module Day2

import Prelude
import Node
import Aoc

parse : String → List (Int × Int)
parse text = map mkPair $ split text ","
  where
    mkPair : String → Int × Int
    mkPair t = case split t "-" of
      (a :: b :: Nil) => (stringToInt a, stringToInt b)
      bad => fatalError "BAD \{t}"

invalid : String → Bool
invalid s =
  let l = slen s
      h = l / 2
  in if h * 2 /= l then False
  else go 0 h
  where
    go : Int → Int → Bool
    go i h = if i == h
      then True
      else if sindex s i == sindex s (i + h) then go (i + 1) h else False

match : List Char → List Char → Bool
match pat cs = go pat cs
  where
    go : List Char → List Char → Bool
    go (p :: ps) (c :: cs) = if p == c then go ps cs else False
    go Nil Nil = True
    go Nil cs = go pat cs
    go (p :: ps) Nil = False

invalid' : String → Bool
invalid' s =
  let l = slen s
      h = l / 2
  in check (S Z) (cast h) $ unpack s
  where
    check : Nat → Nat → List Char → Bool
    check a h cs =
      if a > h then False else
        if match (take a cs) cs then True else check (S a) h cs

scan : (String → Bool) → Int → Int → Int → Int
scan invalid a b acc =
  let acc = if invalid (show a) then acc + a else acc in
  if a == b then acc else scan invalid (a + 1) b acc

part1 : String → Int
part1 text = foldl (\acc x => scan invalid (fst x) (snd x) acc) 0 $ parse text

part2 : String → Int
part2 text = foldl (\acc x => scan invalid' (fst x) (snd x) acc) 0 $ parse text

run : String -> IO Unit
run fn = do
  putStrLn fn
  text <- readFile fn
  printLn $ parse text
  putStrLn $ "part1 " ++ show (part1 text)
  putStrLn $ "part2 " ++ show (part2 text)

main : IO Unit
main = do
  run "aoc2025/day2/eg.txt"
  run "aoc2025/day2/input.txt"