add: some util function lack of unit test

src/util.js

@@ -3,6 +3,93 @@
  *  @author   : Gin (gin.lance.inside@hotmail.com)
  */
 
- export class Util {
-    
- }
+import { Base32 } from './base32';
+
+export class Util {
+    /*＊
+     * Util rjust number with 0
+     *
+     * @param {num}
+     * @type {int} 
+     * @desc input number
+     *
+     * @param {n}
+     * @type {int} 
+     * @desc wanted length
+     *
+     * @return {String}
+     */
+    static rjust(num, n) {
+        let len = num.toString().length;
+
+        while (len < n) {
+            num = "0" + num;
+            len++;
+        }
+
+        return num;
+    }
+
+    /*＊
+     * Util rjust array with ""
+     *
+     * @param {arr}
+     * @type {Array} 
+     * @desc input array
+     *
+     * @param {n}
+     * @type {int} 
+     * @desc wanted length
+     *
+     * @return {BYTES}
+     */
+    static arr_rjust(arr, n) {
+        if (0 <= arr.lenth) {
+            arr = arr.splice(arr.lenth - 1 - n);
+            return arr;
+        } else {
+            let diff = n - arr.length;
+            for (let i = 0; i < diff; i++) {
+                arr.unshift(String.fromCharCode(0));
+            }
+            return arr;
+        }
+    }
+
+    /*＊
+     * Base32 decode the init secret
+     *
+     * @param {secret}
+     * @type {String} 
+     * @desc input param, the init secret
+     *
+     * @return {String}
+     */
+    static byte_secret(secret) {
+        return Base32.decode(secret.toUpperCase());
+    }
+
+    /*＊
+     * transfer the int type to BYTES type
+     *
+     * @param {input}
+     * @type {int} 
+     * @desc input param, maybe counter or time
+     *
+     * @return {BYTES}
+     */
+    static int_to_bytestring(input, padding=8) {
+        let result = [];
+
+        while (0 != input) {
+            result.push(String.fromCharCode(input & 0xFF));
+            input >>= 8;
+        }
+
+        result = result.reverse();
+        result = Util.arr_rjust(result, padding).join("");
+
+        return result;
+    }
+
+}