import 'dart:async';
import 'package:flutter/material.dart';
import 'package:dchs_flutter_beacon/dchs_flutter_beacon.dart';
import 'package:provider/provider.dart';

import '../app/app_router.dart';
import '../app/app_state.dart';
import '../services/beacon_permissions.dart';
import '../services/api.dart';

class BeaconScanScreen extends StatefulWidget {
  const BeaconScanScreen({super.key});

  @override
  State<BeaconScanScreen> createState() => _BeaconScanScreenState();
}

class _BeaconScanScreenState extends State<BeaconScanScreen> with SingleTickerProviderStateMixin {
  String _status = 'Initializing...';
  bool _permissionsGranted = false;
  bool _scanning = false;

  Map<String, int> _uuidToBeaconId = {};
  final Map<String, List<int>> _beaconRssiSamples = {}; // UUID -> List of RSSI values
  final Map<String, int> _beaconDetectionCount = {}; // UUID -> detection count

  // Rotating scan messages
  static const List<String> _scanMessages = [
    'Looking for your table...',
    'Scanning nearby...',
    'Almost there...',
    'Checking signal strength...',
    'Finalizing...',
  ];

  late AnimationController _pulseController;
  late Animation<double> _pulseAnimation;

  @override
  void initState() {
    super.initState();
    _pulseController = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 1500),
    )..repeat(reverse: true);
    _pulseAnimation = Tween<double>(begin: 0.8, end: 1.2).animate(
      CurvedAnimation(parent: _pulseController, curve: Curves.easeInOut),
    );
    _startScanFlow();
  }

  @override
  void dispose() {
    _pulseController.dispose();
    super.dispose();
  }

  Future<void> _startScanFlow() async {
    // Step 1: Request permissions
    setState(() => _status = 'Requesting permissions...');

    final granted = await BeaconPermissions.requestPermissions();

    if (!granted) {
      setState(() {
        _status = 'Permissions denied - Please enable Location & Bluetooth';
        _permissionsGranted = false;
      });
      return;
    }

    setState(() => _permissionsGranted = true);

    // Step 1.5: Check if Bluetooth is ON
    setState(() => _status = 'Checking Bluetooth...');

    final bluetoothOn = await BeaconPermissions.ensureBluetoothEnabled();

    if (!bluetoothOn) {
      setState(() {
        _status = 'Please turn on Bluetooth to scan for tables';
        _scanning = false;
      });
      // Wait and retry, or let user manually proceed
      await Future.delayed(const Duration(seconds: 2));
      if (mounted) _navigateToRestaurantSelect();
      return;
    }

    // Step 2: Fetch all active beacons from server
    setState(() => _status = 'Loading beacon data...');

    try {
      _uuidToBeaconId = await Api.listAllBeacons();
    } catch (e) {
      _uuidToBeaconId = {};
    }

    if (_uuidToBeaconId.isEmpty) {
      if (mounted) _navigateToRestaurantSelect();
      return;
    }

    // Step 3: Perform initial scan
    setState(() {
      _status = 'Scanning for nearby beacons...';
      _scanning = true;
    });

    await _performInitialScan();
  }

  Future<void> _performInitialScan() async {
    try {
      // Initialize beacon monitoring
      await flutterBeacon.initializeScanning;

      // Brief delay to let Bluetooth subsystem fully initialize
      await Future.delayed(const Duration(milliseconds: 1500));

      // Create regions for all known UUIDs
      final regions = _uuidToBeaconId.keys.map((uuid) {
        // Format UUID with dashes for the plugin
        final formattedUUID = '${uuid.substring(0, 8)}-${uuid.substring(8, 12)}-${uuid.substring(12, 16)}-${uuid.substring(16, 20)}-${uuid.substring(20)}';
        return Region(identifier: uuid, proximityUUID: formattedUUID);
      }).toList();

      if (regions.isEmpty) {
        if (mounted) _navigateToRestaurantSelect();
        return;
      }

      // Perform scan cycles
      for (int scanCycle = 1; scanCycle <= 3; scanCycle++) {
        if (mounted) {
          setState(() => _status = _scanMessages[scanCycle - 1]);
        }

