feat: new shifter types and better gear ratio editor

lib/service/shifter_service.dart

@@ -20,6 +20,8 @@ class ShifterService {
   Stream<CentralStatus> get statusStream => _statusController.stream;
 
   static const int _gearRatioSlots = 32;
+  static const int _defaultGearIndexOffset = _gearRatioSlots;
+  static const int _gearRatioPayloadBytes = _gearRatioSlots + 1;
   static const double _maxGearRatio = 255 / 64;
   static const int _gearRatioWriteMtu = 64;
 
@@ -56,7 +58,7 @@ class ShifterService {
     return writeCommand(UniversalShifterCommand.connectToDevice);
   }
 
-  Future<Result<List<double>>> readGearRatios() async {
+  Future<Result<GearRatiosData>> readGearRatios() async {
     final readRes = await _bluetooth.readCharacteristic(
       buttonDeviceId,
       universalShifterControlServiceUuid,
@@ -67,25 +69,43 @@ class ShifterService {
     }
 
     final raw = readRes.unwrap();
-    if (raw.length > _gearRatioSlots) {
+    if (raw.length > _gearRatioPayloadBytes) {
       return bail(
-        'Invalid gear ratio payload length: expected at most $_gearRatioSlots, got ${raw.length}',
+        'Invalid gear ratio payload length: expected at most $_gearRatioPayloadBytes, got ${raw.length}',
       );
     }
 
-    final normalizedRaw = List<int>.filled(_gearRatioSlots, 0, growable: false);
+    final normalizedRaw = List<int>.filled(
+      _gearRatioPayloadBytes,
+      0,
+      growable: false,
+    );
     for (var i = 0; i < raw.length; i++) {
       normalizedRaw[i] = raw[i];
     }
 
-    final ratios = normalizedRaw
-        .where((v) => v > 0)
-        .map((v) => _decodeGearRatio(v))
-        .toList(growable: false);
-    return Ok(ratios);
+    final ratios = <double>[];
+    for (var i = 0; i < _gearRatioSlots; i++) {
+      final value = normalizedRaw[i];
+      if (value == 0) {
+        break;
+      }
+      ratios.add(_decodeGearRatio(value));
+    }
+
+    final defaultIndexRaw = normalizedRaw[_defaultGearIndexOffset];
+    final defaultGearIndex = ratios.isEmpty
+        ? 0
+        : defaultIndexRaw.clamp(0, ratios.length - 1).toInt();
+    return Ok(
+      GearRatiosData(
+        ratios: ratios,
+        defaultGearIndex: defaultGearIndex,
+      ),
+    );
   }
 
-  Future<Result<void>> writeGearRatios(List<double> ratios) async {
+  Future<Result<void>> writeGearRatios(GearRatiosData data) async {
     final mtuResult =
         await _bluetooth.requestMtu(buttonDeviceId, mtu: _gearRatioWriteMtu);
     if (mtuResult.isErr()) {
@@ -93,12 +113,16 @@ class ShifterService {
           'Could not request MTU before writing gear ratios: ${mtuResult.unwrapErr()}');
     }
 
-    final payload = List<int>.filled(_gearRatioSlots, 0, growable: false);
+    final payload =
+        List<int>.filled(_gearRatioPayloadBytes, 0, growable: false);
+    final ratios = data.ratios;
     final limit =
         ratios.length < _gearRatioSlots ? ratios.length : _gearRatioSlots;
     for (var i = 0; i < limit; i++) {
       payload[i] = _encodeGearRatio(ratios[i]);
     }
+    payload[_defaultGearIndexOffset] =
+        limit == 0 ? 0 : data.defaultGearIndex.clamp(0, limit - 1).toInt();
 
     return _bluetooth.writeCharacteristic(
       buttonDeviceId,
@@ -177,3 +201,13 @@ class ShifterService {
     return raw / 64.0;
   }
 }
+
+class GearRatiosData {
+  const GearRatiosData({
+    required this.ratios,
+    required this.defaultGearIndex,
+  });
+
+  final List<double> ratios;
+  final int defaultGearIndex;
+}