substring java string with emoji

emoji-subs.clj

  (import 'java.text.BreakIterator)

  (defn break-index-seq [s]
    (let [iter (doto (BreakIterator/getCharacterInstance)
                 (.setText s))
          c (.first iter)
          -seq (fn f [c iter]
                 (lazy-seq (when (not= c BreakIterator/DONE)
                             (cons c (f (.next iter) iter)))))]
      (-seq c iter)))

  (defn string-with-emoji-subs [v s e]
    (let [idxs (break-index-seq v)
          s (max 0 s)
          e (min (dec (count idxs)) e)]
      (.substring v (nth idxs s) (nth idxs e))))

  (string-with-emoji-subs "🍓🍓🍓" 0 0)
  (string-with-emoji-subs "🍓🍓🍓" 0 1)
  (string-with-emoji-subs "🍓🍓🍓" 0 2)
  (string-with-emoji-subs "🍓🍓🍓" 0 3)
  (string-with-emoji-subs "🍓🍓🍓" 0 4)