import 'dart:async';
import 'dart:convert';

import 'package:flutter_blue_plus/flutter_blue_plus.dart';
import 'package:permission_handler/permission_handler.dart';

import '../../../generated/constants.pbenum.dart';
import '../../../generated/network_config.pb.dart';
import '../../../generated/sec0.pb.dart';
import '../../../generated/session.pb.dart';

class BleScanResult {
  const BleScanResult({
    required this.deviceId,
    required this.name,
    required this.rssi,
  });

  final String deviceId;
  final String name;
  final int rssi;
}

class BleProvisioner {
  // Default service UUID from ESP-IDF scheme_ble.c (bytes reversed from LSB-first array).
  // Verify this matches by scanning and logging serviceUuids on first test.
  static const _serviceUuid = '1775244d-6b43-439b-877c-060f2d9bed07';

  // UUID 0x2901 — User Description GATT descriptor; maps endpoint names to chars.
  static const _userDescUuid = '2901';

  BluetoothDevice? _connectedDevice;

  Stream<BleScanResult> scan() async* {
    await _requestScanPermissions();

    await FlutterBluePlus.startScan(
      withServices: [Guid(_serviceUuid)],
      timeout: const Duration(seconds: 30),
    );

    await for (final results in FlutterBluePlus.scanResults) {
      for (final r in results) {
        final name = r.device.platformName;
        if (name.startsWith('anchor_')) {
          yield BleScanResult(
            deviceId: r.device.remoteId.str,
            name: name,
            rssi: r.rssi,
          );
        }
      }
    }
  }

  Future<void> stopScan() => FlutterBluePlus.stopScan();

  Future<void> provision(
    String deviceId, {
    required String ssid,
    required String wifiPassword,
    String? mqttHost,
    int? mqttPort,
  }) async {
    await _requestConnectPermissions();

    final device = BluetoothDevice.fromId(deviceId);
    _connectedDevice = device;

    await device.connect(timeout: const Duration(seconds: 15));

    try {
      await device.requestMtu(512);
      final services = await device.discoverServices();

      final service = services.firstWhere(
        (s) => s.uuid == Guid(_serviceUuid),
        orElse: () => throw Exception('Provisioning service not found'),
      );

      final charMap = await _buildCharMap(service);

      await _probeVersion(charMap);
      await _initSession(charMap);
      await _setWifiConfig(charMap, ssid: ssid, password: wifiPassword);
      await _applyWifiConfig(charMap);

      if (mqttHost != null) {
        await _sendMqttConfig(charMap, host: mqttHost, port: mqttPort ?? 1883);
      }
    } finally {
      await device.disconnect();
      _connectedDevice = null;
    }
  }

  void dispose() {
    FlutterBluePlus.stopScan();
    _connectedDevice?.disconnect();
    _connectedDevice = null;
  }

  // ---------------------------------------------------------------------------
  // Protocol steps
  // ---------------------------------------------------------------------------

  // Reads the User Description (0x2901) descriptor on each characteristic to
  // build a map of endpoint name -> characteristic
  Future<Map<String, BluetoothCharacteristic>> _buildCharMap(
      BluetoothService service) async {
    final map = <String, BluetoothCharacteristic>{};
    for (final char in service.characteristics) {
      for (final desc in char.descriptors) {
        if (desc.uuid == Guid(_userDescUuid)) {
          try {
            final value = await desc.read();
            final name = utf8.decode(value, allowMalformed: true).trim();
            if (name.isNotEmpty) map[name] = char;
          } catch (_) {}
          break;
        }
      }
    }
    return map;
  }

  Future<void> _probeVersion(
      Map<String, BluetoothCharacteristic> charMap) async {
    final char = _require(charMap, 'proto-ver');
    final resp = await _writeRead(char, utf8.encode('ESP'));
    try {
      final json = jsonDecode(utf8.decode(resp)) as Map<String, dynamic>;
      final prov = json['prov'] as Map<String, dynamic>?;
      if (prov != null) {
        // ignore: avoid_print
        print('[BleProvisioner] device ver=${prov['ver']} cap=${prov['cap']}');
      }
    } catch (_) {}
  }

