fix: stabilize live notch filter

open_wearable/lib/widgets/sensors/values/sensor_chart/axis_display_filter.dart

@@ -41,13 +41,18 @@ class _AxisDisplayFilterCache {
 }
 
 class _AxisDisplayFilter {
+  static const int _initialIntervalCount = 8;
+  static const int _rateCheckIntervalCount = 16;
+
   final _AxisFilterConfig config;
   final double timestampScale;
   final List<_IirFilterStage> _highPassStages;
   final List<_IirFilterStage> _lowPassStages;
   final List<_IirFilterStage> _notchStages;
+  final List<double> _measuredIntervals = <double>[];
 
   int? _previousTimestamp;
+  double? _designDt;
 
   _AxisDisplayFilter({
     required this.config,
@@ -61,7 +66,10 @@ class _AxisDisplayFilter {
       return input;
     }
 
-    final dt = _timeDeltaSeconds(timestamp);
+    final dt = _stableTimeDelta(_timeDeltaSeconds(timestamp));
+    if (dt == null) {
+      return input;
+    }
     var output = input;
     for (final stage in _highPassStages) {
       output = stage.apply(output, dt);
@@ -78,6 +86,12 @@ class _AxisDisplayFilter {
 
   void reset() {
     _previousTimestamp = null;
+    _designDt = null;
+    _measuredIntervals.clear();
+    _resetStages();
+  }
+
+  void _resetStages() {
     for (final stage in _highPassStages) {
       stage.reset();
     }
@@ -89,6 +103,44 @@ class _AxisDisplayFilter {
     }
   }
 
+  double? _stableTimeDelta(double measuredDt) {
+    if (measuredDt <= 0 || !measuredDt.isFinite) {
+      return _designDt;
+    }
+
+    _measuredIntervals.add(measuredDt);
+    final designDt = _designDt;
+    if (designDt == null) {
+      if (_measuredIntervals.length < _initialIntervalCount) {
+        return null;
+      }
+      _designDt = _medianInterval(_measuredIntervals);
+      _measuredIntervals.clear();
+      return _designDt;
+    }
+
+    if (_measuredIntervals.length >= _rateCheckIntervalCount) {
+      final recentDt = _medianInterval(_measuredIntervals);
+      _measuredIntervals.clear();
+      // Keep IIR coefficients fixed through timestamp jitter. A sustained rate
+      // change needs new coefficients and a reset of the filter state.
+      if (recentDt < designDt * 0.8 || recentDt > designDt * 1.25) {
+        _designDt = recentDt;
+        _resetStages();
+      }
+    }
+    return _designDt;
+  }
+
+  static double _medianInterval(List<double> intervals) {
+    final sorted = intervals.toList()..sort();
+    final middle = sorted.length ~/ 2;
+    if (sorted.length.isOdd) {
+      return sorted[middle];
+    }
+    return (sorted[middle - 1] + sorted[middle]) / 2;
+  }
+
   double _timeDeltaSeconds(int timestamp) {
     final previousTimestamp = _previousTimestamp;
     _previousTimestamp = timestamp;

