module Stream (
    Stream(..)
  ) where

import Data.List (intercalate)

data Stream a = Stream [(a, Stream a)] deriving Show

instance Semigroup (Stream a) where
  (<>) (Stream []) b = b
  (<>) (Stream pairs) b = Stream $ (\(a, stream) -> (a, stream <> b)) <$> pairs

instance Monoid (Stream a) where
  mempty = fromList []

fromList :: [a] -> Stream a
fromList [] = Stream []
fromList (pair:pairs) = Stream [(pair, fromList pairs)]

infinite :: a -> Stream a
infinite a = Stream [(a, infinite a)]

showTree :: Show a => Stream a -> String
showTree = intercalate "\n" . getLines
  where
    getLines (Stream []) = ["●"]
    getLines (Stream pairs) =
      concat $ (\(a, stream) -> showElem a $ getLines stream) <$> pairs

showElem :: Show a => a -> [String] -> [String]
showElem _ [] = []
showElem a [l] = ["— " ++ show a ++ " —" ++ l]
showElem a (l:ls) =
  let prefix = "─ " ++ show a ++ " ─┬" in
  let padding = take (length prefix - 1) $ repeat ' ' in
  (prefix ++ l) : (pad padding ls)
  where
    pad _ [] = []
    pad padding [x] = [padding ++ '╰' : x]
    pad padding (x:xs) = (padding ++ '├' : x) : (pad padding xs)