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 * Image processing operations for SciJava Ops.
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package org.scijava.ops.image.geom.geom2d;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;

import org.scijava.ops.spi.OpDependency;

import org.scijava.ops.image.geom.GeomUtils;
import net.imglib2.RealLocalizable;
import net.imglib2.RealPoint;
import net.imglib2.roi.geom.real.DefaultWritablePolygon2D;
import net.imglib2.roi.geom.real.Polygon2D;
import net.imglib2.type.numeric.real.DoubleType;

/**
 * Generic implementation of {@code geom.smallestBoundingBox}.
 *
 * @author Daniel Seebacher (University of Konstanz)
 * @implNote op names='geom.smallestEnclosingBoundingBox', label='Geometric
 *           (2D): Smallest Enclosing Rectangle'
 */
public class DefaultSmallestEnclosingRectangle implements
	Function
{

	@OpDependency(name = "geom.convexHull")
	private Function convexHullFunc;
	@OpDependency(name = "geom.centroid")
	private Function centroidFunc;
	@OpDependency(name = "geom.size")
	private Function areaFunc;
	@OpDependency(name = "geom.boundingBox")
	private Function boundingBoxFunc;

	/**
	 * Rotates the given Polygon2D consisting of a list of RealPoints by the given
	 * angle about the given center.
	 *
	 * @param inPoly A Polygon2D consisting of a list of RealPoint RealPoints
	 * @param angle the rotation angle
	 * @param center the rotation center
	 * @return a rotated polygon
	 */
	private Polygon2D rotate(final Polygon2D inPoly, final double angle,
		final RealLocalizable center)
	{

		List out = new ArrayList<>();

		for (RealLocalizable RealPoint : GeomUtils.vertices(inPoly)) {

			// double angleInRadians = Math.toRadians(angleInDegrees);
			double cosTheta = Math.cos(angle);
			double sinTheta = Math.sin(angle);

			double x = cosTheta * (RealPoint.getDoublePosition(0) - center
				.getDoublePosition(0)) - sinTheta * (RealPoint.getDoublePosition(1) -
					center.getDoublePosition(1)) + center.getDoublePosition(0);

			double y = sinTheta * (RealPoint.getDoublePosition(0) - center
				.getDoublePosition(0)) + cosTheta * (RealPoint.getDoublePosition(1) -
					center.getDoublePosition(1)) + center.getDoublePosition(1);

			out.add(new RealPoint(x, y));
		}

		return new DefaultWritablePolygon2D(out);
	}

	/**
	 * @param input the input Polygon
	 * @return The smallest enclosing rectangle, as a {@link Polygon2D}
	 */
	@Override
	public Polygon2D apply(final Polygon2D input) {
		// ensure validity of inputs
		if (input == null) throw new IllegalArgumentException(
			"Input cannot be null!");

		Polygon2D ch = convexHullFunc.apply(input);
		RealLocalizable cog = centroidFunc.apply(ch);

		Polygon2D minBounds = input;
		double minArea = Double.POSITIVE_INFINITY;
		// for each edge (i.e. line from P(i-1) to P(i)
		for (int i = 1; i < ch.numVertices() - 1; i++) {
			final double angle = Math.atan2(ch.vertex(i).getDoublePosition(1) - ch
				.vertex(i - 1).getDoublePosition(1), ch.vertex(i).getDoublePosition(0) -
					ch.vertex(i - 1).getDoublePosition(0));

			// rotate the polygon in such a manner that the line has an angle of 0
			final Polygon2D rotatedPoly = rotate(ch, -angle, cog);

			// get the bounds
			final Polygon2D bounds = boundingBoxFunc.apply(rotatedPoly);

			// calculate the area of the bounds
			final double area = areaFunc.apply(bounds).get();

			// if the area of the bounds is smaller, rotate it to match the
			// original polygon and save it.
			if (area < minArea) {
				minArea = area;
				minBounds = rotate(bounds, angle, cog);
			}
		}

		// edge (n-1) to 0
		final double angle = Math.atan2(ch.vertex(0).getDoublePosition(1) - ch
			.vertex(ch.numVertices() - 1).getDoublePosition(1), ch.vertex(0)
				.getDoublePosition(0) - ch.vertex(ch.numVertices() - 1)
					.getDoublePosition(0));

		// rotate the polygon in such a manner that the line has an angle of 0
		final Polygon2D rotatedPoly = rotate(ch, -angle, cog);

		// get the bounds
		final Polygon2D bounds = boundingBoxFunc.apply(rotatedPoly);

		// calculate the area of the bounds
		final double area = areaFunc.apply(bounds).get();

		// if the area of the bounds is smaller, rotate it to match the
		// original polygon and save it.
		if (area < minArea) {
			minArea = area;
			minBounds = rotate(bounds, angle, cog);
		}

		return minBounds;
	}

}