aoc2021/Day2.hs

{-# LANGUAGE OverloadedStrings #-}

module Day2 where

import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
import Data.Text (splitOn, Text, unpack, pack)


data Submarine = Submarine {
        horizontal :: Int
    ,   depth      :: Int
    }

type Movement = (String, Int)

-- "forward 5" -> ("forward", 5)
parseInstruction :: String -> Movement
parseInstruction instr = (kind, magnitude)
    where
        split = map unpack $ splitOn " " $ pack instr
        kind = head split
        magnitude = read $ split !! 1

move :: Submarine -> Movement -> Submarine
move sub ("forward", magnitude) = sub { horizontal = horizontal sub + magnitude }
move sub ("down", magnitude)    = sub { depth = depth sub + magnitude }
move sub ("up", magnitude)      = sub { depth = depth sub - magnitude }

(++) :: Submarine -> Submarine -> Submarine
x ++ y = Submarine { horizontal = horizontal x + horizontal y, depth = depth x + depth y } 

main :: IO ()
main = do
    input <- openFile "inputs/2.txt" ReadMode 
    contents <- hGetContents input

    let submarine = Submarine { horizontal = 0, depth = 0 }
    let instructions = parseInstruction <$> lines contents
    let sub = foldl move submarine instructions

    print $ horizontal sub * depth sub

    hClose input