Editing Template translation

local this = {}

function this.checkLanguage(subpage, default)
    --[[Check first if there's an any invalid character that would cause the
        mw.language.isKnownLanguageTag function() to throw an exception:
        - all ASCII controls in [\000-\031\127],
        - double quote ("), sharp sign (#), ampersand (&), apostrophe ('),
        - slash (/), colon (:), semicolon (;), lower than (<), greater than (>),
        - brackets and braces ([, ], {, }), pipe (|), backslash (\\)
        All other characters are accepted, including space and all non-ASCII
        characters (including \192, which is invalid in UTF-8).
    --]]
    if mw.language.isValidCode(subpage) and mw.language.isKnownLanguageTag(subpage)
    --[[However "SupportedLanguages" are too restrictive, as they discard many
        valid BCP47 script variants (only because MediaWiki still does not
        define automatic transliterators for them, e.g. "en-dsrt" or
        "fr-brai" for French transliteration in Braille), and country variants,
        (useful in localized data, even if they are no longer used for
        translations, such as zh-cn, also useful for legacy codes).
        We want to avoid matching subpagenames containing any uppercase letter,
        (even if they are considered valid in BCP 47, in which they are
        case-insensitive; they are not "SupportedLanguages" for MediaWiki, so
        they are not "KnownLanguageTags" for MediaWiki).
        To be more restrictive, we exclude any character
        * that is not ASCII and not a lowercase letter, minus-hyphen, or digit,
          or does not start by a letter or does not finish by a letter or digit;
        * or that has more than 8 characters between hyphens;
        * or that has two hyphens;
        * or with specific uses in template subpages and unusable as languages.
    --]]
    or  string.find(subpage, "^[%l][%-%d%l]*[%d%l]$") ~= nil
    and string.find(subpage, "[%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l]") == nil
    and string.find(subpage, "%-%-") == nil
    and subpage ~= "doc"
    and subpage ~= "layout"
    and subpage ~= "sandbox"
    and subpage ~= "testcases"
    and subpage ~= "init"
    and subpage ~= "preload"
    and subpage ~= "subpage"
    and subpage ~= "subpage2"
    and subpage ~= "sub-subpage"
    and subpage ~= "sub-sub-subpage"
    and subpage ~= "sub-sub-sub-subpage"
    then
        return subpage
    end
    -- Otherwise there's currently no known language subpage
    return default
end

--[[Get the last subpage of an arbitrary page if it is a translation.
    To be used from templates.
    ]]
function this.getLanguageSubpage(frame)
	local title = frame and frame.args[1]
	if not title or title == '' then
		title = mw.title.getCurrentTitle()
	end
	return this._getLanguageSubpage(title)
end

--[[Get the last subpage of an arbitrary page if it is a translation.
    To be used from Lua.
    ]]
function this._getLanguageSubpage(title)
	if type(title) == 'string' then
		title = mw.title.new(title)
	end
	if not title then
		-- invalid title
		return mw.language.getContentLanguage():getCode()
	end
	--[[This code does not work in all namespaces where the Translate tool works.
	--  It works in the main namespace on Meta because it allows subpages there
	--  It would not work in the main namespace of English Wikipedia (but the
	--  articles are monolignual on that wiki).
	--  On Meta-Wiki the main space uses subpages and its pages are translated.
	--  The Translate tool allows translatng pages in all namespaces, even if
	--  the namespace officially does not have subpages.
	--  On Meta-Wiki the Category namespace still does not have subpages enabled,
	--  even if they would be very useful for categorizing templates, that DO have
	--  subpages (for documentatio and tstboxes pages). This is a misconfiguration
	--  bug of Meta-Wiki. The work-around is to split the full title and then
	--  get the last titlepart.
	local subpage = title.subpageText
	--]]
	local titleparts = mw.text.split(title.fullText, '/')
	local subpage = titleparts[#titleparts]
	return this.checkLanguage(subpage, mw.language.getContentLanguage():getCode())
end

--[[Get the last subpage of the current page if it is a translation.
    ]]
function this.getCurrentLanguageSubpage()
	return this._getLanguageSubpage(mw.title.getCurrentTitle())
end

--[[Get the first part of the language code of the subpage, before the '-'.
    ]]
function this.getMainLanguageSubpage()
	parts = mw.text.split( this.getCurrentLanguageSubpage(), '-' )
	return parts[1]
end

--[[Get the last subpage of the current frame if it is a translation.
    Not used locally.
    ]]
function this.getFrameLanguageSubpage(frame)
	return this._getLanguageSubpage(frame:getParent():getTitle())
end

--[[Get the language of the current page.
    Not used locally.
    ]]
function this.getLanguage()
    local subpage = mw.title.getCurrentTitle().subpageText
    return this.checkLanguage(subpage, mw.language.getContentLanguage():getCode())
end

--[[Get the language of the current frame.
    Not used locally.
    ]]
function this.getFrameLanguage(frame)
    local titleparts = mw.text.split(frame:getParent():getTitle(), '/')
    local subpage = titleparts[#titleparts]
    return this.checkLanguage(subpage, mw.language.getContentLanguage():getCode())
end

function this.title(namespace, basepagename, subpage)
    local message, title
    local pagename = basepagename
    if (subpage or '') ~= ''
    then
        pagename = pagename .. '/' .. subpage
    end
    local valid, title = xpcall(function()
            return mw.title.new(pagename, namespace) -- costly
        end, function(msg) -- catch undocumented exception (!?)
            -- thrown when namespace does not exist. The doc still
            -- says it should return a title, even in that case...
            message = msg
        end)
    if valid and title ~= nil and (title.id or 0) ~= 0
    then
        return title
    end
    return { -- "pseudo" mw.title object with id = nil in case of error
        prefixedText = pagename, -- the only property we need below
        message = message -- only for debugging
    }
end

--[[If on a translation subpage (like Foobar/de), this function returns
    a given template in the same language, if the translation is available.
    Otherwise, the template is returned in its default language, without
    modification.
    This is aimed at replacing the current implementation of Template:TNTN.

