{-# LANGUAGE LambdaCase #-}
module Main where

import Data.List as L
import Data.Maybe
import Safe

data InputOptions = Elf1
                  | Elf3
                  | Quit


getInput :: IO InputOptions
getInput = do
  putStrLn "Only get top Elf or sum of top 3 Elf? (1/3/q)"
  getLine >>= \case
       "1" -> return Elf1
       "3" -> return Elf3
       "q" -> return Quit
       _   -> putStrLn "not understood" >> getInput
main :: IO ()
main = getInput >>= \case
    Quit -> putStrLn "bye!"
    Elf1 -> interact $
          (<>"\n")
        . show
        . maximum
        . fmap (sum . mapMaybe (readMay :: String -> Maybe Integer))
        . splitOn ""
        . lines
    Elf3 -> interact $
          (<>"\n")
        . show
        . sum
        . take 3
        . sortOn negate
        . fmap (sum . mapMaybe (readMay :: String -> Maybe Integer))
        . splitOn ""
        . lines


-- | Split a list into sublists delimited by the given element.
--
-- From: https://hackage.haskell.org/package/haskell-gi-0.26.2/docs/src/Data.GI.CodeGen.Util.html#splitOn
splitOn :: Eq a => a -> [a] -> [[a]]
splitOn x xs = go xs []
    where go [] acc = [reverse acc]
          go (y : ys) acc = if x == y
                            then reverse acc : go ys []
                            else go ys (y : acc)