Austin Clojure 4/13 alphabet-cipher

coder.clj

(ns alphabet-cipher.coder)

(defn char->num [char]
  (- (int char) (int \a)))

(defn num->char [ch]
  (char (+ (int ch) (int \a))))

(defn mod26 [n]
  (mod n 26))

(defn encode-by [key char]
  (-> (char->num char)
      (+ (char->num key))
      (mod26)
      (num->char)))

(defn decode-by [key char]
  (-> (char->num char)
      (- (char->num key))
      (mod26)
      (num->char)))


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

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