import 'package:flutter/material.dart';
import 'package:flutter_bluetooth_serial/flutter_bluetooth_serial.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:permission_handler/permission_handler.dart';
import '../../../core/providers/bt_provider.dart';
import '../../widgets/main_nav.dart';
import '../../../core/logging/app_log.dart';

class BtPickerScreen extends ConsumerStatefulWidget {
  const BtPickerScreen({super.key});

  @override
  ConsumerState<BtPickerScreen> createState() => _BtPickerScreenState();
}

class _BtPickerScreenState extends ConsumerState<BtPickerScreen> {
  String? _error;
  bool _initDone = false;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_) => _initBluetooth());
  }

  bool _permissionsOk = false;

  Future<void> _initBluetooth() async {
    setState(() {
      _error = null;
      _initDone = false;
    });

    try {
      // Android 12+: BLUETOOTH_CONNECT is the only permission needed to list
      // paired devices and open an RFCOMM socket. On Android 11 and older
      // permission_handler reports it as granted. Scan/location are requested
      // but not required (we never run discovery).
      final statuses = await [
        Permission.bluetoothConnect,
        Permission.bluetoothScan,
        Permission.locationWhenInUse,
      ].request();

      final connect = statuses[Permission.bluetoothConnect];
      if (connect != null && !connect.isGranted && !connect.isLimited) {
        AppLog.w('Bluetooth permission not granted: $connect');
        if (!mounted) return;
        setState(() {
          _permissionsOk = false;
          _error = 'Bluetooth permission ("Nearby devices") was not granted.\n\n'
              'Go to Settings → Apps → HV BT Dashboard → Permissions.';
          _initDone = true;
        });
        if (connect.isPermanentlyDenied) await openAppSettings();
        return;
      }
      _permissionsOk = true;

      final btState = await FlutterBluetoothSerial.instance.state;
      if (btState != BluetoothState.STATE_ON) {
        await FlutterBluetoothSerial.instance.requestEnable();
        await Future<void>.delayed(const Duration(seconds: 1));
      }
    } catch (e, st) {
      AppLog.e('Bluetooth init failed', e, st);
      if (!mounted) return;
      setState(() => _error = 'Bluetooth init failed: $e');
    }

    if (!mounted) return;
    setState(() => _initDone = true);
    if (_permissionsOk) ref.invalidate(pairedDevicesProvider);
  }

  // ECU protocol is chosen once via Settings (or defaults to S300) and
  // persisted from there — no need to ask again on every connection. A
  // dialog here used to re-prompt "S300 or KPro?" on every single tap,
  // which was pure friction once the user had already told the app which
  // ECU they have.
  Future<void> _connect(BluetoothDevice device) async {
    if (ref.read(btProvider).isConnecting) return;
    await ref.read(btProvider.notifier).connect(device);
    if (!mounted) return;
    if (ref.read(btProvider).isConnected) {
      Navigator.of(context).pushReplacement(
        MaterialPageRoute(builder: (_) => const MainNav()),
      );
    }
  }

  @override
  Widget build(BuildContext context) {
    final btState = ref.watch(btProvider);
    // Do NOT touch the paired-device list before permission is granted:
    // on Android 12+ that call throws inside the Bluetooth plugin.
    final AsyncValue<List<BluetoothDevice>> devicesAsync = _permissionsOk
        ? ref.watch(pairedDevicesProvider)
        : const AsyncValue<List<BluetoothDevice>>.data([]);

    return Scaffold(
      appBar: AppBar(
        title: const Text('Connect to ECU'),
        actions: [
          IconButton(
            icon: const Icon(Icons.refresh),
            onPressed: _loading ? null : _initBluetooth,
          ),
        ],
      ),
      body: Column(
        children: [
          if (btState.status == BtStatus.error)
            _banner('Connection failed: ${btState.error}'),
          if (_error != null) _banner(_error!),
          Expanded(
            child: !_initDone
                ? const Center(child: CircularProgressIndicator())
                : devicesAsync.when(
                    loading: () => const Center(
                        child: CircularProgressIndicator()),
                    error: (e, _) =>
                        Center(child: _banner('Failed to load: $e')),
                    data: (devices) => devices.isEmpty
                        ? const Center(
                            child: Padding(
                              padding: EdgeInsets.all(24),
                              child: Text(
                                'No paired BT devices.\nPair your ECU in Android Settings first.',
                                textAlign: TextAlign.center,
                                style: TextStyle(color: Colors.grey),
                              ),
                            ),
                          )
                        : ListView.separated(
                            itemCount: devices.length,
                            separatorBuilder: (_, __) =>
                                const Divider(height: 1),
                            itemBuilder: (_, i) {
                              final d = devices[i];
                              final connecting = btState.isConnecting &&
                                  btState.deviceName ==
                                      (d.name ?? d.address);
                              return ListTile(
                                leading: const Icon(Icons.bluetooth),
                                title: Text(d.name ?? 'Unknown'),
                                subtitle: Text(d.address),
                                trailing: connecting
                                    ? const SizedBox(
                                        width: 20,
                                        height: 20,
                                        child: CircularProgressIndicator(
                                            strokeWidth: 2))
                                    : const Icon(
                                        Icons.arrow_forward_ios,
                                        size: 14),
                                onTap: connecting ? null : () => _connect(d),
                              );
                            },
                          ),
                  ),
          ),
        ],
      ),
    );
  }

  bool get _loading => !_initDone || ref.read(btProvider).isConnecting;

  Widget _banner(String msg) => Container(
        width: double.infinity,
        color: const Color(0xFF4A0000),
        padding: const EdgeInsets.all(12),
        child: Text(msg,
            style: const TextStyle(color: Colors.redAccent, fontSize: 12)),
      );
}