Alphabet Cipher

coder.clj

(ns alphabet-cipher.coder)

(defn to-char [n]
  (char (+ (int \a) (mod n 26))))

(defn to-int [c]
  (- (int c) (int \a)))
  
(defn m [k s]
  (to-char (+ (to-int k)(to-int s))))

(defn rm [k s]
  (to-char (- (to-int s) (to-int k))))

(defn encode [keyword message]
  (apply str (map m (cycle keyword) message)))

(defn decode [keyword message]
  (apply str (map rm (cycle keyword) message)))

(defn inits [s]
  (when-let [ss (seq s)]
    (cons [] (map #(cons (first ss) %) (inits (rest ss))))))
                      
(defn uncycle [s]
  (let [len (count s)]
    (first (filter #(= (seq s) (take len (cycle %))) (rest (inits s))))))

(defn decypher [cypher message]
  (apply str (uncycle (apply str (map rm message cypher)))))