adventofcode2021_ex2.hs

{-# LANGUAGE FlexibleContexts #-}
import qualified Data.Text    as Text
import qualified Data.Text.Read    as Text
import qualified Data.Text.IO as Text
import qualified Data.Either as Either
import qualified Data.List   as L
import qualified Data.Map.Strict as Map
import Data.Maybe

counter = Map.fromList [("horizontal", 0), ("depth", 0), ("aim", 0)]

getInput = Text.lines <$> Text.readFile "day2.txt"

commands = do
  return . collectCommands . map (\x -> (Text.unpack (x !! 0), fst . head $ Either.rights [(Text.decimal $ x !! 1)])) . map (Text.split (== ' ')) =<< getInput

updateCounter "forward" x c = increaseDepth x (Map.adjust (x +) "horizontal" c)
updateCounter "backward" x c = Map.adjust (\v -> v - x) "horizontal" c
updateCounter "down" x c = Map.adjust (x +) "aim" c
updateCounter "up" x c = Map.adjust (\v -> v - x) "aim" c

collectCommands xs = foldl (\acc comm -> updateCounter (fst comm) (snd comm) acc) counter xs

multiplyFinalValues c = (*) <$> (Map.lookup "depth" c) <*> (Map.lookup "horizontal" c)

increaseDepth x c = Map.adjust (aim +) "depth" c
  where aim = fromJust $ (*) <$> Map.lookup "aim" c <*> Just x


main = do
  comms <- commands
  return $ multiplyFinalValues comms