D23Input.hs

module D23 where

import           BasePrelude hiding ((&), lookup, loop)
import           Control.Lens
import qualified Data.Vector as Vector
import           D23Input

type State = (Int, Map Char Int, Vector Op)
env :: Int -> State
env i = (0, Map.empty & at 'a' ?~ i, input)

lookup :: Param -> State -> Int
lookup (R r) st =  st ^. _2 . at r . non 0
lookup (I i) _ = i

interp :: Op -> State -> State
interp (CPY src (R r)) st =
  st & _2 . at r ?~ lookup src st
     & _1 +~ 1
interp (INC (R r)) st =
  st & _2 . at r . _Just +~ 1
     & _1 +~ 1
interp (DEC (R r)) st =
  st & _2 . at r . _Just -~ 1
     & _1 +~ 1
interp (JNZ nonzero away) st =
  st & _1 %~ (\x -> x + (if lookup nonzero st == 0 then 1 else lookup away st))
interp (MULT (R a) (R b) (R c)) st =
  st & _1 +~ 1
     & _2 . at a . _Just .~ lookup (R b) st * lookup (R c) st
interp (TGL (R c)) st =
  st & _1 +~ 1
     & _3 . ix (st ^. _1 + lookup (R c) st) %~ toggle

toggle :: Op -> Op
toggle (CPY a b) = (JNZ a b)
toggle (TGL a) = INC a
toggle (DEC a) = INC a
toggle (INC a) = DEC a
toggle (JNZ a b) = CPY a b

loop st@(i, env, cmds)
  | (Vector.null cmds || i >= length cmds) = st
  | otherwise = loop (interp (cmds ^?! ix i) st)

main =
  print (loop (env 7))
  print (loop (env 12))