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

import 'dart:math' as math;
import 'package:flutter/material.dart';
import 'package:intaleq_maps/intaleq_maps.dart';
import '../models/military_operations_models.dart';
import 'dem_tile_elevation_service.dart';

/// Sovereign On-Device Helicopter Landing Zone (HLZ) Suitability Engine
class HlzAssessmentEngine {
  HlzAssessmentEngine._();

  /// Assess proposed landing site terrain slope, obstacle clearance, and landing corridors
  static Future<HlzAssessmentResult> assessLandingZone({
    required LatLng center,
    required HelicopterType helicopterType,
    double approachAzimuthDeg = 0.0,
  }) async {
    // 1. Determine recommended pad radius based on helicopter airframe size
    double padRadiusM;
    double maxAllowableSlopePct;

    switch (helicopterType) {
      case HelicopterType.lightUtility:
        padRadiusM = 25.0; // 50m diameter
        maxAllowableSlopePct = 15.0; // 15% slope max
        break;
      case HelicopterType.mediumLift:
        padRadiusM = 40.0; // 80m diameter (UH-60 / AH-64)
        maxAllowableSlopePct = 10.0; // 10% slope max
        break;
      case HelicopterType.heavyTransport:
        padRadiusM = 60.0; // 120m diameter (CH-47 Chinook)
        maxAllowableSlopePct = 7.0; // 7% slope max
        break;
    }

    // 2. Query Center Elevation
    final centerElev = await DemTileElevationService.getElevation(center.latitude, center.longitude);

    // 3. Sample 16 cardinal points around the perimeter to calculate maximum terrain slope
    final List<double> perimeterElevs = [];
    final List<LatLng> padBoundary = [];
    const int samplePoints = 16;

    for (int i = 0; i < samplePoints; i++) {
      final angleRad = (i * 2 * math.pi) / samplePoints;
      final dLat = (padRadiusM / 6371000.0) * (180.0 / math.pi) * math.cos(angleRad);
      final dLng = (padRadiusM / (6371000.0 * math.cos(center.latitude * math.pi / 180.0))) * (180.0 / math.pi) * math.sin(angleRad);

      final pLat = center.latitude + dLat;
      final pLng = center.longitude + dLng;
      padBoundary.add(LatLng(pLat, pLng));

      final elev = await DemTileElevationService.getElevation(pLat, pLng);
      perimeterElevs.add(elev);
    }
    // Close polygon
    if (padBoundary.isNotEmpty) padBoundary.add(padBoundary.first);

    // Calculate maximum slope percentage
    double maxSlope = 0.0;
    double slopeSum = 0.0;
    for (final pElev in perimeterElevs) {
      final slopePct = (pElev - centerElev).abs() / padRadiusM * 100.0;
      if (slopePct > maxSlope) maxSlope = slopePct;
      slopeSum += slopePct;
    }
    final avgSlope = slopeSum / perimeterElevs.length;

    // 4. Generate 500m Approach/Departure Funnel
    final List<LatLng> funnel = [];
    const double funnelLengthM = 500.0;
    const double funnelWidthM = 120.0;

    final approachRad = (approachAzimuthDeg * math.pi) / 180.0;
    final perpRad = approachRad + (math.pi / 2);

    // Base point at pad edge
    final baseLat = center.latitude + (padRadiusM / 6371000.0) * (180.0 / math.pi) * math.cos(approachRad);
    final baseLng = center.longitude + (padRadiusM / (6371000.0 * math.cos(center.latitude * math.pi / 180.0))) * (180.0 / math.pi) * math.sin(approachRad);

    // Funnel End Center
    final endCenterLat = center.latitude + (funnelLengthM / 6371000.0) * (180.0 / math.pi) * math.cos(approachRad);
    final endCenterLng = center.longitude + (funnelLengthM / (6371000.0 * math.cos(center.latitude * math.pi / 180.0))) * (180.0 / math.pi) * math.sin(approachRad);

    // Funnel Left & Right
    final leftEndLat = endCenterLat + (funnelWidthM / 2 / 6371000.0) * (180.0 / math.pi) * math.cos(perpRad);
    final leftEndLng = endCenterLng + (funnelWidthM / 2 / (6371000.0 * math.cos(endCenterLat * math.pi / 180.0))) * (180.0 / math.pi) * math.sin(perpRad);

    final rightEndLat = endCenterLat - (funnelWidthM / 2 / 6371000.0) * (180.0 / math.pi) * math.cos(perpRad);
    final rightEndLng = endCenterLng - (funnelWidthM / 2 / (6371000.0 * math.cos(endCenterLat * math.pi / 180.0))) * (180.0 / math.pi) * math.sin(perpRad);

    funnel.addAll([
      LatLng(baseLat, baseLng),
      LatLng(leftEndLat, leftEndLng),
      LatLng(rightEndLat, rightEndLng),
      LatLng(baseLat, baseLng),
    ]);

    // 5. Check Obstacle Height in Funnel
    final endElev = await DemTileElevationService.getElevation(endCenterLat, endCenterLng);
    final funnelRise = endElev - centerElev;
    final isObstacleClear = funnelRise < 35.0; // Less than 35m rise over 500m approach

    // 6. Grade Suitability
    final isSlopeAcceptable = maxSlope <= maxAllowableSlopePct;
    String grade;
    Color gradeColor;

    if (isSlopeAcceptable && maxSlope < (maxAllowableSlopePct * 0.6) && isObstacleClear) {
      grade = 'صالح ومثالي (OPTIMAL GO)';
      gradeColor = const Color(0xFF10B981); // Emerald
    } else if (isSlopeAcceptable && isObstacleClear) {
      grade = 'مقبول بحذر (MARGINAL SLOW-GO)';
      gradeColor = const Color(0xFFF59E0B); // Amber
    } else {
      grade = 'غير صالح للهبوط (UNSUITABLE NO-GO)';
      gradeColor = const Color(0xFFEF4444); // Red
    }

    return HlzAssessmentResult(
      center: center,
      helicopterType: helicopterType,
      groundElevationM: centerElev,
      maxSlopePercent: math.min(100.0, (maxSlope * 10).round() / 10.0),
      avgSlopePercent: (avgSlope * 10).round() / 10.0,
      recommendedClearanceRadiusM: padRadiusM,
      isSlopeAcceptable: isSlopeAcceptable,
      isObstacleClear: isObstacleClear,
      suitabilityGrade: grade,
      gradeColor: gradeColor,
      approachAzimuthDeg: approachAzimuthDeg,
      padBoundary: padBoundary,
      approachFunnel: funnel,
    );
  }
}