fix: smooth scan RSSI readings

lib/controller/bluetooth.dart

@@ -45,6 +45,7 @@ class BluetoothController {
   BluetoothController(this._ble);
 
   static const int defaultMtu = 64;
+  static const Duration _rssiAverageWindow = Duration(milliseconds: 500);
 
   final FlutterReactiveBle _ble;
 
@@ -52,6 +53,7 @@ class BluetoothController {
   StreamSubscription<DiscoveredDevice>? _scanResultsSubscription;
   Timer? _scanTimeout;
   final Map<String, DiscoveredDevice> _scanResultsById = {};
+  final RssiAverager _rssiAverager = RssiAverager(window: _rssiAverageWindow);
   final _scanResultsSubject =
       BehaviorSubject<List<DiscoveredDevice>>.seeded(const []);
   final _isScanningSubject = BehaviorSubject<bool>.seeded(false);
@@ -102,6 +104,7 @@ class BluetoothController {
 
       _scanTimeout?.cancel();
       _scanResultsById.clear();
+      _rssiAverager.clear();
       _scanResultsSubject.add(const []);
       _isScanningSubject.add(true);
 
@@ -112,7 +115,12 @@ class BluetoothController {
         requireLocationServicesEnabled: requireLocationServicesEnabled,
       )
           .listen((device) {
-        _scanResultsById[device.id] = device;
+        final smoothedRssi = _rssiAverager.addSample(
+          device.id,
+          device.rssi,
+          DateTime.now(),
+        );
+        _scanResultsById[device.id] = device.copyWith(rssi: smoothedRssi);
         _scanResultsSubject
             .add(_scanResultsById.values.toList(growable: false));
       }, onError: (Object error, StackTrace st) {
@@ -394,3 +402,26 @@ class BluetoothController {
     return Ok(null);
   }
 }
+
+class RssiAverager {
+  RssiAverager({required this.window});
+
+  final Duration window;
+  final Map<String, List<(DateTime, int)>> _samplesByDeviceId = {};
+
+  int addSample(String deviceId, int rssi, DateTime timestamp) {
+    final cutoff = timestamp.subtract(window);
+    final samples = _samplesByDeviceId.putIfAbsent(deviceId, () => []);
+
+    samples
+      ..removeWhere((sample) => sample.$1.isBefore(cutoff))
+      ..add((timestamp, rssi));
+
+    final total = samples.fold<int>(0, (sum, sample) => sum + sample.$2);
+    return (total / samples.length).round();
+  }
+
+  void clear() {
+    _samplesByDeviceId.clear();
+  }
+}