module Day1

import Prelude
import Node

parseLine : String → Maybe Int
parseLine s = case unpack s of
  ('L' :: rest) => Just $ 0 - stringToInt (pack rest)
  ('R' :: rest) => Just $ stringToInt (pack rest)
  _ => Nothing

parse : String → List Int
parse text = mapMaybe parseLine $ split (trim text) "\n"

part1 : List Int → Int
part1 xs = go 0 50 xs
  where
    go : Int → Int → List Int → Int
    go acc pos Nil = acc
    go acc pos (x :: xs) =
      let pos = mod (x + pos)  100
          acc = if pos == 0 then acc + 1 else acc
      in go acc pos xs

-- This is uglier than I'd like
part2 : List Int → Nat
part2 xs = go Z 50 xs
  where
    go : Nat → Int → List Int → Nat
    go acc pos Nil = acc
    go acc pos (0 :: xs) = go acc pos xs
    go acc pos (x :: xs) =
      if x == 0 then go acc pos xs
      else if x <= -100 then go (S acc) pos (x + 100 :: xs)
      else if 100 <= x then go (S acc) pos (x - 100 :: xs)
      else if x + pos < 0 then go (if pos == 0 then acc else S acc) (x + pos + 100) xs
      else if x + pos == 0 then go (S acc) (x + pos) xs
      else if 100 <= x + pos  then go (S acc) (x + pos - 100) xs
      else go acc (x + pos) xs

run : String → IO Unit
run fn = do
  printLn fn
  text <- readFile fn
  let xs = parse text
  let p1 = part1 xs
  printLn "part1 \{show p1}"
  let p2 = part2 xs
  printLn "part2 \{show p2}"

main : IO Unit
main = do
  run "aoc2025/day1/eg.txt"
  run "aoc2025/day1/input.txt"