space-game/apps/backend/Simulation/ScenarioLoader.Spatial.cs

using SpaceGame.Simulation.Api.Data;

namespace SpaceGame.Simulation.Api.Simulation;

public sealed partial class ScenarioLoader
{
  private static SystemSpatialGraph BuildSystemSpatialGraph(SystemRuntime system)
  {
    var nodes = new List<NodeRuntime>();
    var bubbles = new List<LocalBubbleRuntime>();
    var lagrangeNodesByPlanetIndex = new Dictionary<int, Dictionary<string, NodeRuntime>>();

    var starNode = AddSpatialNode(
      nodes,
      bubbles,
      id: $"node-{system.Definition.Id}-star",
      systemId: system.Definition.Id,
      kind: SpatialNodeKind.Star,
      position: Vector3.Zero,
      radius: MathF.Max(system.Definition.GravityWellRadius + StarBubbleRadiusPadding, 180f));

    for (var planetIndex = 0; planetIndex < system.Definition.Planets.Count; planetIndex += 1)
    {
      var planet = system.Definition.Planets[planetIndex];
      var planetNodeId = $"node-{system.Definition.Id}-planet-{planetIndex + 1}";
      var planetPosition = ComputePlanetPosition(planet);
      var planetNode = AddSpatialNode(
        nodes,
        bubbles,
        id: planetNodeId,
        systemId: system.Definition.Id,
        kind: SpatialNodeKind.Planet,
        position: planetPosition,
        radius: MathF.Max(planet.Size + PlanetBubbleRadiusPadding, 120f),
        parentNodeId: starNode.Id);

      var lagrangeNodes = new Dictionary<string, NodeRuntime>(StringComparer.Ordinal);
      foreach (var point in EnumeratePlanetLagrangePoints(planetPosition, planet))
      {
        var lagrangeNode = AddSpatialNode(
          nodes,
          bubbles,
          id: $"node-{system.Definition.Id}-planet-{planetIndex + 1}-{point.Designation.ToLowerInvariant()}",
          systemId: system.Definition.Id,
          kind: SpatialNodeKind.LagrangePoint,
          position: point.Position,
          radius: LagrangeBubbleRadius,
          parentNodeId: planetNode.Id,
          orbitReferenceId: point.Designation);
        lagrangeNodes[point.Designation] = lagrangeNode;
      }

      lagrangeNodesByPlanetIndex[planetIndex] = lagrangeNodes;

      if (planet.MoonCount <= 0)
      {
        continue;
      }

      var moonOrbitRadius = MathF.Max(planet.Size + 48f, 42f);
      for (var moonIndex = 0; moonIndex < planet.MoonCount; moonIndex += 1)
      {
        var moonPosition = ComputeMoonPosition(planetPosition, moonOrbitRadius, moonIndex, planetIndex);
        AddSpatialNode(
          nodes,
          bubbles,
          id: $"node-{system.Definition.Id}-planet-{planetIndex + 1}-moon-{moonIndex + 1}",
          systemId: system.Definition.Id,
          kind: SpatialNodeKind.Moon,
          position: moonPosition,
          radius: MoonBubbleRadiusPadding + 24f,
          parentNodeId: planetNode.Id);
        moonOrbitRadius += 30f;
      }
    }

    return new SystemSpatialGraph(system.Definition.Id, nodes, bubbles, lagrangeNodesByPlanetIndex);
  }

  private static NodeRuntime AddSpatialNode(
    ICollection<NodeRuntime> nodes,
    ICollection<LocalBubbleRuntime> bubbles,
    string id,
    string systemId,
    SpatialNodeKind kind,
    Vector3 position,
    float radius,
    string? parentNodeId = null,
    string? orbitReferenceId = null)
  {
    var bubbleId = $"bubble-{id}";
    var node = new NodeRuntime
    {
      Id = id,
      SystemId = systemId,
      Kind = kind,
      Position = position,
      BubbleId = bubbleId,
      ParentNodeId = parentNodeId,
      OrbitReferenceId = orbitReferenceId,
    };

