Add Bluetooth permission and adapter state handling for Android and iOS

lib/screens/scan_screen.dart

@@ -2,7 +2,11 @@ import 'package:flutter/material.dart';
 
 import '../models/scooter_device.dart';
 import '../scooters/apollo_scooter.dart';
+import 'dart:async';
+import 'dart:io';
+
 import '../services/ble_client.dart';
+import '../services/ble_permissions.dart';
 import '../services/demo_ble_client.dart';
 import '../theme.dart';
 import 'scooter_screen.dart';
@@ -16,8 +20,14 @@ class ScanScreen extends StatefulWidget {
   State<ScanScreen> createState() => _ScanScreenState();
 }
 
-class _ScanScreenState extends State<ScanScreen> {
+/// What is stopping us from scanning, if anything.
+enum _Gate { checking, permissionDenied, permissionPermanentlyDenied, bluetoothOff, unsupported, ready }
+
+class _ScanScreenState extends State<ScanScreen> with WidgetsBindingObserver {
   Stream<List<ScooterDevice>>? _scan;
+  _Gate _gate = _Gate.checking;
+  StreamSubscription<BleAdapterState>? _adapterSub;
+  bool _requesting = false;
 
   /// Development path: list every BLE device so a scooter that does not
   /// advertise F1F0/F2F0 can still be selected and classified after GATT
@@ -27,10 +37,86 @@ class _ScanScreenState extends State<ScanScreen> {
   @override
   void initState() {
     super.initState();
-    _scan = widget.ble.scan();
+    WidgetsBinding.instance.addObserver(this);
+    _prepare(request: true);
   }
 
-  void _restart() => setState(() => _scan = widget.ble.scan());
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    _adapterSub?.cancel();
+    super.dispose();
+  }
+
+  /// Re-check when coming back from system settings or the Bluetooth toggle.
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state == AppLifecycleState.resumed && _gate != _Gate.ready) {
+      _prepare(request: false);
+    }
+  }
+
+  /// Permission first, then adapter state, then scan.
+  Future<void> _prepare({required bool request}) async {
+    if (_requesting) return;
+    _requesting = true;
+    try {
+      final access = request ? await BlePermissions.request() : await BlePermissions.status();
+      if (!mounted) return;
+      switch (access) {
+        case BleAccess.denied:
+          _setGate(_Gate.permissionDenied);
+          return;
+        case BleAccess.permanentlyDenied:
+          _setGate(_Gate.permissionPermanentlyDenied);
+          return;
+        case BleAccess.unsupported:
+          _setGate(_Gate.unsupported);
+          return;
+        case BleAccess.granted:
+          break;
+      }
+      _watchAdapter();
+    } finally {
+      _requesting = false;
+    }
+  }
+
+  void _watchAdapter() {
+    _adapterSub ??= widget.ble.adapterState.listen((s) {
+      if (!mounted) return;
+      switch (s) {
+        case BleAdapterState.on:
+          if (_gate != _Gate.ready) {
+            _setGate(_Gate.ready);
+            _restart();
+          }
+        case BleAdapterState.off:
+        case BleAdapterState.unknown:
+          _setGate(_Gate.bluetoothOff);
+        case BleAdapterState.unauthorized:
+          _setGate(_Gate.permissionPermanentlyDenied);
+        case BleAdapterState.unsupported:
+          _setGate(_Gate.unsupported);
+      }
+    });
+  }
+
+  void _setGate(_Gate g) {
+    if (_gate == g) return;
+    setState(() {
+      _gate = g;
+      if (g != _Gate.ready) _scan = null;
+    });
+  }
+
+  void _restart() {
+    if (_gate != _Gate.ready) {
+      _prepare(request: true);
+      return;
+    }
+    setState(() => _scan = widget.ble.scan());
+  }
 
   Future<void> _connect(ScooterDevice device, {BleClient? ble}) async {
     setState(() => _scan = null);
@@ -89,7 +175,9 @@ class _ScanScreenState extends State<ScanScreen> {
               ),
             ),
             Expanded(
-              child: _scan == null
+              child: _gate != _Gate.ready
+                  ? _gateView()
+                  : _scan == null
                   ? const SizedBox.shrink()
                   : StreamBuilder<List<ScooterDevice>>(
                       stream: _scan,
@@ -152,6 +240,54 @@ class _ScanScreenState extends State<ScanScreen> {
   }
 }
 
