Europa/Nuvolari/app/lib/core/region/geo.dart

import 'dart:math' as math;

/// A point on the globe in degrees.
class GeoPoint {
  const GeoPoint(this.longitude, this.latitude);

  final double longitude;
  final double latitude;

  @override
  String toString() => 'GeoPoint($longitude, $latitude)';

  @override
  bool operator ==(Object other) =>
      other is GeoPoint &&
      other.longitude == longitude &&
      other.latitude == latitude;

  @override
  int get hashCode => Object.hash(longitude, latitude);
}

/// An axis-aligned geographic bounding box in degrees.
///
/// Serialised as `[west, south, east, north]`, the ordering GeoJSON and GDAL
/// both use, so a bbox can be copied between the region config, the worker and
/// the published manifest without being reordered on the way.
class GeoBounds {
  const GeoBounds({
    required this.west,
    required this.south,
    required this.east,
    required this.north,
  });

  /// Parses the `[west, south, east, north]` form.
  ///
  /// Throws [FormatException] if the list is the wrong length, holds
  /// non-numbers, or describes an empty or out-of-range box. An inverted box is
  /// rejected rather than silently normalised: the likely cause is a swapped
  /// latitude and longitude, and normalising would hide it.
  factory GeoBounds.fromJson(Object? json) {
    if (json is! List || json.length != 4) {
      throw const FormatException(
        'bbox must be a list of four numbers [west, south, east, north]',
      );
    }
    final values = <double>[];
    for (final entry in json) {
      if (entry is! num) {
        throw FormatException('bbox contains a non-numeric value: $entry');
      }
      values.add(entry.toDouble());
    }
    final bounds = GeoBounds(
      west: values[0],
      south: values[1],
      east: values[2],
      north: values[3],
    );
    bounds._validate();
    return bounds;
  }

  final double west;
  final double south;
  final double east;
  final double north;

  double get widthDegrees => east - west;
  double get heightDegrees => north - south;

  GeoPoint get center =>
      GeoPoint(west + widthDegrees / 2, south + heightDegrees / 2);

  bool contains(GeoPoint point) =>
      point.longitude >= west &&
      point.longitude <= east &&
      point.latitude >= south &&
      point.latitude <= north;

  void _validate() {
    if (west < -180 || east > 180) {
      throw FormatException('bbox longitude out of range: $west..$east');
    }
    if (south < -90 || north > 90) {
      throw FormatException('bbox latitude out of range: $south..$north');
    }
    if (east <= west) {
      throw FormatException(
        'bbox east ($east) must be greater than west ($west)',
      );
    }
    if (north <= south) {
      throw FormatException(
        'bbox north ($north) must be greater than south ($south)',
      );
    }
  }

  List<double> toJson() => [west, south, east, north];

  @override
  String toString() => 'GeoBounds($west, $south, $east, $north)';

  @override
  bool operator ==(Object other) =>
      other is GeoBounds &&
      other.west == west &&
      other.south == south &&
      other.east == east &&
      other.north == north;

  @override
  int get hashCode => Object.hash(west, south, east, north);
}

/// Web Mercator helpers.
///
/// The worker publishes frames already reprojected to EPSG:3857, so the app
/// only needs the forward transform to reason about frame geometry — never the
/// warp itself.
class WebMercator {
  const WebMercator._();

  /// Latitude beyond which Web Mercator is undefined in practice.
  static const double maxLatitude = 85.05112878;

  static double xFromLongitude(double longitude) => longitude / 360 + 0.5;

  static double yFromLatitude(double latitude) {
    final clamped = latitude.clamp(-maxLatitude, maxLatitude);
    final sin = math.sin(clamped * math.pi / 180);
    return 0.5 - math.log((1 + sin) / (1 - sin)) / (4 * math.pi);
  }
}