        StreamSubscription<RangingResult>? subscription;

        subscription = flutterBeacon.ranging(regions).listen((result) {
          for (var beacon in result.beacons) {
            final rawUUID = beacon.proximityUUID;
            final uuid = rawUUID.toUpperCase().replaceAll('-', '');
            final rssi = beacon.rssi;

            if (_uuidToBeaconId.containsKey(uuid)) {
              _beaconRssiSamples.putIfAbsent(uuid, () => []).add(rssi);
              _beaconDetectionCount[uuid] = (_beaconDetectionCount[uuid] ?? 0) + 1;
            }
          }
        });

        await Future.delayed(const Duration(milliseconds: 2000));
        await subscription.cancel();

        if (scanCycle < 3) {
          await Future.delayed(const Duration(milliseconds: 500));
        }
      }

      if (!mounted) return;

      // Analyze results and select best beacon
      final beaconScores = <String, BeaconScore>{};

      for (final uuid in _beaconRssiSamples.keys) {
        final samples = _beaconRssiSamples[uuid]!;
        final detections = _beaconDetectionCount[uuid]!;
        final beaconId = _uuidToBeaconId[uuid]!;

        final avgRssi = samples.reduce((a, b) => a + b) / samples.length;
        final variance = samples.map((r) => (r - avgRssi) * (r - avgRssi)).reduce((a, b) => a + b) / samples.length;

        beaconScores[uuid] = BeaconScore(
          uuid: uuid,
          beaconId: beaconId,
          avgRssi: avgRssi,
          minRssi: samples.reduce((a, b) => a < b ? a : b),
          maxRssi: samples.reduce((a, b) => a > b ? a : b),
          detectionCount: detections,
          variance: variance,
        );
      }

      if (beaconScores.isEmpty) {
        setState(() {
          _scanning = false;
          _status = 'No nearby tables detected';
        });
        await Future.delayed(const Duration(milliseconds: 500));
        if (mounted) _navigateToRestaurantSelect();
        return;
      } else {
        final best = _findBestBeacon(beaconScores);
        if (best != null) {
          setState(() => _status = 'Beacon detected! Loading business...');
          await _autoSelectBusinessFromBeacon(best.beaconId);
        } else {
          setState(() {
            _scanning = false;
            _status = 'No strong beacon signal';
          });
          await Future.delayed(const Duration(milliseconds: 500));
          if (mounted) _navigateToRestaurantSelect();
        }
      }
    } catch (e) {
      if (mounted) {
        setState(() {
          _scanning = false;
          _status = 'Scan error - continuing to manual selection';
        });
        await Future.delayed(const Duration(milliseconds: 500));
        if (mounted) _navigateToRestaurantSelect();
      }
    }
  }

  Future<void> _autoSelectBusinessFromBeacon(int beaconId) async {
    try {
      final mapping = await Api.getBusinessFromBeacon(beaconId: beaconId);

      if (!mounted) return;

      // Update app state with selected business and service point
      final appState = context.read<AppState>();
      appState.setBusinessAndServicePoint(
        mapping.businessId,
        mapping.servicePointId,
        businessName: mapping.businessName,
        servicePointName: mapping.servicePointName,
      );

      // Set order type to dine-in since beacon was detected
      appState.setOrderType(OrderType.dineIn);

      // Update API business ID for headers
      Api.setBusinessId(mapping.businessId);

      setState(() => _status = 'Welcome to ${mapping.businessName}!');
      await Future.delayed(const Duration(milliseconds: 800));

      if (!mounted) return;

      // Navigate directly to menu (user can browse without logging in)
      Navigator.of(context).pushReplacementNamed(
        AppRoutes.menuBrowse,
        arguments: {
          'businessId': mapping.businessId,
          'servicePointId': mapping.servicePointId,
        },
      );
    } catch (e) {
      debugPrint('[BeaconScan] Error fetching business from beacon: $e');
      if (mounted) {
        setState(() => _status = 'Beacon not assigned - selecting manually');
        await Future.delayed(const Duration(seconds: 1));
        if (mounted) _navigateToRestaurantSelect();
      }
    }
  }

  /// Check if we can exit early based on stable readings
  /// Returns true if all detected beacons have consistent RSSI across scans
  bool _canExitEarly() {
    if (_beaconRssiSamples.isEmpty) return false;

    // Need at least one beacon with 3+ readings
    bool hasEnoughSamples = _beaconRssiSamples.values.any((samples) => samples.length >= 2);
    if (!hasEnoughSamples) return false;

    // Check if there's a clear winner or if all beacons have low variance
    for (final entry in _beaconRssiSamples.entries) {
      final samples = entry.value;
      if (samples.length < 3) continue;

      final avg = samples.reduce((a, b) => a + b) / samples.length;
      final variance = samples.map((r) => (r - avg) * (r - avg)).reduce((a, b) => a + b) / samples.length;

