Optimize sound latency with preloading, add startup welcome chime, and improve Android vibration haptics

flutter_app/lib/feedback_helper.dart

@@ -2,37 +2,88 @@ import 'package:flutter/services.dart';
 import 'package:audioplayers/audioplayers.dart';
 import 'package:vibration/vibration.dart';
 import 'package:flutter/foundation.dart' show kIsWeb, debugPrint;
+import 'dart:io' show Platform;
 
 class AppFeedback {
-  static final AudioPlayer _player = AudioPlayer();
+  static final Map<String, AudioPlayer> _players = {
+    'click.mp3': AudioPlayer(),
+    'select.mp3': AudioPlayer(),
+    'success.mp3': AudioPlayer(),
+    'error.mp3': AudioPlayer(),
+  };
 
-  /// Play a sound from assets/sounds/
+  static bool _initialized = false;
+
+  /// Preload sounds to achieve zero latency
+  static void init() {
+    if (_initialized) return;
+    try {
+      _players.forEach((key, player) {
+        player.setReleaseMode(ReleaseMode.stop);
+        player.setSource(AssetSource('sounds/$key'));
+      });
+      _initialized = true;
+    } catch (e) {
+      debugPrint('Error initializing AppFeedback: $e');
+    }
+  }
+
+  /// Play a sound from assets/sounds/ with zero delay
   static Future<void> playSound(String fileName) async {
     try {
-      // AudioPlayer play from assets/sounds/fileName
-      await _player.play(AssetSource('sounds/$fileName'));
+      if (!_initialized) {
+        init();
+      }
+      final player = _players[fileName];
+      if (player != null) {
+        // Stop/seek and resume for instant audio
+        await player.seek(Duration.zero);
+        await player.resume();
+      } else {
+        // Fallback for dynamically added files
+        final tempPlayer = AudioPlayer();
+        await tempPlayer.play(AssetSource('sounds/$fileName'));
+      }
     } catch (e) {
-      // Web might throw security exception if player triggers before user interaction
-      // or other runtime issues. Catching prevents app crashes.
       debugPrint('Audio playback error for $fileName: $e');
     }
   }
 
+  /// Helper to check Android platform safely
+  static bool get _isAndroid => !kIsWeb && Platform.isAndroid;
+
+  /// Trigger native vibration for Android with customized duration (in milliseconds)
+  static void _triggerVibration(int duration) async {
+    if (kIsWeb) return;
+    try {
+      if (_isAndroid) {
+        if (await Vibration.hasVibrator() == true) {
+          Vibration.vibrate(duration: duration);
+        }
+      }
+    } catch (e) {
+      debugPrint('Vibration error: $e');
+    }
+  }
+
   /// Light haptic feedback + subtle click sound
   static void click() {
     HapticFeedback.lightImpact();
+    _triggerVibration(30);
     playSound('click.mp3');
   }
 
   /// Medium haptic + selection sound
   static void select() {
     HapticFeedback.mediumImpact();
+    _triggerVibration(60);
     playSound('select.mp3');
   }
 
   /// Celebration sound + strong haptic vibration
   static void success() {
     HapticFeedback.heavyImpact();
+    _doubleVibrate();
     playSound('success.mp3');
   }
 
@@ -45,21 +96,25 @@ class AppFeedback {
   /// Light haptic feedback (e.g. chip selections)
   static void lightHaptic() {
     HapticFeedback.lightImpact();
+    _triggerVibration(30);
   }
 
   /// Medium haptic feedback
   static void mediumHaptic() {
     HapticFeedback.mediumImpact();
+    _triggerVibration(60);
   }
 
   /// Heavy haptic feedback
   static void heavyHaptic() {
     HapticFeedback.heavyImpact();
+    _triggerVibration(100);
   }
 
   /// Subtle haptic feedback (e.g. screen navigation)
   static void subtleHaptic() {
     HapticFeedback.selectionClick();
+    _triggerVibration(20);
   }
 
   /// Double vibrate pattern using vibration package
@@ -69,7 +124,6 @@ class AppFeedback {
         // Double vibrate pattern: wait 0, vibrate 100ms, wait 100ms, vibrate 100ms
         Vibration.vibrate(pattern: [0, 100, 100, 100]);
       } else {
-        // Fallback to native HapticFeedback
         HapticFeedback.mediumImpact();
       }
     } catch (e) {

flutter_app/lib/main.dart

@@ -1,9 +1,11 @@
 import 'package:flutter/material.dart';
 import 'theme.dart';
 import 'screens/welcome_screen.dart';
+import 'feedback_helper.dart';
 
 void main() {
   WidgetsFlutterBinding.ensureInitialized();
+  AppFeedback.init();
   runApp(const PozoApp());
 }
 

flutter_app/lib/screens/welcome_screen.dart

@@ -76,6 +76,11 @@ class _WelcomeScreenState extends State<WelcomeScreen> with SingleTickerProvider
     );
 
     _controller.forward();
+    Future.delayed(const Duration(milliseconds: 300), () {
+      if (mounted) {
+        AppFeedback.success();
+      }
+    });
   }
 
   Future<void> _initMobileNumberDetection() async {