maps-saas/packages/tactical_app/lib/services/viewshed_360_engine.dart

import 'dart:math' as math;
import 'package:flutter/foundation.dart';
import 'package:intaleq_maps/intaleq_maps.dart';
import 'offline_los_engine.dart';
import 'dem_tile_elevation_service.dart';

/// One radial sight ray from observer at a specific azimuth angle
class RadialRayResult {
  final double azimuthDeg;
  final double maxRangeMeters;
  final double visibleDistanceMeters;
  final LatLng endpoint;
  final bool isBlockedByTerrain;
  final LatLng? obstacleCoord;
  final double? obstacleElevation;

  const RadialRayResult({
    required this.azimuthDeg,
    required this.maxRangeMeters,
    required this.visibleDistanceMeters,
    required this.endpoint,
    required this.isBlockedByTerrain,
    this.obstacleCoord,
    this.obstacleElevation,
  });
}

/// 360° Comprehensive Tactical Viewshed (حقل الرؤية والرصد الدائري 360 درجة)
class Viewshed360Report {
  final LatLng center;
  final double observerHeightM;
  final double radiusMeters;
  final double observerGroundElevM;
  final double observerTotalElevM;
  final List<RadialRayResult> rays;
  final List<LatLng> polygonVertices;
  final double visibleAreaSqKm;
  final double totalPotentialAreaSqKm;
  final int visibilityPercentage;
  final double averageSightRangeKm;

  const Viewshed360Report({
    required this.center,
    required this.observerHeightM,
    required this.radiusMeters,
    required this.observerGroundElevM,
    required this.observerTotalElevM,
    required this.rays,
    required this.polygonVertices,
    required this.visibleAreaSqKm,
    required this.totalPotentialAreaSqKm,
    required this.visibilityPercentage,
    required this.averageSightRangeKm,
  });

  void printTelemetry() {
    debugPrint(
        '════════════════════════════════════════════════════════════════════');
    debugPrint('🌐 [TACTICAL 360° VIEWSHED & FAN COVERAGE REPORT]');
    debugPrint(
        '• مركز الرصد: ${center.latitude.toStringAsFixed(5)}, ${center.longitude.toStringAsFixed(5)}');
    debugPrint(
        '• ارتفاع سطح الأرض: ${observerGroundElevM.round()}م | إجمالي مع البصريات: ${observerTotalElevM.round()}م');
    debugPrint(
        '• نصف قطر المسح: ${(radiusMeters / 1000.0).toStringAsFixed(1)} كم');
    debugPrint('• عدد أشعة المسح: ${rays.length} شعاع (360° Radial Sweep)');
    debugPrint(
        '• مساحة الرؤية المكشوفة: ${visibleAreaSqKm.toStringAsFixed(2)} كم² من أصل ${totalPotentialAreaSqKm.toStringAsFixed(2)} كم²');
    debugPrint('• كفاءة التغطية البصرية: $visibilityPercentage%');
    debugPrint(
        '• متوسط مدى الرؤية الفعلي: ${averageSightRangeKm.toStringAsFixed(2)} كم');
    debugPrint(
        '════════════════════════════════════════════════════════════════════');
  }
}

/// Sovereign Ultra-Fast 360° Tactical Viewshed Engine

class Viewshed360Engine {
  Viewshed360Engine._();

  /// Calculate 360° Viewshed asynchronously after pre-fetching real satellite DEM tiles
  static Future<Viewshed360Report> calculateAsync({
    required LatLng observer,
    double radiusMeters = 5000.0,
    double observerHeightM = 2.0,
    double targetHeightM = 1.5,
    int rayCount = 120,
    int samplesPerRay = 30,
  }) async {
    final dLat = (radiusMeters / 111132.95);
    final dLng = (radiusMeters /
        (111412.84 * math.cos(observer.latitude * math.pi / 180.0)));
    final boundingCoords = [
      LatLng(observer.latitude + dLat, observer.longitude + dLng),
      LatLng(observer.latitude - dLat, observer.longitude + dLng),
      LatLng(observer.latitude + dLat, observer.longitude - dLng),
      LatLng(observer.latitude - dLat, observer.longitude - dLng),
    ];
    await DemTileElevationService.prefetchTilesForCoords(boundingCoords,
        zoom: 12);
    return calculate(
      observer: observer,
      radiusMeters: radiusMeters,
      observerHeightM: observerHeightM,
      targetHeightM: targetHeightM,
      rayCount: rayCount,
      samplesPerRay: samplesPerRay,
    );
  }

