module Lib
    ( 
        createAlphabetFromText,
        encryptCaesar,
        decryptCaesar,
        textToBits,
        bitsToText
    ) where

import Data.Char (ord, chr)
import Data.Bits (testBit)

createAlphabetFromText :: String -> [Char]
createAlphabetFromText [] = []
createAlphabetFromText (x:xs)
    | x `elem` alphabet = alphabet
    | otherwise     = x : alphabet
  where
    alphabet = createAlphabetFromText xs

indexOf :: (Eq t) => [t] -> t -> Int
indexOf [] _ = -1
indexOf (x : xs) target
  | x == target = 0
  | otherwise = 1 + indexOf xs target

encryptCaesar :: [Char] -> Int -> String -> String
encryptCaesar alphabet shift text = map caesarChar text
  where
    caesarChar c = alphabet !! ((indexOf alphabet c + shift) `mod` length alphabet)

decryptCaesar :: [Char] -> Int -> String -> String
decryptCaesar alphabet shift = 
  encryptCaesar alphabet (alphabetLength - (shift `mod` alphabetLength)) 
  where
    alphabetLength = length alphabet

textToBits :: String -> [Int]
textToBits = concatMap charToBits
    where charToBits c = [ if testBit (ord c) i then 1 else 0 | i <- [7,6..0] ]    

bitsToText :: [Int] -> String
bitsToText [] = []
bitsToText bits = (chr $ bitsToInt (take 8 bits)) : bitsToText (drop 8 bits)
    where
        bitsToInt charBits = 
            sum [bit * (2 ^ index) | (bit, index) <- zip charBits [7 :: Int, 6 .. 0]]