    This version does not expand the returned template name: this solves the
    problem of self-recursion in TNT when translatable templates need themselves
    to transclude other translable templates (such as Tnavbar).
    ]]
function this.getTranslatedTemplate(frame, withStatus)
    local args = frame.args
    local pagename = args['template']
    
    --[[Check whether the pagename is actually in the Template namespace, or
        if we're transcluding a main-namespace page.
        (added for backward compatibility of Template:TNT)
        ]]
    local title
    local namespace = args['tntns'] or ''
    if (namespace ~= '') -- Checks for tntns parameter for custom ns.
    then
        title = this.title(namespace, pagename) -- Costly
    else -- Supposes that set page is in ns10.
    	namespace = 'Template'
        title = this.title(namespace, pagename) -- Costly
        if title.id == nil
        then -- not found in the Template namespace, assume the main namespace (for backward compatibility)
    	    namespace = ''
            title = this.title(namespace, pagename) -- Costly
        end
    end
    
    -- Get the last subpage and check if it matches a known language code.
    local subpage = args['uselang'] or ''
    if (subpage == '')
    then
        subpage = this.getCurrentLanguageSubpage()
    end
    if (subpage == '')
    then
        -- Check if a translation of the pagename exists in English
        local newtitle = this.title(namespace, pagename, 'en') -- Costly
        -- Use the translation when it exists
        if newtitle.id ~= nil
        then
            title = newtitle
        end
    else
        -- Check if a translation of the pagename exists in that language
        local newtitle = this.title(namespace, pagename, subpage) -- Costly
        if newtitle.id == nil
        then
            -- Check if a translation of the pagename exists in English
            newtitle = this.title(namespace, pagename, 'en') -- Costly
        end
        -- Use the translation when it exists
        if newtitle.id ~= nil
        then
            title = newtitle
        end
    end
    -- At this point the title should exist
    if withStatus then
    	-- status returned to Lua function below
        return title.prefixedText, title.id ~= nil
    else
    	-- returned directly to MediaWiki
        return title.prefixedText
    end
end

--[[If on a translation subpage (like Foobar/de), this function renders
    a given template in the same language, if the translation is available.
    Otherwise, the template is rendered in its default language, without
    modification.
    This is aimed at replacing the current implementation of Template:TNT.
    
    Note that translatable templates cannot transclude themselves other
    translatable templates, as it will recurse on TNT. Use TNTN instead
    to return only the effective template name to expand externally, with
    template parameters also provided externally.
    ]]
function this.renderTranslatedTemplate(frame)
	local title, found = this.getTranslatedTemplate(frame, true)
    -- At this point the title should exist prior to performing the expansion
    -- of the template, otherwise render a red link to the missing page
    -- (resolved in its assumed namespace). If we don't tet this here, a
    -- script error would be thrown. Returning a red link is consistant with
    -- MediaWiki behavior when attempting to transclude inexistant templates.
	if not found then
		return '[[' .. title .. ']]'
	end

    -- Copy args pseudo-table to a proper table so we can feed it to expandTemplate.
    -- Then render the pagename.
    local args = frame.args
    local pargs = (frame:getParent() or {}).args
    local arguments = {}
    if (args['noshift'] or '') == ''
    then
        for k, v in pairs(pargs) do
            -- numbered args >= 1 need to be shifted
            local n = tonumber(k) or 0
            if (n > 0)
            then
                if (n >= 2)
                then
                    arguments[n - 1] = v
                end
            else
                arguments[k] = v
            end
        end
    else -- special case where TNT is used as autotranslate
    	-- (don't shift again what is shifted in the invokation)
        for k, v in pairs(pargs) do
            arguments[k] = v
        end
    end
    arguments['template'] = title -- override the existing parameter of the base template name supplied with the full name of the actual template expanded
    arguments['tntns'] = nil -- discard the specified namespace override
    arguments['uselang'] = args['uselang'] -- argument forwarded into parent frame
    arguments['noshift'] = args['noshift'] -- argument forwarded into parent frame
    
    return frame:expandTemplate{title = ':' .. title, args = arguments}
end

--[[A helper for mocking TNT in Special:TemplateSandbox. TNT breaks
    TemplateSandbox; mocking it with this method means templates won't be
    localized but at least TemplateSandbox substitutions will work properly.
    Won't work with complex uses.
    ]]
function this.mockTNT(frame)
    local pargs = (frame:getParent() or {}).args
    local arguments = {}
    for k, v in pairs(pargs) do
        -- numbered args >= 1 need to be shifted
        local n = tonumber(k) or 0
        if (n > 0)
        then
            if (n >= 2)
            then
                arguments[n - 1] = v
            end
        else
            arguments[k] = v
        end
    end
    if not pargs[1]
    then
    	return ''
	end
    return frame:expandTemplate{title = 'Template:' .. pargs[1], args = arguments}
end

return this