advent-of-code-2022/src/Day5/Part1.hs

module Day5.Part1 (
  executeOperation,
  day5_1
) where

import qualified Data.Sequence as S
import Data.Foldable (toList)
import Day5.Shared

executeOperation :: Row -> Operation -> Row
executeOperation row op
  | count op == 1 = updatedRow
  | otherwise = executeOperation updatedRow (Operation { count = count op - 1, from = from op, to = to op })
  where
    originStack = row `S.index` asInt (from op)
    targetStack = row `S.index` asInt (to op)
    movedContent = head $ content originStack
    updatedOrigin = Stack (drop 1 $ content originStack)
    updatedTarget = Stack (movedContent : content targetStack)
    updatedRow = S.update (asInt $ to op) updatedTarget $ S.update (asInt $ from op) updatedOrigin row

day5_1 :: String -> String
day5_1 input = toList . findTopOfStacks $ foldl executeOperation row operations
  where
    (row, operations) = parseInput input