module Day7

import Prelude
import Node
import Aoc

Prob : U
Prob = Int × List Int

cases : Int → Int → List Int → Bool
cases goal acc Nil = goal == acc
cases goal acc (x :: xs) =
  if goal < acc then False
  else if cases goal (x + acc) xs then True
  else cases goal (x * acc) xs

part1 : Prob → Bool
part1 (goal, x :: xs) = cases goal x xs
part1 _ = False

cat : Int → Int → Int
cat x y = stringToInt $ show x ++ show y

cases2 : Int → Int → List Int → Bool
cases2 goal acc Nil = goal == acc
cases2 goal acc (x :: xs) =
  if goal < acc then False
  else if cases2 goal (x + acc) xs then True
  else if cases2 goal (x * acc) xs then True
  else cases2 goal (cat acc x) xs

part2 : Prob → Bool
part2 (goal, x :: xs) = cases2 goal x xs
part2 _ = False

parse : String -> Maybe (List Prob)
parse text = do
  traverse parseLine $ split (trim text) "\n"
  where
    parseLine : String → Maybe Prob
    parseLine line = do
      let (a :: b :: Nil) = split line ": " | _ => Nothing
      Just (stringToInt a , nums b)

run : String -> IO Unit
run fn = do
  putStrLn fn
  text <- readFile fn
  let (Just probs) = parse text | _ => putStrLn "parse error"
  let p1 = foldl _+_ 0 $ map fst $ filter part1 probs
  putStrLn $ "part1 " ++ show p1
  let p2 = foldl _+_ 0 $ map fst $ filter part2 probs
  putStrLn $ "part2 " ++ show p2

main : IO Unit
main = do
  run "aoc2024/day7/eg.txt"
  run "aoc2024/day7/input.txt"