(ns paging-task.ad-hoc)

;;; idea:
;;; drop fixed number of points (1,2,3, current-1,current,current+1,last-2,last-1,last)
;;; sort
;;; remove duplicated
;;; insert separator

(defn- insert-separator [separator coll]
  (loop [result []
         c coll]
    (if (empty? c)
      result
      (if (empty? (rest c))
        (conj result (first c))
        (if (= (inc (first c)) (second c))
          (recur (conj result (first c)) (rest c))
          (recur (conj (conj result (first c)) separator) (rest c)))))))

(defn get-pages [total current]
  (let [intervals [[1 (min total 3)]
                   [(max 1 (dec current)) (min total (inc current))]
                   [(max 1 (- total 2)) total]]
        points (mapcat (fn [[a b]] (range a (inc b))) intervals)]
    (->> points
         (sort)
         (distinct)
         (insert-separator "...")
         (map str))))