import 'dart:convert';
import 'dart:math' as math;

import 'package:http/http.dart' as http;
import 'package:latlong2/latlong.dart';

class BusStop {
  const BusStop({
    required this.id,
    required this.name,
    required this.position,
    this.stopLetter,
    this.towards,
  });

  final String id;
  final String name;
  final LatLng position;

  // the letter on the physical bus stop flag e.g. "A", "ZH"
  final String? stopLetter;

  // may be null for parent stops
  final String? towards;
}

class TflBusStopService {
  TflBusStopService();

  static const _baseUrl = 'https://api.tfl.gov.uk';

  // max radius the TfL API accepts is 1600m but in practice
  // we clamp to 800 so we dont get swamped at low zoom
  static const _maxRadius = 800;

  Future<List<BusStop>> fetchNearby(LatLng center, {int radius = 600}) async {
    final r = radius.clamp(0, _maxRadius);

    final uri = Uri.parse(
      '$_baseUrl/StopPoint'
      '?stopTypes=NaptanPublicBusCoachTram'
      '&lat=${center.latitude}'
      '&lon=${center.longitude}'
      '&radius=$r'
      '&modes=bus',
    );

    final response = await http.get(uri, headers: {
      'Accept': 'application/json',
    });

    if (response.statusCode != 200) {
      throw Exception('TfL StopPoint request failed (${response.statusCode})');
    }

    final body = jsonDecode(response.body) as Map<String, dynamic>;
    final stopPoints = body['stopPoints'];
    if (stopPoints is! List) return const [];

    final stops = <BusStop>[];
    for (final raw in stopPoints) {
      if (raw is! Map<String, dynamic>) continue;

      final lat = (raw['lat'] as num?)?.toDouble();
      final lon = (raw['lon'] as num?)?.toDouble();
      if (lat == null || lon == null) continue;

      final id = raw['id'] as String? ?? '';
      final name = raw['commonName'] as String? ?? '';
      final stopLetter = raw['stopLetter'] as String?;

      String? towards;
      final addInfo = raw['additionalProperties'];
      if (addInfo is List) {
        for (final prop in addInfo) {
          if (prop is Map && prop['key'] == 'Towards') {
            towards = prop['value'] as String?;
            break;
          }
        }
      }

      stops.add(BusStop(
        id: id,
        name: name,
        position: LatLng(lat, lon),
        stopLetter: stopLetter,
        towards: towards,
      ));
    }

    return stops;
  }

  // rough haversine distance in metres, good enough for radius estimation
  static double metersPerPixel(double lat, double zoom) {
    const earthCircumference = 40075016.686;
    final latRad = lat * math.pi / 180.0;
    return (earthCircumference * math.cos(latRad)) /
        (256 * math.pow(2, zoom));
  }
}