core.clj

(import '[java.nio.file Path Files FileSystem FileSystems StandardCopyOption FileVisitor FileVisitResult])

(defn ->path [path]
  (if (instance? Path path)
    path
    (.getPath (FileSystems/getDefault) path (into-array String []))))

(defn copy [from to]
  (Files/copy (->path from) (->path to) (into-array [StandardCopyOption/COPY_ATTRIBUTES])))

(defn copying-visitor [source dest]
  (reify FileVisitor
    (preVisitDirectory [_ dir _]
      (copy dir (.resolve dest (.relativize source dir)))
      FileVisitResult/CONTINUE)
    (visitFile [_ file _]
      (copy file (.resolve dest (.relativize source file)))
      FileVisitResult/CONTINUE)
    (postVisitDirectory [_ dir _]
      FileVisitResult/CONTINUE)))

(defn copy-dir [source dest]
  (let [source (->path source)
        dest (->path dest)]
    (Files/walkFileTree source (copying-visitor source dest))))