module Day9.Main where

import System.IO
import Data.List
import Data.List.Split

main :: IO ()
main = do
    putStrLn "Day 9"
    
    handle <- openFile "app/Day9/example" ReadMode
    contents <- hGetContents handle

    let r1 = part1 contents
    putStrLn $ "part 1: " ++ show r1

    let r2 = part2 contents
    putStrLn $ "part 2: " ++ show r2

data Direction = DUp | DDown | DLeft | DRight
                 deriving (Show)

data Heading = None | N | E | S | W | NE | SE | SW | NW

type Motion = (Int, Direction)
type Point = (Int, Int)
type Rope = (Point, Point) -- head, tail

instance Read Direction where
    readsPrec _ "R" = [(DRight, "")]
    readsPrec _ "L" = [(DLeft, "")]
    readsPrec _ "U" = [(DUp, "")]
    readsPrec _ "D" = [(DDown, "")]

toMotion :: [String] -> Motion
toMotion (a:b:_) = (read b, read a)

toHeading :: Rope -> Heading
toHeading ((hx,hy),(tx,ty))
 | hx == tx &&
   hy == ty = None

 | hx == tx &&
   hy <  ty = S
 | hx == tx &&
   hy >  ty = N
 | hy == ty &&
   hx <  tx = W
 | hy == ty &&
   hx >  tx = E
   
 | hx <  tx &&
   hy <  ty = SW
 | hx <  tx &&
   hy >  ty = NW
 | hx >  tx &&
   hy <  ty = SE
 | hx >  tx &&
   hy >  ty = NE

parseData :: String -> [Motion]
parseData = (map toMotion) . (map (splitOn " ")) . lines

expandMovement :: [Motion] -> [Direction]
expandMovement = concatMap (uncurry replicate)

doMovement :: Rope -> Direction -> Rope
doMovement rope DUp =
    case toHeading rope of
        None -> ((hx, hy+1), (tx, ty))
        
        N    -> ((hx, hy+1), (tx, ty+1))
        E    -> ((hx, hy+1), (tx, ty))
        S    -> ((hx, hy+1), (tx, ty))
        W    -> ((hx, hy+1), (tx, ty))
        
        NE   -> ((hx, hy+1), (tx+1, ty+1))
        SE   -> ((hx, hy+1), (tx, ty))
        SW   -> ((hx, hy+1), (tx, ty))
        NW   -> ((hx, hy+1), (tx-1, ty+1))
    where
        ((hx, hy), (tx, ty)) = rope

doMovement rope DDown =
    case toHeading rope of
        None -> ((hx, hy-1), (tx, ty))

        N    -> ((hx, hy-1), (tx, ty))
        E    -> ((hx, hy-1), (tx, ty))
        S    -> ((hx, hy-1), (tx, ty-1))
        W    -> ((hx, hy-1), (tx, ty))

        NE   -> ((hx, hy-1), (tx, ty))
        SE   -> ((hx, hy-1), (tx+1, ty-1))
        SW   -> ((hx, hy-1), (tx-1, ty-1))
        NW   -> ((hx, hy-1), (tx, ty))
    where
        ((hx, hy), (tx, ty)) = rope

doMovement rope DLeft =
    case toHeading rope of
        None -> ((hx-1, hy), (tx, ty))

        N    -> ((hx-1, hy), (tx, ty))
        E    -> ((hx-1, hy), (tx, ty))
        S    -> ((hx-1, hy), (tx, ty))
        W    -> ((hx-1, hy), (tx-1, ty))

        NE   -> ((hx-1, hy), (tx, ty))
        SE   -> ((hx-1, hy), (tx, ty))
        SW   -> ((hx-1, hy), (tx-1, ty-1))
        NW   -> ((hx-1, hy), (tx-1, ty+1))
    where
        ((hx, hy), (tx, ty)) = rope

doMovement rope DRight =
    case toHeading rope of
        None -> ((hx+1, hy), (tx, ty))

        N    -> ((hx+1, hy), (tx, ty))
        E    -> ((hx+1, hy), (tx+1, ty))
        S    -> ((hx+1, hy), (tx, ty))
        W    -> ((hx+1, hy), (tx, ty))

        NE   -> ((hx+1, hy), (tx+1, ty+1))
        SE   -> ((hx+1, hy), (tx+1, ty-1))
        SW   -> ((hx+1, hy), (tx, ty))
        NW   -> ((hx+1, hy), (tx, ty))
    where
        ((hx, hy), (tx, ty)) = rope

part1 contents = path
    where
        steps = expandMovement $ parseData contents
        step = take 2 steps
        (final, path) = foldr (\m (r, ps) -> let (h,t) = doMovement r m in ((h,t), (t:ps))) (((0,0),(0,0)),[(0,0)]) steps
part2 contents = 1