f.hs

longestSuffix :: Domain -> DomTrie -> Maybe Domain
longestSuffix (Domain labels) table =
    (Domain . reverse) <$> go (reverse labels) table Nothing
  where
    go [] _ r = r
    go (x:xs) (DomTrie b table) (Just ts)
      = case M.lookup x table of
        Just sub | b         -> go xs sub (Just (x:ts))
                 | otherwise -> go xs sub (Just ts)
        Nothing  -> Just ts
    go (x:xs) (DomTrie b table) Nothing
      = case M.lookup x table of
        Just sub | b         -> go xs sub (Just [x])
                 | otherwise -> go xs sub Nothing
        Nothing  -> Nothing