Module:Pg

require('strict')

local p = {}

-- Return a title using [[Special:MyLanguage]], which resolves to user language
-- at read time if that exists, or English otherwise
local function getMyLanguage(title)
 -- interwiki prefixes for wikis with translate extension
 -- created from https://phabricator.wikimedia.org/source/mediawiki-config/browse/master/wmf-config/InitialiseSettings.php$19151
 -- and https://commons.wikimedia.org/wiki/Special:Interwiki
 -- frwiktionary is excluded because there are multiple wiktionaries
 local multilang = {
  wmam = true,
  wmbe = true,
  betawikiversity = true,
  wmbr = true,
  wmbd = true,
  wmca = true,
  wmge = true,
  wmid = true,
  wmhi = true,
  incubator = true,
  m = true,
  meta = true,
  metawiki = true,
  metawikimedia = true,
  metawikipedia = true,
  wmno = true,
  otrswiki = true,
  vrtwiki = true,
  outreach = true,
  outreachwiki = true,
  wmpl = true,
  wmru = true,
  wmpunjabi = true,
  oldwikisource = true,
  species = true,
  wikispecies = true,
  wmse = true,
  testwiki = true,
  wmua = true,
  d = true,
  wikidata = true,
  wmania = true,
  wikimania = true,
 }
 if title.isExternal then
  if multilang[title.interwiki] then
   -- mw.title.interwiki only seperates the first interwiki or interlanguage
   -- prefix. that means this wouldn't work with a link that has both,
   -- eg 'wikt:fr:foo' -> 'wikt:Special:MyLanguage/fr:foo' which breaks.
   -- if the wiki supports translation, the link probably doesn't have an
   -- interlanguage prefix and Special:MyLanguage might be useful
   return mw.title.new(title.interwiki .. ':Special:MyLanguage/' .. title.nsText .. title.text)
  else
   -- wiki doesn't support translation, so don't try to add Special:MyLanguage
   return title
  end
 else
  return mw.title.new('Special:MyLanguage/' .. title.fullText)
 end
end

-- Get display title for pages translated using the Translate extension
local function getDisplayTitle(title, lang)
 local titlepage = 'Translations:' .. title.prefixedText .. '/Page display title/' .. lang
 local success, display = pcall(function () return mw.getCurrentFrame():expandTemplate{ title = titlepage } end)
 if success then
  if title.fragment ~= '' then
   display = display .. '#' .. title.fragment
  end
  return display
 else
  return nil
 end
end

function p.getLink(page, display, anchor, lang, useMyLanguage)
 -- Sort out things like nil, object etc. It is likely to be invalid title,
 -- but c’est la vie.
 local title = mw.title.new(tostring(page or ''))
 if not title then
  return '[['  .. page .. ']]'
 end
 if anchor then
  title.fragment = anchor
 end
 if title.isRedirect then
  local fragment = title.fragment
  title = title.redirectTarget
  if fragment ~= '' then
   title.fragment = fragment
  end
 end
 if useMyLanguage then
  if not display then
   display = getDisplayTitle(title, lang) or title.fullText
  end
  title = getMyLanguage(title)
 else
  if lang ~= 'en' then
   local subpage = title:subPageTitle(lang)
   if subpage.exists then
    -- version of target page exists in current page language, return that version
    subpage.fragment = title.fragment
    if not display then
     -- try to use translated page title
     display = getDisplayTitle(title, lang)
    end
    title = subpage
   else
    -- prepend Special:MyLanguage/ to return the target page in
    -- user’s preferred language if available
    if not display then
     display = title.fullText
    end
    title = getMyLanguage(title)
   end
  end
 end
 return '[['  .. title.fullText .. (display and '|' .. display or '') .. ']]'
end


function p.main(frame)
 local args = require('Module:Arguments').getArgs(frame, {frameOnly = true})
 local lang = args.lang or mw.getCurrentFrame():preprocess('{{PAGELANGUAGE}}')
 return p.getLink(args.page, args.display, args.anchor, lang, false)
end

function p.pg2(frame)
 local args = require('Module:Arguments').getArgs(frame, {frameOnly = true})
 local lang = args.lang or mw.getCurrentFrame():preprocess('{{int:lang}}')
 return p.getLink(args[1], args[2], args.anchor, lang, true)
end

return p