  /// Calculate 360° Viewshed in real-time on device (Takes 10-30ms)
  static Viewshed360Report calculate({
    required LatLng observer,
    double radiusMeters = 5000.0,
    double observerHeightM = 2.0,
    double targetHeightM = 1.5,
    int rayCount =
        120, // 1 ray every 3 degrees (120 rays) or 360 rays for maximum density
    int samplesPerRay = 30,
  }) {
    final obsGround = DemTileElevationService.getElevationSync(
        observer.latitude, observer.longitude);
    final obsTotal = obsGround + observerHeightM;

    final rays = <RadialRayResult>[];
    final polygon = <LatLng>[];
    double sumDist = 0.0;
    double visibleAreaAccumulator = 0.0;

    final degStep = 360.0 / rayCount;
    final latRad = observer.latitude * (math.pi / 180.0);
    const earthMetersPerLatDeg = 111132.95;
    final earthMetersPerLngDeg = 111412.84 * math.cos(latRad);

    const int samples = 30;

    for (int i = 0; i < rayCount; i++) {
      final azDeg = i * degStep;
      final azRad = azDeg * (math.pi / 180.0);

      final dLat = (radiusMeters * math.cos(azRad)) / earthMetersPerLatDeg;
      final dLng = (radiusMeters * math.sin(azRad)) / earthMetersPerLngDeg;

      double maxAngleSoFar = -double.infinity;
      double visibleHorizonDist = radiusMeters;
      double visibleHorizonLat = observer.latitude + dLat;
      double visibleHorizonLng = observer.longitude + dLng;
      bool isBlocked = false;
      LatLng? blockCoord;
      double? blockElev;

      for (int step = 1; step <= samples; step++) {
        final frac = step / samples;
        final sDist = radiusMeters * frac;
        final sLat = observer.latitude + dLat * frac;
        final sLng = observer.longitude + dLng * frac;

        final sElev = DemTileElevationService.getElevationSync(sLat, sLng);
        final sagitta = JordanDemSurface.sagitta(sDist, radiusMeters - sDist);
        final apparentElev = sElev + targetHeightM - sagitta;
        final angle = (apparentElev - obsTotal) / sDist;

        if (angle >= maxAngleSoFar) {
          maxAngleSoFar = angle;
          visibleHorizonDist = sDist;
          visibleHorizonLat = sLat;
          visibleHorizonLng = sLng;
        } else {
          if (!isBlocked) {
            isBlocked = true;
            blockCoord = LatLng(sLat, sLng);
            blockElev = sElev;
          }
        }
      }

      final endPoint = LatLng(visibleHorizonLat, visibleHorizonLng);

      rays.add(RadialRayResult(
        azimuthDeg: azDeg,
        maxRangeMeters: radiusMeters,
        visibleDistanceMeters: visibleHorizonDist,
        endpoint: endPoint,
        isBlockedByTerrain: isBlocked,
        obstacleCoord: blockCoord,
        obstacleElevation: blockElev,
      ));

      polygon.add(endPoint);
      sumDist += visibleHorizonDist;

      // Sector area accumulation = 0.5 * r^2 * dTheta
      final dThetaRad = degStep * (math.pi / 180.0);
      visibleAreaAccumulator += 0.5 *
          (visibleHorizonDist / 1000.0) *
          (visibleHorizonDist / 1000.0) *
          dThetaRad;
    }

    if (polygon.isNotEmpty) {
      polygon.add(polygon.first); // Close the polygon ring
    }

    final totalPotentialArea =
        math.pi * (radiusMeters / 1000.0) * (radiusMeters / 1000.0);
    final visPercent = totalPotentialArea > 0
        ? ((visibleAreaAccumulator / totalPotentialArea) * 100)
            .round()
            .clamp(0, 100)
        : 0;
    final avgRange = rayCount > 0 ? (sumDist / rayCount) / 1000.0 : 0.0;

    final report = Viewshed360Report(
      center: observer,
      observerHeightM: observerHeightM,
      radiusMeters: radiusMeters,
      observerGroundElevM: obsGround,
      observerTotalElevM: obsTotal,
      rays: rays,
      polygonVertices: polygon,
      visibleAreaSqKm: visibleAreaAccumulator,
      totalPotentialAreaSqKm: totalPotentialArea,
      visibilityPercentage: visPercent,
      averageSightRangeKm: avgRange,
    );

    report.printTelemetry();
    return report;
  }
}