;;; cube-scrambler.el --- Rubik's cube scrambler

;; Copyright (C) Jonathan Lamothe

;; Author: Jonathan Lamothe <jonathan@jlamothe.net>
;; Package-Version: 0.0

;; This file is not part of GNU Emacs.

;;; Code:

(defvar cube-faces "UDLRFB")

(defun cube-scramble (moves)
  "Generates a list of random scramnles for a 3x3 Rubik's cube and displays it.

MOVES represents the number of moves in the list."
  (interactive "p")
  (message (mapconcat 'identity (cube-build-scramble moves) " ")))

(defun cube-build-scramble (moves)
  "Generates a list of random moves for a 3x3 Rubik's cube

MOVES os the number of moves to generate.  The algorithm will not
generate a sequence that moves the same face twice in a row."
  (let (result last-face)
    (while (> moves 0)
      (setq last-face (cube-random-face last-face))
      (push (cube-random-turn last-face) result)
      (setq moves (1- moves )))
    result))

(defun cube-random-face (&optional last-face)
  "Generates a random cube face

If supplied, LAST-FACE will be excluded as a possibility."
  (let ((faces (cube-filter cube-faces last-face)))
    (elt faces (random (length faces)))))

(defun cube-random-turn (face)
  "Generates a random turn directio  for a given face

FACE is a character representing the face to be turned."
  (let ((suffix (pcase (random 3)
                  (0 "")
                  (1 "'")
                  (2 "2"))))
    (format "%c%s" face suffix)))

(defun cube-filter (str char)
  "Filters all instances of a character from a string"
  (seq-filter (lambda (c) (not (equal c char))) str))

;;; cube-scrambler.el ends here