   -- level information so that we can catch it and format the error
   -- message as wikitext.
   error(string.format(
    "'%s' is not a valid category name",
    category
   ), 0)
  elseif title.namespace == 14 then -- Category namespace
   pageName = title.text
   display = title.text
  else
   pageName = title.prefixedText
   display = category
  end
  -- We can get away with using two arguments even when
  -- options.showDisplay is false, as string.format ignores extra
  -- arguments as long as there is an argument for each flag in the
  -- format string.
  return formatString:format(pageName, display)
 end
end

function p._main(args)
 local nLinks = getSequenceLength(args)

 if nLinks < 1 then
  return makeWikitextError('at least one parameter required')
 end

 local makeCategoryLink = newCategoryLinker{
  project = args.project,
  showPrefix = nLinks == 1,
 }

 local links = {}
 for i, cat in ipairs(args) do
  local success, categoryLink = pcall(makeCategoryLink, cat)
  if success then
   links[i] = categoryLink
  else
   -- If there was an error, then categoryLink is the error message.
   return makeWikitextError(categoryLink)
  end
 end

 local formatString
 if nLinks == 1 then
  formatString = '%s: %s'
 else
  formatString = '%s the categories %s'
 end

 -- Don't output a comma before the "and" if we have only two links.
 local conjunction
 if nLinks == 2 then
  conjunction = ' and '
 else
  conjunction = ', and '
 end

 local hatnoteText = formatString:format(
  args.LABEL or 'See also',
  mw.text.listToText(links, ', ', conjunction)
 )
 return mHatnote._hatnote(hatnoteText, {selfref = true})
end

function p.main(frame)
 local args = require('Module:Arguments').getArgs(frame, {
  wrappers = 'Template:Category see also',
 })
 return p._main(args)
end

return p