module Bead9 where

isJust :: Maybe a -> Bool
isJust (Just _) = True
isJust_ = False

fromJust :: Maybe a -> a
fromJust (Just x) = x

catMaybes :: [Maybe a] -> [a]
catMaybes [] = []
catMaybes (x:xs)
    | isJust x = (fromJust x):catMaybes xs
    | otherwise = catMaybes xs

mapMaybe :: (a -> Maybe b) -> [a] -> [b]
mapMaybe f =  catMaybes . map f

safeHead :: [a] -> Maybe a
safeHead[] = Nothing
safeHead (x:xs) = Just x

type Username = String
type Password = String

data Privilege = Simple | Admin
  deriving (Eq, Show)

data Cookie = LoggedOut | LoggedIn Username Privilege
  deriving (Eq, Show)

data Entry = Entry Password Privilege [Username]
  deriving (Eq, Show)

type Database = [(Username, Entry)]

richard, charlie, carol, david, kate :: (Username, Entry)
richard = ("Richard", Entry "password1" Admin  ["Kate"])
charlie = ("Charlie", Entry "password2" Simple ["Carol"])
carol   = ("Carol",   Entry "password3" Simple ["David", "Charlie"])
david   = ("David",   Entry "password4" Simple ["Carol"])
kate    = ("Kate",    Entry "password5" Simple ["Richard"])

testDB :: Database
testDB = [ richard, charlie, carol, david, kate ]

testDBWithoutCarol :: Database
testDBWithoutCarol =
  [ ("Richard", Entry "password1" Admin  ["Kate"])
  , ("Charlie", Entry "password2" Simple [])
  , ("David",   Entry "password4" Simple [])
  , ("Kate",    Entry "password5" Simple ["Richard"])
  ]

password :: Entry -> Password
password (Entry pass k l) = pass

privilege :: Entry -> Privilege
privilege (Entry k x l) = x

friends :: Entry -> [Username]
friends (Entry k x l) = l

mkCookie :: Username -> Password -> Entry -> Cookie
mkCookie user pass (Entry pa pri t)
      | pass == pa = LoggedIn user pri
      | otherwise = LoggedOut

login :: Username -> Password -> Database -> Cookie
login user pas [(us, db)] = toLogin $ lookup(user, us) db where
  toLogin :: Maybe Entry -> Cookie
  toLogin Nothing = LoggedOut
  toLogin (Just p) = mkCookie user ps db


--login user pass db =toCookie $ lookup(user,pass) db where
  --toCookie :: Maybe Privilege -> Cookie
  --toCookie Nothing = LoggedOut
  --toCookie (Just p) = LoggedIn user p