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

-- A type representing the number of bits in a CIDR netmask.
data Maskbits = None
              | 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 None        = "None"
    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"



-- 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 -> Maskbits
maskbits_from_int 0  = Zero
maskbits_from_int 1  = One
maskbits_from_int 2  = Two
maskbits_from_int 3  = Three
maskbits_from_int 4  = Four
maskbits_from_int 5  = Five
maskbits_from_int 6  = Six
maskbits_from_int 7  = Seven
maskbits_from_int 8  = Eight
maskbits_from_int 9  = Nine
maskbits_from_int 10 = Ten
maskbits_from_int 11 = Eleven
maskbits_from_int 12 = Twelve
maskbits_from_int 13 = Thirteen
maskbits_from_int 14 = Fourteen
maskbits_from_int 15 = Fifteen
maskbits_from_int 16 = Sixteen
maskbits_from_int 17 = Seventeen
maskbits_from_int 18 = Eighteen
maskbits_from_int 19 = Nineteen
maskbits_from_int 20 = Twenty
maskbits_from_int 21 = TwentyOne
maskbits_from_int 22 = TwentyTwo
maskbits_from_int 23 = TwentyThree
maskbits_from_int 24 = TwentyFour
maskbits_from_int 25 = TwentyFive
maskbits_from_int 26 = TwentySix
maskbits_from_int 27 = TwentySeven
maskbits_from_int 28 = TwentyEight
maskbits_from_int 29 = TwentyNine
maskbits_from_int 30 = Thirty
maskbits_from_int 31 = ThirtyOne
maskbits_from_int 32 = ThirtyTwo
maskbits_from_int _ = None


maskbits_from_string :: String -> Maskbits
maskbits_from_string s =
    case (reads s :: [(Int, String)]) of
      []   -> None
      x:_ -> maskbits_from_int (fst x)



decrement :: Maskbits -> Maskbits
decrement None = None
decrement Zero = None
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