Module:URL

 --
 -- This module implements {{URL}}
 --
 -- See unit tests at [[Module:URL/tests]]

 local p = {}
 
 function trim(s)
 return (mw.ustring.gsub(s, "^%s*(.-)%s*$", "%1"))
 end

 function safeUri(s)
 local success, uri = pcall(function()
 return mw.uri.new(s)
 end)
 if success then
 return uri
 end
 end

 function p._url(url, text)
 url = trim(url or '')
 text = trim(text or '')
 
 if url == '' then
 if text == '' then
 return mw.getCurrentFrame():expandTemplate{ title = 'tlx', args = { 'URL', "''example.com''", "''optional display text''" } }
 else
 return text
 end
 end
 
 -- If the URL contains any unencoded spaces, encode them, because MediaWiki will otherwise interpret a space as the end of the URL.
 url = mw.ustring.gsub(url, '%s', function(s) return mw.uri.encode(s, 'PATH') end)
 
 -- If there is an empty query string or fragment id, remove it as it will cause mw.uri.new to throw an error
 url = mw.ustring.gsub(url, '#$', '')
 url = mw.ustring.gsub(url, '%?$', '')
 
 -- If it's an HTTP[S] URL without the double slash, fix it.
 url = mw.ustring.gsub(url, '^[Hh][Tt][Tt][Pp]([Ss]?):(/?)([^/])', 'http%1://%3')
 
 local uri = safeUri(url)
 
 -- Handle URL's without a protocol and not protocol-relative, e.g. www.example.com/foo or www.example.com:8080/foo
 if uri and (not uri.protocol or (uri.protocol and not uri.host)) and url:sub(1, 2) ~= '//' then
 url = 'http://' .. url
 uri = safeUri(url)
 end
 
 if text == '' then
 if uri then
 if uri.path == '/' then uri.path = '' end
 
 local port = ''
 if uri.port then port = ':' .. uri.port end
 
 text = mw.ustring.lower(uri.host or '') .. port .. (uri.relativePath or '')
 else -- URL is badly-formed, so just display whatever was passed in
 text = url
 end
 end

 return mw.ustring.format('<span class="url">[%s %s]</span>', url, text)
 end

 function p.url(frame)
 local templateArgs = frame.args
 local url = templateArgs[1] or ''
 local text = templateArgs[2] or ''
 return p._url(url, text)
 end

 return p