add timer widget, provider and util (format)

lib/pages/interval_page.dart

@@ -2,7 +2,9 @@ import 'dart:async';
 import 'package:audioplayers/audioplayers.dart';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
+import 'package:smoke_cess_app/providers/timer_provider.dart';
 import 'package:smoke_cess_app/widgets/popup_for_start_and_stop.dart';
+import 'package:smoke_cess_app/widgets/timer_widget.dart';
 
 import '../providers/input_provider.dart';
 
@@ -166,6 +168,11 @@ class _IntervalTimerPageState extends State<IntervalTimerPage> {
 
   @override
   Widget build(BuildContext context) {
+    return ChangeNotifierProvider(
+        create: (context) => TimerProvider(),
+        child: TimerWidget(
+          duration: Duration(seconds: 5),
+        ));
     return Center(
         child: ChangeNotifierProvider(
             create: (context) => InputProvider(),

lib/providers/timer_provider.dart

@@ -0,0 +1,23 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+
+class TimerProvider extends ChangeNotifier {
+  Timer? _timer;
+  bool started = false;
+  int get elapsedSeconds => _timer != null ? _timer!.tick : 0;
+
+  void startTimer(Duration duration) {
+    started = true;
+    print('starting timer');
+    _timer = Timer.periodic(const Duration(seconds: 1), ((timer) {
+      if (timer.tick >= duration.inSeconds) {
+        timer.cancel();
+        started = false;
+      }
+      notifyListeners();
+    }));
+  }
+
+  void stopTimer() => _timer?.cancel();
+}

lib/utils/timer_util.dart

@@ -0,0 +1,4 @@
+String formatTime(int seconds) {
+  Duration duration = Duration(seconds: seconds);
+  return '${duration.inMinutes.remainder(60).toString().padLeft(2, '0')}:${duration.inSeconds.remainder(60).toString().padLeft(2, '0')}';
+}

lib/widgets/timer_widget.dart

@@ -0,0 +1,25 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+import 'package:smoke_cess_app/providers/timer_provider.dart';
+import 'package:smoke_cess_app/utils/timer_util.dart';
+
+class TimerWidget extends StatelessWidget {
+  final Duration duration;
+  const TimerWidget({super.key, required this.duration});
+
+  @override
+  Widget build(BuildContext context) {
+    TimerProvider timerProvider = context.watch<TimerProvider>();
+    return Column(
+      mainAxisAlignment: MainAxisAlignment.center,
+      children: [
+        Text(formatTime(duration.inSeconds - timerProvider.elapsedSeconds)),
+        ElevatedButton(
+            onPressed: () => timerProvider.started
+                ? timerProvider.stopTimer()
+                : timerProvider.startTimer(duration),
+            child: Text(timerProvider.started ? 'Stop' : 'Start'))
+      ],
+    );
+  }
+}