  Future<void> _initSession(
      Map<String, BluetoothCharacteristic> charMap) async {
    final char = _require(charMap, 'prov-session');
    final request = SessionData(
      secVer: SecSchemeVersion.SecScheme0,
      sec0: Sec0Payload(
        msg: Sec0MsgType.S0_Session_Command,
        sc: S0SessionCmd(),
      ),
    );
    final respBytes = await _writeRead(char, request.writeToBuffer());
    final resp = SessionData.fromBuffer(respBytes);
    final status = resp.sec0.sr.status;
    if (status != Status.Success) {
      throw Exception('Session init failed: $status');
    }
  }

  Future<void> _setWifiConfig(
    Map<String, BluetoothCharacteristic> charMap, {
    required String ssid,
    required String password,
  }) async {
    final char = _require(charMap, 'prov-config');
    final payload = NetworkConfigPayload(
      msg: NetworkConfigMsgType.TypeCmdSetWifiConfig,
      cmdSetWifiConfig: CmdSetWifiConfig(
        ssid: utf8.encode(ssid),
        passphrase: utf8.encode(password),
      ),
    );
    final respBytes = await _writeRead(char, payload.writeToBuffer());
    final resp = NetworkConfigPayload.fromBuffer(respBytes);
    if (resp.respSetWifiConfig.status != Status.Success) {
      throw Exception(
          'Set WiFi config failed: ${resp.respSetWifiConfig.status}');
    }
  }

  Future<void> _applyWifiConfig(
      Map<String, BluetoothCharacteristic> charMap) async {
    final char = _require(charMap, 'prov-config');
    final payload = NetworkConfigPayload(
      msg: NetworkConfigMsgType.TypeCmdApplyWifiConfig,
      cmdApplyWifiConfig: CmdApplyWifiConfig(),
    );
    final respBytes = await _writeRead(char, payload.writeToBuffer());
    final resp = NetworkConfigPayload.fromBuffer(respBytes);
    if (resp.respApplyWifiConfig.status != Status.Success) {
      throw Exception(
          'Apply WiFi config failed: ${resp.respApplyWifiConfig.status}');
    }
  }

  Future<void> _sendMqttConfig(
    Map<String, BluetoothCharacteristic> charMap, {
    required String host,
    required int port,
  }) async {
    final char = _require(charMap, 'custom-mqtt-config');
    final json = '{"host":"$host","port":$port}';
    await _writeRead(char, utf8.encode(json));
  }

  // ---------------------------------------------------------------------------
  // Utilities
  // ---------------------------------------------------------------------------

  Future<List<int>> _writeRead(
      BluetoothCharacteristic char, List<int> data) async {
    await char.write(data, withoutResponse: false);
    return char.read();
  }

  BluetoothCharacteristic _require(
      Map<String, BluetoothCharacteristic> charMap, String name) {
    final char = charMap[name];
    if (char == null) throw Exception('BLE endpoint "$name" not found');
    return char;
  }

  Future<void> _requestScanPermissions() async {
    final statuses = await [
      Permission.bluetoothScan,
      Permission.bluetoothConnect,
      Permission.locationWhenInUse,
    ].request();

    // Only BLE-specific permissions are required on API 31+ where BLUETOOTH_SCAN
    // is declared neverForLocation. On API 31+, ACCESS_FINE_LOCATION is absent from
    // the manifest and auto-denied without prompting, so location denial is not fatal.
    if ([Permission.bluetoothScan, Permission.bluetoothConnect]
        .any((p) => statuses[p]?.isDenied == true || statuses[p]?.isPermanentlyDenied == true)) {
      throw Exception('BLE permissions denied');
    }
  }

  Future<void> _requestConnectPermissions() async {
    final status = await Permission.bluetoothConnect.request();
    if (status.isDenied || status.isPermanentlyDenied) {
      throw Exception('Bluetooth connect permission denied');
    }
  }
}