Module:Redirect

-- Given a single page name determines what page it redirects to and returns the target page name, or the
-- passed page name when not a redirect. The passed page name can be given as plain text or as a page link.
-- Returns page name as plain text, or when the bracket parameter is given, as a page link. Returns an
-- error message when page does not exist or the redirect target cannot be determined for some reason.

-- Thus these are roughly the same:
-- [[{{#invoke:redirect|main|redirect-page-name}}]] and {{#invoke:redirect|main|redirect-page-name|bracket=yes}}

local p = {}

function p.main(frame)
    -- If called via #invoke, use the args passed into the invoking
    -- template, or the args passed to #invoke if any exist. Otherwise
    -- assume args are being passed directly in from the debug console
    -- or from another Lua module.
    local origArgs
    if frame == mw.getCurrentFrame() then
        origArgs = frame:getParent().args
        for k, v in pairs( frame.args ) do
            origArgs = frame.args
            break
        end
    else
        origArgs = frame
    end
    -- Trim whitespace and remove blank arguments.
    local args = {}
    for k, v in pairs( origArgs ) do
        v = mw.text.trim( v )
        if v ~= '' then
            args[k] = v
        end
    end
    local rname, bracket = args[1], args.bracket
    
    if type(rname) ~= "string" or not mw.ustring.match(rname, "%S") then return end
    bracket = bracket and "[[%s]]" or "%s"
    rname = mw.ustring.match(rname, "%[%[(.+)%]%]") or rname
    
    -- Get the title object, passing the function through pcall 
    -- in case we are over the expensive function count limit.
    local noError, rpage = pcall(mw.title.new, rname)
    if not noError or noError and not rpage or not rpage.isRedirect then
        -- mw.title.new failed, or the page is not a redirect, so use the passed page name.
        return mw.ustring.format(bracket, rname)
    end

    local redirect = mw.ustring.match(rpage:getContent() or "", "^%s*#[Rr][Ee][Dd][Ii][Rr][Ee][Cc][Tt]%s*:?%s*%[%[([^%[%]]-)%]%]" )
    if redirect then
        -- Decode html entities and percent encodings.
        redirect = mw.text.decode(redirect, true)
        redirect = mw.uri.decode(redirect, 'WIKI')
        return mw.ustring.format(bracket, redirect)
    else
        return mw.ustring.format('<span class="error">[[Module:redirect]] error: could not parse redirect - [[%s]]</span>', rname)
    end
end

return p