-- Informatics 1 - Functional Programming
-- Tutorial 2
--
-- Week 4 - due: 13/14 Oct.

import Data.Char
import Data.List
import Test.QuickCheck


-- 1.
rotate :: Int -> [Char] -> [Char]
rotate n []                          = error "Cannot rotate empty list"
rotate n xs |n <= length xs && n > 0 = drop n xs ++ take n xs
            |n <= 0                  = error "You cannot rotate a string by 0 or by a negative number."
            |n > length xs           = error "n cannot be bigger than your string."



-- 2.
-- (b) It takes the modulus of the number by the length of the string
-- if it is too large or negative it will return 0, which will end
-- in doing rotate l str == str which is true.

prop_rotate :: Int -> String -> Bool
prop_rotate k str = rotate (l - m) (rotate m str) == str
                        where l = length str
                              m = if l == 0 then 0 else k `mod` l

-- 3.


makeKey :: Int -> [(Char, Char)]
makeKey n  = zip ['A'..'Z'] (rotate n ['A'..'Z'])


-- 4.
-- unzip the 2 lists, try if k is equal to the first term of my list
-- if not drop the first
lookUp :: Char -> [(Char, Char)] -> Char
lookup c []                 = c
lookUp c  ((x,y):xs) | c==x = y
                     | c/=x = lookUp c xs


-- 5.
encipher :: Int -> Char -> Char
encipher n c = lookUp c (makeKey n)

-- 6.
normalize :: String -> String
normalize (xs)  = [toUpper x | x <- xs, isAlpha x || isDigit x]

-- 7.
encipherStr :: Int -> String -> String
encipherStr = undefined

-- 8.
reverseKey :: [(Char, Char)] -> [(Char, Char)]
reverseKey [] = []
reverseKey ((x,y):xs) = (y,x) : reverseKey (xs)

-- 9.
decipher :: Int -> Char -> Char
decipher = undefined

decipherStr :: Int -> String -> String
decipherStr = undefined

-- 10.
prop_cipher :: Int -> String -> Property
prop_cipher = undefined

-- 11.
contains :: String -> String -> Bool
contains = undefined

-- 12.
candidates :: String -> [(Int, String)]
candidates = undefined



-- Optional Material

-- 13.
splitEachFive :: String -> [String]
splitEachFive = undefined

-- 14.
prop_transpose :: String -> Bool
prop_transpose = undefined

-- 15.
encrypt :: Int -> String -> String
encrypt = undefined

-- 16.
decrypt :: Int -> String -> String
decrypt = undefined

-- Challenge (Optional)

-- 17.
countFreqs :: String -> [(Char, Int)]
countFreqs = undefined

-- 18
freqDecipher :: String -> [String]
freqDecipher = undefined