module Zurg where

import Search
import List( (\\), delete, sort)


data Toy = Buzz | Hamm | Rex | Woody  deriving (Eq,Ord,Show)
data Pos = L | R                      deriving (Eq,Show)
type Group = [Toy]
type BridgePos = (Pos,Group)
type Move = Either Toy Group

toys :: [Toy]
toys = [Buzz,Hamm,Rex,Woody]

time :: Toy -> Int
time Buzz  = 5
time Woody = 10
time Rex   = 20
time Hamm  = 25

duration :: [Move] -> Int
duration = sum . map (either time (maximum . map time))

backw :: Group -> [(Move,BridgePos)]
backw xs = [(Left x,(L,sort (x:(toys \\ xs)))) | x <- xs]

forw :: Group -> [(Move,BridgePos)]
forw xs = [(Right [x,y],(R,delete y ys)) | 
              x <- xs,let ys=delete x xs, y <- ys, x<y]

instance SearchProblem BridgePos Move where
  trans (L,l)  = forw l
  trans (R,l)  = backw (toys \\ l)
  isSolution (ms,s) = s == (R,[]) && duration ms <= 60

solution :: [Move]
(solution,_):_ = solutions (L,toys)