/*
 * #%L
 * Image processing operations for SciJava Ops.
 * %%
 * Copyright (C) 2014 - 2024 SciJava developers.
 * %%
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 *    this list of conditions and the following disclaimer.
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package org.scijava.ops.image.geom.geom2d;

import net.imglib2.RealLocalizable;
import net.imglib2.roi.geom.real.Polygon2D;
import net.imglib2.type.numeric.real.DoubleType;

import org.scijava.function.Computers;

/**
 * Computes the size (i.e. area) of a {@link Polygon2D}.
 *
 * @author Daniel Seebacher (University of Konstanz)
 * @implNote op names='geom.size', label='Geometric (2D): Size', priority =
 *           '9999.'
 */
public class DefaultSizePolygon implements
	Computers.Arity1<Polygon2D, DoubleType>
{

	/**
	 * TODO
	 *
	 * @param input
	 * @param size
	 */
	@Override
	public void compute(Polygon2D input, DoubleType size) {
		double sum = 0;
		final var numVertices = input.numVertices();
		for (var i = 0; i < numVertices; i++) {

			final var p0 = input.vertex(i);
			final var p1 = input.vertex((i + 1) % numVertices);

			final var p0_x = p0.getDoublePosition(0);
			final var p0_y = p0.getDoublePosition(1);
			final var p1_x = p1.getDoublePosition(0);
			final var p1_y = p1.getDoublePosition(1);

			sum += p0_x * p1_y - p0_y * p1_x;
		}
		size.set(Math.abs(sum) / 2d);
	}

}
