/*
 * #%L
 * Image processing operations for SciJava Ops.
 * %%
 * Copyright (C) 2014 - 2024 SciJava developers.
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package org.scijava.ops.image.geom.geom3d;

import java.util.function.Function;

import net.imglib2.mesh.Mesh;
import net.imglib2.mesh.Triangle;
import net.imglib2.type.numeric.real.DoubleType;

import org.apache.commons.math3.util.MathArrays;

/**
 * Generic implementation of {@code geom.size}.
 *
 * @author Tim-Oliver Buchholz (University of Konstanz)
 * @implNote op names='geom.size', label='Geometric (2D): Size',
 *           priority='9999.'
 */
public class DefaultVolumeMesh implements Function<Mesh, DoubleType> {

	/**
	 * TODO
	 *
	 * @param input
	 * @return the volume
	 */
	@Override
	public DoubleType apply(final Mesh input) {
		double volume = 0;
		for (final var triangle : input.triangles()) {
			volume += signedVolumeOfTriangle(//
				triangle.v0x(), triangle.v0y(), triangle.v0z(), //
				triangle.v1x(), triangle.v1y(), triangle.v1z(), //
				triangle.v2x(), triangle.v2y(), triangle.v2z());
		}
		return new DoubleType(Math.abs(volume));
	}

	private double signedVolumeOfTriangle(//
		final double p0x, final double p0y, final double p0z, //
		final double p1x, final double p1y, final double p1z, //
		final double p2x, final double p2y, final double p2z)
	{
		// cross product
		final var cpx = MathArrays.linearCombination(p1y, p2z, -p1z, p2y);
		final var cpy = MathArrays.linearCombination(p1z, p2x, -p1x, p2z);
		final var cpz = MathArrays.linearCombination(p1x, p2y, -p1y, p2x);

		// dot product
		return MathArrays.linearCombination(p0x, cpx, p0y, cpy, p0z, cpz) / 6.0f;
	}
}
