Module:Detect singular

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Lua to determine whether a string is singular or plural. Designed for use in infoboxes, to determine whether labels should be singular or plural based on the corresponding data, e.g.

{{#invoke:Detect singular|pluralize|Wynken, Blynken, and Nod||singular|plural}} → plural

• See Template:Detect singular for main() usage. Test cases here.
• See Template:Pluralize from text for pluralize() usage (a wrapper around main()). Test cases here.

The above documentation is transcluded from Module:Detect singular/doc. (edit | history)
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local p = {}
local getArgs = require('Module:Arguments').getArgs
local yesNo = require('Module:Yesno')

local function plainFind(s, sub)
	return mw.ustring.find(s, sub, 1, true)
end

local function countMatches(s, pattern)
	local _, count = mw.ustring.gsub(s, pattern, '')
	return count
end

function p._main(origArgs)
	local args = {}
	-- canonicalize boolean arguments
	for key, default in pairs({no_comma=false,bullets=true,ignore_links=true}) do
		if origArgs[key] == nil then
			args[key] = default
		else
			args[key] = yesNo(origArgs[key],default)
		end
	end
	local checkComma = not args.no_comma
	local checkBullets = args.bullets
	local rewriteLinks = args.ignore_links
	local s = origArgs[1]  -- the input string
	if not s then
		return nil -- empty input returns nil
	end
	s = tostring(s)
	if plainFind(s,'forcedetectsingular') then -- magic data string to return true
		return true
	end
	if plainFind(s,'forcedetectplural') then -- magic data string to return false
		return false
	end
	-- count number of list items
	local numListItems = countMatches(s,'<%s*li')
	-- if exactly one, then singular, if more than one, then plural
	if numListItems == 1 then
		return true
	end
	if numListItems > 1 then
		return false
	end
	-- replace all wikilinks with fixed string
	if rewriteLinks then
		s = mw.ustring.gsub(s,'%b[]','WIKILINK') 
	end
	local hasComma = checkComma and mw.ustring.find(s, '%D,%D') 
	local hasAnd = mw.ustring.find(s,'[,%s]and%s')
	local hasBreak = mw.ustring.find(s,'<%s*br')
	local hasBullets = checkBullets and countMatches(s,'%*+') > 1
	local multipleQids = mw.ustring.find(s,'Q%d+[%p%s]+Q%d+') -- has multiple QIDs in a row
	return not (hasComma or hasAnd or hasBreak or hasBullets or multipleQids)
end

function p._pluralize(args)
	local singularForm = args[3] or ""
	local pluralForm = args[4] or ""
	if args[5] then
		singularForm = '[['..args[5]..'|'..singularForm..']]'
		pluralForm = '[['..args[5]..'|'..pluralForm..']]'
	end
	return args[2] and pluralForm or p._main(args) and singularForm or pluralForm
end

function p.main(frame)
	local args = getArgs(frame)
	if p._main(args) then
		return 1
	end
	return ""
end

function p.pluralize(frame)
	local args = getArgs(frame)
	return p._pluralize(args)
end

return p