EXTENSIONS = {}

string.gsub(
  os.getenv("EXTENSIONS"),
  "[^%s]+",
  function (ext) EXTENSIONS[#EXTENSIONS+1] = ext end
)

function Link(link)
  if link.target:match("^[%w]+://")
  then
    return link
  end

  for _, ext in pairs(EXTENSIONS)
  do
    link.target = link.target:gsub("%."..ext.."$", ".html")
  end

  return link
end