UUIDv7 in Clojure

uuidv7.clj

(ns uuidv7
  (:require [clojure.string :as str])
  (:import (java.security SecureRandom)))

(defn gen-uuid-v7
  "Returns an UUIDv7 as a byte seq."
  []
  (let [rand-array (byte-array 10)]
    (.nextBytes (SecureRandom.) rand-array)
    (concat
      ;; timestamp
      (map byte (.toByteArray (biginteger (System/currentTimeMillis))))
      ;; version
      [(bit-or (bit-and (first rand-array) 0x0F) 0x70)]
      [(nth rand-array 1)]
      ;; variant
      [(bit-or (bit-and (nth rand-array 2) 0x3F) 0x80)]
      (drop 3 rand-array))))

(defn uuid-to-string
  "Formats a byte seq UUIDv7 to lowercase hex string with dashes."
  [uuid-bytes]
  (str/join "-"
            (map #(apply str %)
                 (let [indices (reductions + 0 [4 2 2 2 6])]
                   (map #(subvec (vec (map (partial format "%02x") uuid-bytes)) %1 %2)
                        (butlast indices)
                        (rest indices))))))