Added Uuid generator class

Signed-off-by: Andreas Fahrecker <AndreasFahrecker@gmail.com>

lib/uuid.dart

@@ -0,0 +1,26 @@
+import 'dart:math';
+
+class Uuid {
+  final Random _random = Random();
+
+  /// Generate a version 4 (random) uuid. This is a uuid scheme that only uses
+  /// random numbers as the source of the generated uuid.
+  String generateV4() {
+    // Generate xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx / 8-4-4-4-12.
+    final special = 8 + _random.nextInt(4);
+
+    return '${_bitsDigits(16, 4)}${_bitsDigits(16, 4)}-'
+        '${_bitsDigits(16, 4)}-'
+        '4${_bitsDigits(12, 3)}-'
+        '${_printDigits(special, 1)}${_bitsDigits(12, 3)}-'
+        '${_bitsDigits(16, 4)}${_bitsDigits(16, 4)}${_bitsDigits(16, 4)}';
+  }
+
+  String _bitsDigits(int bitCount, int digitCount) =>
+      _printDigits(_generateBits(bitCount), digitCount);
+
+  int _generateBits(int bitCount) => _random.nextInt(1 << bitCount);
+
+  String _printDigits(int value, int count) =>
+      value.toRadixString(16).padLeft(count, '0');
+}