module Day10 where

import Data.Maybe
import Data.List (sort)
import Control.Monad (foldM)

closing :: Char -> Maybe Char
closing '(' = Just ')'
closing '[' = Just ']'
closing '{' = Just '}'
closing '<' = Just '>'
closing _ = Nothing

score :: Char -> Maybe Int
score ')' = Just 3
score ']' = Just 57
score '}' = Just 1197
score '>' = Just 25137
score _ = Nothing

closingScore :: Char -> Int
closingScore ')' = 1
closingScore ']' = 2
closingScore '}' = 3
closingScore '>' = 4

calcScore :: String -> Int
calcScore xs = foldr (\char score -> score*5 + closingScore char) 0 (reverse xs)


getInvalidChar :: [Char] -> String -> Char
getInvalidChar _ [] = ' '
getInvalidChar st (x:xs)
    | x `elem` "([{<" = getInvalidChar (x:st) xs
    | otherwise = if Just x == (listToMaybe st >>= closing) then getInvalidChar (tail st) xs else x

getCompletionString :: [Char] -> String -> String
getCompletionString st [] = map (fromJust . closing) st
getCompletionString st (x:xs)
    | x `elem` "([{<" = getCompletionString (x:st) xs
    | otherwise = if Just x == (listToMaybe st >>= closing) then getCompletionString (tail st) xs else ""


main :: IO ()
main = do
    input <- lines <$> getContents

    putStr "part 1: "
    let chars = mapMaybe (score . getInvalidChar []) input
    print $ sum chars

    putStr "part 2: "
    let compls = filter (> 0) $ map (calcScore . getCompletionString []) input
    print $ sort compls !! (length compls `div` 2)