import Data.List
import Data.List.Split

type Rule = [Int]
type Update = [Int]

relevant :: Update -> Rule -> Bool
relevant upd (b:a:[]) = (b `elem` upd) && (a `elem` upd)

abides :: Update -> Rule -> Bool
abides [] _ = False
abides (h:t) r@(a:[])
  | h == a = True
  | otherwise = abides t r
abides (h:t) r@(b:a:[])
  | h == b = abides t [a]
  | otherwise = abides t r

middle :: [Int] -> Int
middle arr = arr !! (length arr `div` 2)

valid :: [Rule] -> Update -> Bool
valid rules update =
  all (abides update) $ filter (relevant update) rules

apply :: [Rule] -> Int -> Int -> Ordering
apply rules a b
  | [a,b] `elem` rules = LT
  | [b,a] `elem` rules = GT
  | otherwise = EQ

part11 :: Int -> [Rule] -> [Update] -> Int
part11 acc _ [] = acc
part11 acc rules (h:t)
  | valid rules h = part11 (acc + (middle h)) rules t
  | otherwise     = part11 acc rules t

part1 :: [Rule] -> [Update] -> Int
part1 rules updates =
  part11 0 rules updates

part21 :: Int -> [Rule] -> [Update] -> Int
part21 acc _ [] = acc
part21 acc rules (h:t)
  | valid rules h = part21 acc rules t
  | otherwise =
    let rrules = filter (relevant h) rules
        sfun = apply rrules
        inc = middle $ sortBy (sfun) h in
          part21 (acc + inc) rules t

part2 :: [Rule] -> [Update] -> Int
part2 rules updates =
  part21 0 rules updates

main = do
  file <- readFile "day05.input"
  let lns = lines file
      rulesin:updatesin:[] = splitOn [""] lns
      rules = map (map (read::String->Int)) $ map (splitOn "|") rulesin
      updates = map (map (read::String -> Int)) $ map (splitOn ",") updatesin
  putStrLn ("Part 1: " ++ (show $ part1 rules updates))
  putStrLn ("Part 2: " ++ (show $ part2 rules updates))