// Copyright IHY.
#pragma once

#include "CoreMinimal.h"

class UStaticMesh;

/**
 * Rotation/translation-invariant geometry fingerprint of a single UStaticMesh, plus the
 * (lazily loaded) welded vertex cloud used for exact pairwise verification.
 *
 * Source is always LOD0 FMeshDescription (the imported authoring geometry) so the fingerprint
 * is stable across LOD reduction / Nanite / build settings. Render data is a tagged fallback.
 */
struct FOptMeshGeom
{
	static constexpr int32 NumRadialBins = 16;

	bool bValid = false;
	bool bRenderDerived = false;   // true if extracted from render data (compare only against other render-derived)

	int32 RawVertexCount = 0;
	int32 WeldedVertexCount = 0;   // unique positions after welding -> the hard fingerprint gate
	int32 TriangleCount = 0;

	double SurfaceArea = 0.0;      // local space, rigid-invariant, scales as s^2
	double Volume = 0.0;           // |signed tetrahedron sum|, scales as s^3
	FVector Centroid = FVector::ZeroVector;            // mean of welded positions (local origin for cov/hist)
	double EigenValues[3] = { 0.0, 0.0, 0.0 };         // covariance eigenvalues, sorted DESC (rotation-invariant)
	double RadialHistogram[NumRadialBins] = { 0.0 };   // normalized hist of |v - centroid|
	FBox LocalBounds = FBox(ForceInit);

	// Heavy payload, populated only when this mesh enters pairwise recovery (bWantPositions).
	TArray<FVector> Positions;     // welded unique positions, local space

	// Material / section signature (NOT part of geometry grouping; used to partition for HISM).
	uint32 MaterialHash = 0;
	int32 SectionCount = 0;
};

namespace OptimizerGeometry
{
	/**
	 * Extract the fingerprint (and optionally the welded position cloud) for a static mesh.
	 * @param WeldEps   position weld grid in cm.
	 * @param bWantPositions  also fill Out.Positions (the expensive part) for verification.
	 * @return false if no usable geometry could be read.
	 */
	bool ExtractGeom(const UStaticMesh* Mesh, float WeldEps, bool bWantPositions, FOptMeshGeom& Out);

	/** Symmetric 3x3 Jacobi eigensolver. Eigenvalues returned sorted DESC; eigenvectors as columns of OutVecs. */
	void SymmetricEigen3x3(const double M[3][3], double OutValues[3], double OutVecs[3][3]);
}