module Maskbits
( Maskbits(..),
  decrement,
  maskbits_from_string
) where

import Test.QuickCheck

-- | A type representing the number of bits in a CIDR netmask.
data Maskbits =
    Zero
  | One
  | Two
  | Three
  | Four
  | Five
  | Six
  | Seven
  | Eight
  | Nine
  | Ten
  | Eleven
  | Twelve
  | Thirteen
  | Fourteen
  | Fifteen
  | Sixteen
  | Seventeen
  | Eighteen
  | Nineteen
  | Twenty
  | TwentyOne
  | TwentyTwo
  | TwentyThree
  | TwentyFour
  | TwentyFive
  | TwentySix
  | TwentySeven
  | TwentyEight
  | TwentyNine
  | Thirty
  | ThirtyOne
  | ThirtyTwo
    deriving (Eq, Ord)


instance Show Maskbits where
  show Zero        = "0"
  show One         = "1"
  show Two         = "2"
  show Three       = "3"
  show Four        = "4"
  show Five        = "5"
  show Six         = "6"
  show Seven       = "7"
  show Eight       = "8"
  show Nine        = "9"
  show Ten         = "10"
  show Eleven      = "11"
  show Twelve      = "12"
  show Thirteen    = "13"
  show Fourteen    = "14"
  show Fifteen     = "15"
  show Sixteen     = "16"
  show Seventeen   = "17"
  show Eighteen    = "18"
  show Nineteen    = "19"
  show Twenty      = "20"
  show TwentyOne   = "21"
  show TwentyTwo   = "22"
  show TwentyThree = "23"
  show TwentyFour  = "24"
  show TwentyFive  = "25"
  show TwentySix   = "26"
  show TwentySeven = "27"
  show TwentyEight = "28"
  show TwentyNine  = "29"
  show Thirty      = "30"
  show ThirtyOne   = "31"
  show ThirtyTwo   = "32"


instance Arbitrary Maskbits where
  arbitrary =
    elements [ Zero,
               One,
               Two,
               Three,
               Four,
               Five,
               Six,
               Seven,
               Eight,
               Nine,
               Ten,
               Eleven,
               Twelve,
               Thirteen,
               Fourteen,
               Fifteen,
               Sixteen,
               Seventeen,
               Eighteen,
               Nineteen,
               Twenty,
               TwentyOne,
               TwentyTwo,
               TwentyThree,
               TwentyFour,
               TwentyFive,
               TwentySix,
               TwentySeven,
               TwentyEight,
               TwentyNine,
               Thirty,
               ThirtyOne,
               ThirtyTwo ]



-- | There are only 32 bits in an IPv4 address, so there
--   can't be more bits than that in the mask.
maskbits_from_int :: Int -> Maybe Maskbits
maskbits_from_int 0  = Just Zero
maskbits_from_int 1  = Just One
maskbits_from_int 2  = Just Two
maskbits_from_int 3  = Just Three
maskbits_from_int 4  = Just Four
maskbits_from_int 5  = Just Five
maskbits_from_int 6  = Just Six
maskbits_from_int 7  = Just Seven
maskbits_from_int 8  = Just Eight
maskbits_from_int 9  = Just Nine
maskbits_from_int 10 = Just Ten
maskbits_from_int 11 = Just Eleven
maskbits_from_int 12 = Just Twelve
maskbits_from_int 13 = Just Thirteen
maskbits_from_int 14 = Just Fourteen
maskbits_from_int 15 = Just Fifteen
maskbits_from_int 16 = Just Sixteen
maskbits_from_int 17 = Just Seventeen
maskbits_from_int 18 = Just Eighteen
maskbits_from_int 19 = Just Nineteen
maskbits_from_int 20 = Just Twenty
maskbits_from_int 21 = Just TwentyOne
maskbits_from_int 22 = Just TwentyTwo
maskbits_from_int 23 = Just TwentyThree
maskbits_from_int 24 = Just TwentyFour
maskbits_from_int 25 = Just TwentyFive
maskbits_from_int 26 = Just TwentySix
maskbits_from_int 27 = Just TwentySeven
maskbits_from_int 28 = Just TwentyEight
maskbits_from_int 29 = Just TwentyNine
maskbits_from_int 30 = Just Thirty
maskbits_from_int 31 = Just ThirtyOne
maskbits_from_int 32 = Just ThirtyTwo
maskbits_from_int _  = Nothing


-- | Convert a String to Maskbits, if possible.
maskbits_from_string :: String -> Maybe Maskbits
maskbits_from_string s =
  case (reads s :: [(Int, String)]) of
    []   -> Nothing
    x:_ -> maskbits_from_int (fst x)



-- | Maskbits are just natural numbers, this returns the previous one.
decrement :: Maskbits -> Maskbits
decrement Zero = Zero
decrement One = Zero
decrement Two = One
decrement Three = Two
decrement Four = Three
decrement Five = Four
decrement Six = Five
decrement Seven = Six
decrement Eight = Seven
decrement Nine = Eight
decrement Ten = Nine
decrement Eleven = Ten
decrement Twelve = Eleven
decrement Thirteen = Twelve
decrement Fourteen = Thirteen
decrement Fifteen = Fourteen
decrement Sixteen = Fifteen
decrement Seventeen = Sixteen
decrement Eighteen = Seventeen
decrement Nineteen = Eighteen
decrement Twenty = Nineteen
decrement TwentyOne = Twenty
decrement TwentyTwo = TwentyOne
decrement TwentyThree = TwentyTwo
decrement TwentyFour = TwentyThree
decrement TwentyFive = TwentyFour
decrement TwentySix = TwentyFive
decrement TwentySeven = TwentySix
decrement TwentyEight = TwentySeven
decrement TwentyNine = TwentyEight
decrement Thirty = TwentyNine
decrement ThirtyOne = Thirty
decrement ThirtyTwo = ThirtyOne