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--                               Labelled list                                --

--                                                                            --

-- This module does the core work of creating a hatnote composed of a list    --

-- prefixed by a colon-terminated label, i.e. "LABEL: [andList of pages]",    --

-- for {{see also}} and similar templates.                                    --

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local mHatnote = require('Module:Hatnote')

local mHatlist = require('Module:Hatnote list')

local mArguments --initialize lazily

local yesno --initialize lazily

local p = {}



-- Defaults global to this module

local defaults = {

	label = 'See also', --Final fallback for label argument

	labelForm = '%s: %s',

	prefixes = {'label', 'label ', 'l'},

	template = 'Module:Labelled list hatnote'

}



-- Localizable message strings

local msg = {

	errorSuffix = '#Errors',

	noInputWarning = 'no page names specified',

	noOutputWarning =

		"'''[[%s]] — no output: none of the target pages exist.'''"

}



-- Helper function that pre-combines display parameters into page arguments.

-- Also compresses sparse arrays, as a desirable side-effect.

function p.preprocessDisplays (args, prefixes)

	-- Prefixes specify which parameters, in order, to check for display options

	-- They each have numbers auto-appended, e.g. 'label1', 'label 1', & 'l1'

	prefixes = prefixes or defaults.prefixes

	local indices = {}

	local sparsePages = {}

	for k, v in pairs(args) do

		if type(k) == 'number' then

			indices#indices + 1 = k

			local display

			for i = 1, #prefixes do

				display = argsprefixesi .. k

				if display then break end

			end

			sparsePagesk = display and

				string.format('%s|%s', string.gsub(v, '|.*$', ''), display) or v

		end

	end

	table.sort(indices)

	local pages = {}

	for k, v in ipairs(indices) do pages#pages + 1 = sparsePagesv end

	return pages

end



--Helper function to get a page target from a processed page string

--e.g. "Page|Label" → "Page" or "Target" → "Target"

local function getTarget(pagename)

 	local pipe = string.find(pagename, '|')

	return string.sub(pagename, 0, pipe and pipe - 1 or nil)

end



-- Produces a labelled pages-list hatnote.

-- The main frame (template definition) takes 1 or 2 arguments, for a singular

-- and (optionally) plural label respectively:

-- * {{#invoke:Labelled list hatnote|labelledList|Singular label|Plural label}}

-- The resulting template takes pagename & label parameters normally.

function p.labelledList (frame)

	mArguments = require('Module:Arguments')

	yesno = require('Module:Yesno')

	local labels = {frame.args1 or defaults.label}

	labels2 = frame.args2 or labels1

	labels3 = frame.args3 --no defaulting

	labels4 = frame.args4 --no defaulting

	local template = frame:getParent():getTitle()

	local args = mArguments.getArgs(frame, {parentOnly = true})

	local pages = p.preprocessDisplays(args)

	local options = {

		category = yesno(args.category),

		extraclasses = frame.args.extraclasses,

		ifexists = yesno(frame.args.ifexists),

		labelForm = frame.args.labelForm,

		namespace = frame.args.namespace or args.namespace,

		selfref = yesno(frame.args.selfref or args.selfref),

		template = template

	}

	return p._labelledList(pages, labels, options)

end



function p._labelledList (pages, labels, options)

	if options.ifexists then

		for k = #pages, 1, -1 do --iterate backwards to allow smooth removals

			local v = pagesk

			local title = mw.title.new(getTarget(v), namespace)

			if (v == '') or title == nil or not title.exists then

				table.remove(pages, k)

			end

		end

	end

	labels = labels or {}

	label = (#pages == 1 and labels1 or labels2]) or defaults.label

	for k, v in pairs(pages) do 

		if mHatnote.findNamespaceId(v) ~= 0 then

			label =

				(

					#pages == 1 and

					(labels3 or labels1 or defaults.label) or

					(labels4 or labels2 or defaults.label)

				) or defaults.label

		end

	end

	if #pages == 0 then

		if options.ifexists then

			mw.addWarning(

				string.format(

					msg.noOutputWarning, options.template or defaults.template

				)

			)

			return ''

		else

			return mHatnote.makeWikitextError(

				msg.noInputWarning,

				(options.template or defaults.template) .. msg.errorSuffix,

				options.category

			)

		end

	end

	local text = string.format(

		options.labelForm or defaults.labelForm,

		label,

		mHatlist.andList(pages, true)

	)

	local hnOptions = {

		extraclasses = options.extraclasses,

		selfref = options.selfref

	}

	return mHatnote._hatnote(text, hnOptions)

end



return p