looking for stream replay

stream_demo.dart

import 'package:flutter/material.dart';
import 'dart:async';

void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

typedef S ReduceFn<S, T>(S stream, T input);
StreamTransformer makeReduceTransformer(reduceFn, seed) {
  var state = seed;
  return new StreamTransformer.fromHandlers(handleData: (s, sink) {
    state = reduceFn(state, s);
    sink.add(state);
  });
}

class _MyHomePageState extends State<MyHomePage> {
  StreamController<int> _clickStream = new StreamController<int>.broadcast(sync: true);
  Stream<int> _stateStream;
  Stream<String> _fizzBuzzStream;

  @override
  void initState() {
    super.initState();
    int stateFunc(int previous, int input) {
      return previous + input;
    }

    _stateStream = _clickStream.stream.transform(makeReduceTransformer(stateFunc, 0));
    _fizzBuzzStream = _stateStream.map((int val) {
      if (val % 5 == 0) {
        return 'fizz';
      }
      if (val % 10 == 0) {
        return 'buzz';
      }
      return '--';
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(
              'You have pushed the button this many times:',
            ),
            new StreamBuilder(
              stream: _stateStream,
              builder: (context, snapshot) => new Text(
                    '${snapshot.data ?? 0}',
                    style: Theme.of(context).textTheme.display1,
                  ),
            ),
            new StreamBuilder(
              stream: _fizzBuzzStream,
              builder: (context, snapshot) => new Text(
                snapshot.data ?? '--',
                style: Theme.of(context).textTheme.display2,
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: () => _clickStream.add(1),
        tooltip: 'Increment',
        child: new Icon(Icons.add),
    )
    );
  }
}