(ns queens)

;; Aim of the program is to put N queens on a N x N board
;; (for example 8 queens on a 8 x 8 board ) avoiding each
;; queen to eat one of the others.

(defstruct queens :board :current-queen)


(defn next-solution-queens
  "Compute the next valid position of the queens
  return nil if no more solutions are avaiable."
  [queens]
  nil)

(defn next-solution-actual-queen
  "Compute the next valid position for the actual queen
  return nil if there is no valid solution."
  [queens]
  nil)

(declare diagonal-down-busy?, diagonal-up-busy?)

(defn line-busy?
  "Check if the line on wich the current queen is located is free"
  [queens]
  (let [{board :board current-queen :current-queen} queens
        line (nth board current-queen)]
    (> (count (filter #{line} board)) 1)))

(defn is-position-valid?
  "Return true if the position of the actual queen is valid
  returns false otherwise."
  [queens]
  (let [{board :board current-queen :current-queen} queens]
    (or (= current-queen 0)
        (not (or (line-busy? queens)
                 (diagonal-up-busy? queens)
                 (diagonal-down-busy? queens))))))