+extension on _ScanScreenState {
+  Widget _gateView() {
+    final android = Platform.isAndroid;
+    return switch (_gate) {
+      _Gate.checking => const Center(child: CircularProgressIndicator()),
+      _Gate.permissionDenied => _Empty(
+          icon: Icons.bluetooth_rounded,
+          title: 'Bluetooth permission needed',
+          message: android
+              ? 'OpenMotion needs the Nearby devices permission to find and talk to your scooter. '
+                  'Scan results are never used for location.'
+              : 'OpenMotion needs Bluetooth access to find and talk to your scooter.',
+          action: FilledButton(
+            onPressed: () => _prepare(request: true),
+            child: const Text('Allow Bluetooth'),
+          ),
+        ),
+      _Gate.permissionPermanentlyDenied => _Empty(
+          icon: Icons.bluetooth_disabled_rounded,
+          title: 'Bluetooth permission blocked',
+          message: android
+              ? 'Nearby devices access was denied. Enable it for OpenMotion in system settings, then come back.'
+              : 'Bluetooth access is off for OpenMotion. Enable it in Settings, then come back.',
+          action: FilledButton(
+            onPressed: BlePermissions.openSettings,
+            child: const Text('Open settings'),
+          ),
+        ),
+      _Gate.bluetoothOff => _Empty(
+          icon: Icons.bluetooth_disabled_rounded,
+          title: 'Bluetooth is off',
+          message: android
+              ? 'Turn on Bluetooth to scan for your scooter.'
+              : 'Turn on Bluetooth in Control Center or Settings to scan for your scooter.',
+          action: android
+              ? FilledButton(onPressed: widget.ble.turnOn, child: const Text('Turn on Bluetooth'))
+              : null,
+        ),
+      _Gate.unsupported => const _Empty(
+          icon: Icons.error_outline_rounded,
+          title: 'Bluetooth unavailable',
+          message: 'This device does not support Bluetooth Low Energy.',
+        ),
+      _Gate.ready => const SizedBox.shrink(),
+    };
+  }
+}
+
 class _DeviceCard extends StatelessWidget {
   const _DeviceCard({required this.device, required this.onConnect});
 
@@ -229,7 +365,8 @@ class _Empty extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Padding(
+    return Container(
+      width: double.infinity,
       padding: const EdgeInsets.fromLTRB(24, 48, 24, 24),
       child: Column(
         children: [

lib/services/ble_client.dart

@@ -8,6 +8,8 @@ import 'protocol_log.dart';
 
 enum BleConnectionState { disconnected, connected }
 
+enum BleAdapterState { unknown, unsupported, off, on, unauthorized }
+
 /// Thin boundary between OpenScooter and the underlying BLE plugin.
 ///
 /// OpenScooter v1 supports EXACTLY ONE active scooter connection at a time.
@@ -17,6 +19,13 @@ enum BleConnectionState { disconnected, connected }
 /// Protocol code never imports the BLE plugin directly, so protocol tests run
 /// with `flutter test` and a fake subclass, without hardware.
 abstract class BleClient {
+  /// Current Bluetooth adapter state, emitting on change. Fakes default to on.
+  Stream<BleAdapterState> get adapterState => Stream.value(BleAdapterState.on);
+
+  /// Asks the OS to enable Bluetooth. Only Android supports this; elsewhere it
+  /// is a no-op and the UI must direct the user to system settings.
+  Future<void> turnOn() async {}
+
   /// Streams the current set of visible devices. Scanning starts on listen
   /// and stops when the subscription is cancelled.
   Stream<List<ScooterDevice>> scan();
@@ -63,6 +72,27 @@ class FlutterBleClient extends BleClient {
   @override
   Stream<BleConnectionState> get connectionState => _connState.stream;
 
