module Main where

type Title = String
type Videolist = [(Title,(Int,Int))] --[(title,(available,rent))]

movies::Videolist
movies = [("Am Limit",(1,0)), ("Kill Bill vol. 1", (3,1)),("Matrix",(2,2)),("Das Matterhorn",(3,1))]

rentable :: Title -> Videolist -> Bool
rentable _ [] =  False
rentable title ((t,(a,r)):rest) = if title == t then a>r else rentable title rest

hasFilm :: Title -> Videolist -> Bool
hasFilm _ [] = False
hasFilm title ((t,(_,_)):rest) = (t == title) || hasFilm title rest

rent:: Title -> Videolist -> Videolist
rent _ [] = error "Film nicht vorhanden"
rent x ((t,(a,r)):rest) | not (hasFilm x ((t,(a,r)):rest)) = error "Film nicht vorhanden"
                        | not (rentable x ((t,(a,r)):rest)) = error "Film nicht verfuegbar"
                        | otherwise = if x == t then (t,(a,r+1)):rest else (t, (a, r)) : rent x rest


addFilm::Title -> Videolist -> Videolist
addFilm title [] = [(title, (1, 0))]
addFilm title ((t,(a,r)):rest) = if title == t then (t,(a+1,r)):rest else (t, (a, r)) : addFilm title rest

insert:: Title -> Videolist -> (Videolist,Bool)
insert title liste | not (hasFilm title liste)  = ((title, (1, 0)) : liste,False)
                   | otherwise = (addFilm title liste,True)

showVideolistItem::Title -> Videolist -> String
showVideolistItem _ [] = "Film nicht in der Liste"
showVideolistItem title ((t,(a,r)):rest) = if title ==  t
                                                        then t ++ " (" ++ show r ++
  " Exemplare verliehen, " ++
    (if a == r then "keine" else show (a - r) ) ++ " Exemplare auf Lager)"
                                                        else showVideolistItem title rest

state :: Videolist -> (Int, Int)
state [] = (0,0)
state ((_,(a,r)):rest) = ??

main::IO()
main = do
        putStr "search Am Limit"