;;;; random.lisp
;;; Time-stamp: <2019-05-27 14:53:38 m.buchmann>
;;;
;;; A short sketch of some random data generating functions.
;;;

(ql:quickload "alexandria")

;; * Choosing a random element from a given list.
(defun random-draw (list &aux (len (length list)) (pos (random len)))
  "Returns a random element from LIST."
  (nth pos list))

;;; * Generating a random element
(defun random-element (type &key (radix 10) (case :up))
  "Returns a random element of type :digit (depending on :radix) or
  :character (case given by :case :up, :down or :both). Limited to
7bit ASCII characters from A to z."
  (let ((char-range (ecase case
                      (:up   (alexandria:iota 26 :start 65))
                      (:down (alexandria:iota 26 :start 97))
                      (:both (append (alexandria:iota 26 :start 65)
                                     (alexandria:iota 26 :start 97))))))
      (ecase type
        (:digit (random radix))
        (:character (code-char (random-draw char-range))))))

(defun random-list (len &key (type :digit) (radix 10) (case :up))
  "Returns a list of length LEN filled with random elements of TYPE :digit or :character."
  (loop :for i from 0 below len
        :collect (random-element type :radix radix :case case)))

(defun random-string (len &key (case :up) &aux (result (make-array len :element-type 'character)))
  "Returns a random string of length LEN and :case (:up, :down or :both)."
  (loop :for i :from 0 :below len
        :do (setf (aref result i) (random-element :character :case case)))
  result)