local p = {}
local getArgs = require('Module:Arguments').getArgs
local yesno = require('Module:Yesno')

function p.makeLink(frame)
	--[[---------
	Variable declaration
	--]]---------
	local args = getArgs(frame)
	local lang = args['explicit_lang_param'] or args['implicit_lang_param'] or 'en'
	local page = mw.title.getCurrentTitle()
	local pagename = page.text
	local wikisourceEdition
	local linkTarget
	local displayText
	local toReturn
	local prefix
	
	--[[
	Create the prefix for the interwiki link
	It uses the lowest of:
	 1. 'Special:Search/', if using the enwiki pagename as the interwiki target
	 2. If not (1), an 'Author:' prefix, localized, if given a works parameter and not under (1)
	 3. If not (1) or (2), the empty string
	We avoid 'Special:Search/Author:' intentionally; this is rarely helpful
	Here we simply set it to (2) or (3), and override it when setting the link target if needed
	--]]
	prefix = args.works and frame:expandTemplate{ title = 'Wikisource/Author', args = { lang } } or ''

	-- Handle multilingual Wikisource (aka old Wikisource) correctly
	if lang == 'mul' then
		wikisourceEdition = 'sourceswiki' -- siteid for multilingual Wikisource
	else
		wikisourceEdition = lang .. 'wikisource' -- other Wikisource editions are langcode + 'wikisource' (e.g. 'enwikisource')
	end
	
	-- get the Wikidata sitelink
	local wikidataSitelink = mw.wikibase.getSitelink(
		mw.wikibase.getEntityIdForCurrentPage() or '',
		wikisourceEdition
	)
		
	-- if we have a language parameter, we look at the second unnamed parameter for the source title
	local checkIndexForTarget = args['implicit_lang_param'] and 2 or 1
	-- and then use the next index for display
	local checkIndexForDisplay = checkIndexForTarget + 1
	
	--[[---------
	Set the link target
	--]]---------
	if args['wslink'] then
		linkTarget = args['wslink']
	elseif args[checkIndexForTarget] then
		-- we have a source title parameter, so return that
		linkTarget = args[checkIndexForTarget]
	elseif wikidataSitelink then
		-- use Wikidata
		linkTarget = wikidataSitelink
	else
		-- we have no parameters and nothing at Wikidata, so we are flying blind
		-- set the linkTarget to the pagename
		linkTarget = pagename
		-- and set prefix to 'Special:Search/' to find the appropriate link
		prefix = 'Special:Search/'
	end
	
	-- clear prefixes for now; will add it back later if needed
	-- this prevents duplicate prefixes (Author:Author:Shakespeare; Special:Search/Special:Search/)
	-- and avoids displayText with any author prefix
	linkTarget = string.gsub(linkTarget, '^' .. prefix, '')
	
	--[[---------	
	Now build the displayText
	--]]---------
	
	if not displayText then
		-- we did not set displayText in the above steps, so set it now
		-- first we check for an explicit display text, or else we set it to be the link target
		displayText = args['title'] or args[checkIndexForDisplay] or linkTarget
	end
	
	--[[---------	
	Now we check whether we should categorize in Category:Wikisource templates with missing id
	--]]---------
	
	-- initialize errorCategory as true
	local errorCategory = true
	
	-- helper to set errorCategory = false
	local function setFalse() errorCategory = false end
	
	if wikidataSitelink then
		-- we do have a sitelink at Wikidata
		setFalse()
	elseif yesno(args.nocat, true) then
		-- we have a |nocat parameter
		setFalse()
	elseif page.namespace ~= 0 then
		-- only care about mainspace
		setFalse()
	elseif string.match(pagename, '^Lists? of ') then
		-- we are on a list page, and those should not have Wikisource links
		setFalse()
	elseif string.match(pagename, '^%d%d?%d?%d?s? in') then
		-- we are in a YEAR/DECADE in FOO page, and those also should not have anything else
		setFalse()
	else
		-- Now we check categories and determine whether this is something which does not need a Wikisource links
		-- Currently, we avoid categorizing:
		-- 1. Disambiguation pages
		-- 2. Set index articles
		-- 3. Articles about species. There is no universal category; [[Category:Articles with 'species' microformats]] is a proxy
		-- we do this check last to avoid using [[WP:EXPENSIVE]] parser calls if possible
		for _, cat in ipairs(page.categories) do
			if cat == "All disambiguation pages" or cat == "All set index articles" or cat == "Articles with 'species' microformats" then
				setFalse()
				break
			end
		end
	end
	
	-- build the link
	toReturn = '[[:s:' .. lang .. ':' .. prefix .. linkTarget .. '|' .. displayText .. ']]'
	
	-- append the error category if needed
	if errorCategory then
		toReturn = toReturn .. '[[Category:Wikisource templates with missing id|' .. pagename .. ']]' 
	end

	return toReturn
end

return p