      // If variance is high, keep scanning
      if (variance > 50) {
        return false;
      }
    }

    // If multiple beacons, check if there's a clear strongest one
    if (_beaconRssiSamples.length > 1) {
      final avgRssis = <String, double>{};
      for (final entry in _beaconRssiSamples.entries) {
        final samples = entry.value;
        if (samples.isNotEmpty) {
          avgRssis[entry.key] = samples.reduce((a, b) => a + b) / samples.length;
        }
      }

      final sorted = avgRssis.entries.toList()..sort((a, b) => b.value.compareTo(a.value));

      // If top two beacons are within 5 dB, keep scanning for more clarity
      if (sorted.length >= 2) {
        final diff = sorted[0].value - sorted[1].value;
        if (diff < 5) {
          return false;
        }
      }
    }

    return true;
  }

  BeaconScore? _findBestBeacon(Map<String, BeaconScore> scores) {
    if (scores.isEmpty) return null;

    // Filter beacons that meet minimum requirements
    const minDetections = 2; // Must be seen at least 3 times
    const minRssi = -85; // Minimum average RSSI (beacons further than ~10m will be weaker)

    final qualified = scores.values.where((score) {
      return score.detectionCount >= minDetections && score.avgRssi >= minRssi;
    }).toList();

    if (qualified.isEmpty) {
      debugPrint('[BeaconScan] No beacons met minimum requirements (detections>=$minDetections, avgRSSI>=$minRssi)');
      // Fall back to best available beacon if none meet threshold
      final allSorted = scores.values.toList()
        ..sort((a, b) => b.avgRssi.compareTo(a.avgRssi));
      return allSorted.isNotEmpty ? allSorted.first : null;
    }

    // Sort by average RSSI (higher is better/closer)
    qualified.sort((a, b) => b.avgRssi.compareTo(a.avgRssi));

    return qualified.first;
  }

  void _navigateToRestaurantSelect() {
    Navigator.of(context).pushReplacementNamed(AppRoutes.restaurantSelect);
  }

  void _retryPermissions() async {
    await BeaconPermissions.openSettings();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            if (_scanning)
              ScaleTransition(
                scale: _pulseAnimation,
                child: Container(
                  width: 100,
                  height: 100,
                  decoration: BoxDecoration(
                    shape: BoxShape.circle,
                    gradient: RadialGradient(
                      colors: [
                        Colors.blue.withAlpha(102),
                        Colors.blue.withAlpha(26),
                      ],
                    ),
                  ),
                  child: const Icon(
                    Icons.bluetooth_searching,
                    color: Colors.white,
                    size: 48,
                  ),
                ),
              )
            else if (_permissionsGranted)
              const Icon(Icons.bluetooth_searching, color: Colors.white70, size: 64)
            else
              const Icon(Icons.bluetooth_disabled, color: Colors.white70, size: 64),

            const SizedBox(height: 24),

            Text(
              _status,
              style: const TextStyle(
                color: Colors.white,
                fontSize: 16,
                fontWeight: FontWeight.w500,
              ),
              textAlign: TextAlign.center,
            ),

            if (_beaconRssiSamples.isNotEmpty) ...[
              const SizedBox(height: 16),
              Text(
                'Found ${_beaconRssiSamples.length} beacon(s)',
                style: const TextStyle(color: Colors.white70, fontSize: 12),
              ),
            ],

            if (!_permissionsGranted && _status.contains('denied')) ...[
              const SizedBox(height: 24),
              FilledButton(
                onPressed: _retryPermissions,
                child: const Text('Open Settings'),
              ),
            ],

            // Always show manual selection option during or after scan
            if (_permissionsGranted) ...[
              const SizedBox(height: 32),
              TextButton(
                onPressed: _navigateToRestaurantSelect,
                child: const Text(
                  'Select Restaurant Manually',
                  style: TextStyle(
                    color: Colors.white70,
                    fontSize: 14,
                  ),
                ),
              ),
            ],
          ],
        ),
      ),
    );
  }
}

class BeaconScore {
  final String uuid;
  final int beaconId;
  final double avgRssi;
  final int minRssi;
  final int maxRssi;
  final int detectionCount;
  final double variance;

  const BeaconScore({
    required this.uuid,
    required this.beaconId,
    required this.avgRssi,
    required this.minRssi,
    required this.maxRssi,
    required this.detectionCount,
    required this.variance,
  });
}