module Octet where

import Test.HUnit
import Test.QuickCheck

import Bit

-- An Octet consists of eight bits. For our purposes, the most
-- significant bit will come "first." That is, b1 is in the 2^7
-- place while b8 is in the 2^0 place.
data Octet = None | Octet { b1 :: Bit,
                            b2 :: Bit,
                            b3 :: Bit,
                            b4 :: Bit,
                            b5 :: Bit,
                            b6 :: Bit,
                            b7 :: Bit,
                            b8 :: Bit }
           deriving (Eq)


instance Show Octet where
    show Octet.None = "None"
    show oct = show (octet_to_int oct)


instance Arbitrary Octet where
    arbitrary = do
      a1 <- arbitrary :: Gen Bit
      a2 <- arbitrary :: Gen Bit
      a3 <- arbitrary :: Gen Bit
      a4 <- arbitrary :: Gen Bit
      a5 <- arbitrary :: Gen Bit
      a6 <- arbitrary :: Gen Bit
      a7 <- arbitrary :: Gen Bit
      a8 <- arbitrary :: Gen Bit
      return (Octet a1 a2 a3 a4 a5 a6 a7 a8)

    coarbitrary _ = variant 0


-- Convert each bit to its integer value, and multiply by the
-- appropriate power of two. Sum them up, and we should get an integer
-- between 0 and 255.
octet_to_int :: Octet -> Int
octet_to_int x =
    128 * (bit_to_int (b1 x)) +
    64  * (bit_to_int (b2 x)) +
    32  * (bit_to_int (b3 x)) +
    16  * (bit_to_int (b4 x)) +
    8   * (bit_to_int (b5 x)) +
    4   * (bit_to_int (b6 x)) +
    2   * (bit_to_int (b7 x)) +
    1   * (bit_to_int (b8 x))



octet_from_int :: Int -> Octet
octet_from_int x
    | (x < 0) || (x > 255) = Octet.None
    | otherwise = (Octet a1 a2 a3 a4 a5 a6 a7 a8)
    where
      a1 = if (x >= 128) then One else Zero
      a2 = if ((x `mod` 128) >= 64) then One else Zero
      a3 = if ((x `mod` 64)  >= 32) then One else Zero
      a4 = if ((x `mod` 32)  >= 16) then One else Zero
      a5 = if ((x `mod` 16)  >= 8)  then One else Zero
      a6 = if ((x `mod` 8)   >= 4)  then One else Zero
      a7 = if ((x `mod` 4)   >= 2)  then One else Zero
      a8 = if ((x `mod` 2)   == 1)  then One else Zero


octet_from_string :: String -> Octet
octet_from_string s =
    case (reads s :: [(Int, String)]) of
      []   -> Octet.None
      x:_ -> octet_from_int (fst x)


-- The octet with the least possible value.
min_octet :: Octet
min_octet = Octet Zero Zero Zero Zero Zero Zero Zero Zero


-- The octet with the greatest possible value.
max_octet :: Octet
max_octet = Octet One One One One One One One One



-- HUnit Tests
test_octet_from_int1 :: Test
test_octet_from_int1 =
    TestCase $ assertEqual "octet_from_int 128 should parse as 10000000" oct1 (octet_from_int 128)
    where
      oct1 = Octet One Zero Zero Zero Zero Zero Zero Zero


octet_tests :: [Test]
octet_tests = [ test_octet_from_int1 ]