    nodes.Add(node);
    bubbles.Add(new LocalBubbleRuntime
    {
      Id = bubbleId,
      NodeId = id,
      SystemId = systemId,
      Radius = radius,
    });
    return node;
  }

  private static IEnumerable<LagrangePointPlacement> EnumeratePlanetLagrangePoints(
    Vector3 planetPosition,
    PlanetDefinition planet)
  {
    var radial = NormalizeOrFallback(planetPosition, new Vector3(1f, 0f, 0f));
    var tangential = new Vector3(-radial.Z, 0f, radial.X);
    var orbitRadiusKm = MathF.Sqrt(planetPosition.X * planetPosition.X + planetPosition.Z * planetPosition.Z);
    var offset = ComputePlanetLocalLagrangeOffset(orbitRadiusKm, planet);
    var triangularAngle = MathF.PI / 3f;

    yield return new LagrangePointPlacement("L1", Add(planetPosition, Scale(radial, -offset)));
    yield return new LagrangePointPlacement("L2", Add(planetPosition, Scale(radial, offset)));
    yield return new LagrangePointPlacement("L3", Scale(radial, -orbitRadiusKm));
    yield return new LagrangePointPlacement(
      "L4",
      Add(
        Scale(radial, orbitRadiusKm * MathF.Cos(triangularAngle)),
        Scale(tangential, orbitRadiusKm * MathF.Sin(triangularAngle))));
    yield return new LagrangePointPlacement(
      "L5",
      Add(
        Scale(radial, orbitRadiusKm * MathF.Cos(triangularAngle)),
        Scale(tangential, -orbitRadiusKm * MathF.Sin(triangularAngle))));
  }

  private static float ComputePlanetLocalLagrangeOffset(float orbitRadiusKm, PlanetDefinition planet)
  {
    var planetMassProxy = EstimatePlanetMassRatio(planet);
    var hillLikeOffset = orbitRadiusKm * MathF.Cbrt(MathF.Max(planetMassProxy / 3f, 1e-9f));
    var minimumOffset = MathF.Max(planet.Size * 4f, 25000f);
    return MathF.Max(minimumOffset, hillLikeOffset);
  }

  // The simulation does not track physical masses yet, so use a size/density proxy.
  private static float EstimatePlanetMassRatio(PlanetDefinition planet)
  {
    var earthRadiusRatio = MathF.Max(planet.Size / 6371f, 0.05f);
    var densityFactor = planet.PlanetType switch
    {
      "gas-giant" => 0.24f,
      "ice-giant" => 0.18f,
      "oceanic" => 0.95f,
      "ice" => 0.7f,
      _ => 1f,
    };

    var earthMasses = MathF.Pow(earthRadiusRatio, 3f) * densityFactor;
    return earthMasses / 332_946f;
  }

  private static StationPlacement ResolveStationPlacement(
    InitialStationDefinition plan,
    SystemRuntime system,
    SystemSpatialGraph graph,
    IReadOnlyCollection<NodeRuntime> existingNodes)
  {
    if (plan.PlanetIndex is int planetIndex &&
        graph.LagrangeNodesByPlanetIndex.TryGetValue(planetIndex, out var lagrangeNodes))
    {
      var designation = ResolveLagrangeDesignation(plan.LagrangeSide);
      if (lagrangeNodes.TryGetValue(designation, out var lagrangeNode))
      {
        return new StationPlacement(lagrangeNode, lagrangeNode.Position);
      }
    }

    if (plan.Position is { Length: 3 })
    {
      var targetPosition = NormalizeScenarioPoint(system, plan.Position);
      var preferredNode = existingNodes
        .Where((node) => node.SystemId == system.Definition.Id && node.Kind == SpatialNodeKind.LagrangePoint)
        .OrderBy((node) => node.Position.DistanceTo(targetPosition))
        .FirstOrDefault()
        ?? existingNodes
          .Where((node) => node.SystemId == system.Definition.Id)
          .OrderBy((node) => node.Position.DistanceTo(targetPosition))
          .First();
      return new StationPlacement(preferredNode, preferredNode.Position);
    }