open_wearable/test/widgets/sensors/values/sensor_chart_notch_test.dart

@@ -0,0 +1,185 @@
+import 'dart:collection';
+import 'dart:math';
+
+import 'package:fl_chart/fl_chart.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:open_earable_flutter/open_earable_flutter.dart';
+import 'package:open_wearable/view_models/sensor_data_provider.dart';
+import 'package:open_wearable/widgets/sensors/values/sensor_chart.dart';
+import 'package:provider/provider.dart';
+
+void main() {
+  testWidgets('50 Hz notch remains bounded with irregular sample intervals',
+      (tester) async {
+    final provider = _FakeSensorDataProvider();
+    provider.addSamples(22);
+
+    await _enableNotch(tester, provider);
+
+    void expectStableOutput() {
+      final chart = tester.widget<LineChart>(find.byType(LineChart));
+      expect(
+        chart.data.lineBarsData.single.spots.every(
+          (spot) => spot.y.isFinite && spot.y.abs() < 5,
+        ),
+        isTrue,
+        reason: 'A bounded input must not produce a growing notch output.',
+      );
+      expect(tester.takeException(), isNull);
+    }
+
+    expectStableOutput();
+    for (var batch = 0; batch < 25; batch++) {
+      provider.addSamples(50);
+      await tester.pump();
+      expectStableOutput();
+    }
+  });
+
+  testWidgets('50 Hz notch still attenuates a regularly sampled 50 Hz tone',
+      (tester) async {
+    final provider = _FakeSensorDataProvider(intervalsMs: const [5]);
+    provider.addSamples(400);
+
+    await _pumpChart(tester, provider);
+    final rawMean = _recentMeanAbsoluteValue(tester);
+    await _openNotchSettings(tester);
+    final filteredMean = _recentMeanAbsoluteValue(tester);
+
+    expect(filteredMean, lessThan(rawMean * 0.5));
+    expect(tester.takeException(), isNull);
+  });
+
+  testWidgets('50 Hz notch adapts when the sensor sampling rate changes',
+      (tester) async {
+    final provider = _FakeSensorDataProvider(intervalsMs: const [10]);
+    provider.addSamples(200);
+    await _enableNotch(tester, provider);
+
+    provider.useIntervals(const [5]);
+    provider.addSamples(400);
+    await tester.pump();
+
+    expect(_recentMeanAbsoluteValue(tester), lessThan(0.3));
+    expect(tester.takeException(), isNull);
+  });
+}
+
+Future<void> _enableNotch(
+  WidgetTester tester,
+  _FakeSensorDataProvider provider,
+) async {
+  await _pumpChart(tester, provider);
+  await _openNotchSettings(tester);
+}
+
+Future<void> _pumpChart(
+  WidgetTester tester,
+  _FakeSensorDataProvider provider,
+) async {
+  await tester.pumpWidget(
+    ChangeNotifierProvider<SensorDataProvider>.value(
+      value: provider,
+      child: const MaterialApp(
+        home: Scaffold(
+          body: SizedBox(height: 400, child: SensorChart()),
+        ),
+      ),
+    ),
+  );
+}
+
+Future<void> _openNotchSettings(WidgetTester tester) async {
+  await tester.tap(find.text('X'));
+  await tester.pumpAndSettle();
+  await tester.ensureVisible(find.text('Notch filter'));
+  await tester.tap(find.byType(Switch).last);
+  await tester.pumpAndSettle();
+}
+
+double _recentMeanAbsoluteValue(WidgetTester tester) {
+  final chart = tester.widget<LineChart>(find.byType(LineChart));
+  final spots = chart.data.lineBarsData.single.spots;
+  final recent = spots.skip(spots.length - 100);
+  return recent.fold<double>(0, (sum, spot) => sum + spot.y.abs()) / 100;
+}
+
+class _FakeSensor extends Sensor<SensorDoubleValue> {
+  const _FakeSensor()
+      : super(
+          sensorName: 'Accelerometer',
+          chartTitle: 'Accelerometer',
+          shortChartTitle: 'Accel',
+        );
+
+  @override
+  List<String> get axisNames => const ['X'];
+
+  @override
+  List<String> get axisUnits => const ['g'];
+
+  @override
+  Stream<SensorDoubleValue> get sensorStream => const Stream.empty();
+}
+
+class _FakeWearable implements Wearable {
+  @override
+  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
+}
+
+class _FakeSensorDataProvider extends ChangeNotifier
+    implements SensorDataProvider {
+  List<int> _intervalsMs;
+
+  _FakeSensorDataProvider({
+    List<int> intervalsMs = const [5, 10, 15, 10],
+  }) : _intervalsMs = intervalsMs;
+
+  int _latestTimestamp = 0;
+  int _sampleIndex = 0;
+
+  @override
+  final Sensor sensor = const _FakeSensor();
+
+  @override
+  final Wearable wearable = _FakeWearable();
+
+  @override
+  final Queue<SensorValue> sensorValues = Queue<SensorValue>();
+
+  @override
+  int get timeWindow => 5;
+
+  @override
+  int get displayTimestamp => sensorValues.last.timestamp;
+
+  void useIntervals(List<int> intervalsMs) {
+    _intervalsMs = intervalsMs;
+    _sampleIndex = 0;
+  }
+
+  void addSamples(int count) {
+    for (var i = 0; i < count; i++) {
+      _latestTimestamp += _intervalsMs[_sampleIndex % _intervalsMs.length];
+      _sampleIndex++;
+      sensorValues.add(
+        SensorDoubleValue(
+          values: [
+            sin(2 * pi * 50 * _latestTimestamp / 1000) +
+                0.2 * sin(2 * pi * 7 * _latestTimestamp / 1000),
+          ],
+          timestamp: _latestTimestamp,
+        ),
+      );
+    }
+    while (sensorValues.isNotEmpty &&
+        sensorValues.first.timestamp < _latestTimestamp - 5000) {
+      sensorValues.removeFirst();
+    }
+    notifyListeners();
+  }
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
+}