+  @override
+  Stream<BleAdapterState> get adapterState =>
+      fbp.FlutterBluePlus.adapterState.map((s) => switch (s) {
+            fbp.BluetoothAdapterState.on => BleAdapterState.on,
+            fbp.BluetoothAdapterState.off ||
+            fbp.BluetoothAdapterState.turningOff ||
+            fbp.BluetoothAdapterState.turningOn =>
+              BleAdapterState.off,
+            fbp.BluetoothAdapterState.unauthorized => BleAdapterState.unauthorized,
+            fbp.BluetoothAdapterState.unavailable => BleAdapterState.unsupported,
+            fbp.BluetoothAdapterState.unknown => BleAdapterState.unknown,
+          });
+
+  @override
+  Future<void> turnOn() async {
+    if (defaultTargetPlatform == TargetPlatform.android) {
+      _log('ADAPTER turnOn requested');
+      await fbp.FlutterBluePlus.turnOn();
+    }
+  }
+
   @override
   Stream<List<ScooterDevice>> scan() {
     late StreamController<List<ScooterDevice>> controller;
@@ -70,12 +100,7 @@ class FlutterBleClient extends BleClient {
 
     Future<void> start() async {
       try {
-        var adapter = await fbp.FlutterBluePlus.adapterState.first;
-        if (adapter != fbp.BluetoothAdapterState.on &&
-            defaultTargetPlatform == TargetPlatform.android) {
-          await fbp.FlutterBluePlus.turnOn();
-        }
-        adapter = await fbp.FlutterBluePlus.adapterState
+        await fbp.FlutterBluePlus.adapterState
             .where((s) => s == fbp.BluetoothAdapterState.on)
             .first
             .timeout(const Duration(seconds: 10));

lib/services/ble_permissions.dart

@@ -0,0 +1,75 @@
+import 'dart:io';
+
+import 'package:device_info_plus/device_info_plus.dart';
+import 'package:permission_handler/permission_handler.dart';
+
+/// Outcome of a Bluetooth permission check or request.
+enum BleAccess {
+  /// Everything granted. Bluetooth adapter state is checked separately.
+  granted,
+
+  /// The user declined but can be asked again.
+  denied,
+
+  /// The user declined with "don't ask again" (Android) or in Settings (iOS).
+  /// Only the system settings screen can fix this.
+  permanentlyDenied,
+
+  /// The platform reported Bluetooth as unavailable.
+  unsupported,
+}
+
+/// Requests the runtime permissions OpenMotion needs to scan and connect.
+///
+/// Android 12+ (API 31): BLUETOOTH_SCAN and BLUETOOTH_CONNECT, shown to the
+/// user as "Nearby devices". Android 11 and below: legacy BLE scanning needs
+/// location while in use. iOS: the single Bluetooth permission, which the OS
+/// prompts for the first time CoreBluetooth is touched.
+class BlePermissions {
+  BlePermissions._();
+
+  static int? _androidSdk;
+
+  static Future<int> androidSdk() async {
+    if (!Platform.isAndroid) return 0;
+    return _androidSdk ??= (await DeviceInfoPlugin().androidInfo).version.sdkInt;
+  }
+
+  static Future<List<Permission>> _needed() async {
+    if (Platform.isAndroid) {
+      final sdk = await androidSdk();
+      return sdk >= 31
+          ? const [Permission.bluetoothScan, Permission.bluetoothConnect]
+          : const [Permission.locationWhenInUse];
+    }
+    if (Platform.isIOS || Platform.isMacOS) return const [Permission.bluetooth];
+    return const [];
+  }
+
+  /// Checks without prompting.
+  static Future<BleAccess> status() async {
+    final statuses = <PermissionStatus>[];
+    for (final p in await _needed()) {
+      statuses.add(await p.status);
+    }
+    return _combine(statuses);
+  }
+
+  /// Prompts for anything not yet granted.
+  static Future<BleAccess> request() async {
+    final needed = await _needed();
+    if (needed.isEmpty) return BleAccess.granted;
+    final results = await needed.request();
+    return _combine(results.values.toList());
+  }
+
+  static BleAccess _combine(List<PermissionStatus> statuses) {
+    if (statuses.any((s) => s.isPermanentlyDenied || s.isRestricted)) {
+      return BleAccess.permanentlyDenied;
+    }
+    if (statuses.any((s) => s.isDenied)) return BleAccess.denied;
+    return BleAccess.granted;
+  }
+
+  static Future<bool> openSettings() => openAppSettings();
+}