    var fallbackNode = graph.Nodes
      .FirstOrDefault((node) => node.Kind == SpatialNodeKind.LagrangePoint && string.IsNullOrEmpty(node.OccupyingStructureId))
      ?? graph.Nodes.First((node) => node.Kind == SpatialNodeKind.Planet);
    return new StationPlacement(fallbackNode, fallbackNode.Position);
  }

  private static string ResolveLagrangeDesignation(int? lagrangeSide) => lagrangeSide switch
  {
    < 0 => "L4",
    > 0 => "L5",
    _ => "L1",
  };

  private static NodeRuntime? ResolveResourceNodeAnchor(SystemSpatialGraph graph, ResourceNodeDefinition definition)
  {
    if (definition.AnchorPlanetIndex is not int planetIndex || planetIndex < 0)
    {
      return null;
    }

    if (definition.AnchorMoonIndex is int moonIndex && moonIndex >= 0)
    {
      var moonNodeId = $"node-{graph.SystemId}-planet-{planetIndex + 1}-moon-{moonIndex + 1}";
      return graph.Nodes.FirstOrDefault((node) => node.Id == moonNodeId);
    }

    var planetNodeId = $"node-{graph.SystemId}-planet-{planetIndex + 1}";
    return graph.Nodes.FirstOrDefault((node) => node.Id == planetNodeId);
  }

  private static Vector3 ComputeResourceNodePosition(NodeRuntime? anchorNode, ResourceNodeDefinition definition, float yPlane)
  {
    var verticalOffset = MathF.Sin(DegreesToRadians(definition.InclinationDegrees)) * MathF.Min(definition.RadiusOffset * 0.04f, 25000f);
    var offset = new Vector3(
      MathF.Cos(definition.Angle) * definition.RadiusOffset,
      verticalOffset,
      MathF.Sin(definition.Angle) * definition.RadiusOffset);

    if (anchorNode is null)
    {
      return new Vector3(offset.X, yPlane + offset.Y, offset.Z);
    }

    return Add(anchorNode.Position, offset);
  }

  private static Vector3 ComputePlanetPosition(PlanetDefinition planet)
  {
    var angle = DegreesToRadians(planet.OrbitPhaseAtEpoch);
    var orbitRadiusKm = SimulationUnits.AuToKilometers(planet.OrbitRadius);
    var x = MathF.Cos(angle) * orbitRadiusKm;
    var z = MathF.Sin(angle) * orbitRadiusKm;
    return new Vector3(x, 0f, z);
  }

  private static Vector3 ComputeMoonPosition(Vector3 planetPosition, float orbitRadius, int moonIndex, int planetIndex)
  {
    var angle = ((MathF.PI * 2f) / MathF.Max(1, moonIndex + 3)) * (moonIndex + 1) + (planetIndex * 0.37f);
    return Add(planetPosition, new Vector3(MathF.Cos(angle) * orbitRadius, 0f, MathF.Sin(angle) * orbitRadius));
  }

  private static ShipSpatialStateRuntime CreateInitialShipSpatialState(string systemId, Vector3 position, IReadOnlyCollection<NodeRuntime> nodes)
  {
    var nearestNode = nodes
      .Where((node) => node.SystemId == systemId)
      .OrderBy((node) => node.Position.DistanceTo(position))
      .FirstOrDefault();

    return new ShipSpatialStateRuntime
    {
      CurrentSystemId = systemId,
      SpaceLayer = SpaceLayerKinds.LocalSpace,
      CurrentNodeId = nearestNode?.Id,
      CurrentBubbleId = nearestNode?.BubbleId,
      LocalPosition = position,
      SystemPosition = position,
      MovementRegime = MovementRegimeKinds.LocalFlight,
    };
  }

  private sealed record SystemSpatialGraph(
    string SystemId,
    List<NodeRuntime> Nodes,
    List<LocalBubbleRuntime> Bubbles,
    Dictionary<int, Dictionary<string, NodeRuntime>> LagrangeNodesByPlanetIndex);

  private sealed record LagrangePointPlacement(string Designation, Vector3 Position);

  private sealed record StationPlacement(NodeRuntime AnchorNode, Vector3 Position);
}