/*
 * Copyright (c) 2016 Vivid Solutions.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 *
 * http://www.eclipse.org/org/documents/edl-v10.php.
 */
package org.locationtech.jts.densify;

import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.CoordinateList;
import org.locationtech.jts.geom.CoordinateSequence;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.LineSegment;
import org.locationtech.jts.geom.LineString;
import org.locationtech.jts.geom.MultiPolygon;
import org.locationtech.jts.geom.Polygon;
import org.locationtech.jts.geom.PrecisionModel;
import org.locationtech.jts.geom.util.GeometryTransformer;

/**
 * Densifies a {@link Geometry} by inserting extra vertices along the line segments
 * contained in the geometry. 
 * All segments in the created densified geometry will be no longer than
 * than the given distance tolerance.
 * Densified polygonal geometries are guaranteed to be topologically correct.
 * The coordinates created during densification respect the input geometry's
 * {@link PrecisionModel}.
 * <p>
 * <b>Note:</b> At some future point this class will
 * offer a variety of densification strategies.
 * 
 * @author Martin Davis
 */
public class Densifier {
	/**
	 * Densifies a geometry using a given distance tolerance,
   * and respecting the input geometry's {@link PrecisionModel}.
	 * 
	 * @param geom the geometry to densify
	 * @param distanceTolerance the distance tolerance to densify
	 * @return the densified geometry
	 */
	public static Geometry densify(Geometry geom, double distanceTolerance) {
		Densifier densifier = new Densifier(geom);
		densifier.setDistanceTolerance(distanceTolerance);
		return densifier.getResultGeometry();
	}

	/**
	 * Densifies a coordinate sequence.
	 * 
	 * @param pts
	 * @param distanceTolerance
	 * @return the densified coordinate sequence
	 */
	private static Coordinate[] densifyPoints(Coordinate[] pts,
			double distanceTolerance, PrecisionModel precModel) {
		LineSegment seg = new LineSegment();
		CoordinateList coordList = new CoordinateList();
		for (int i = 0; i < pts.length - 1; i++) {
			seg.p0 = pts[i];
			seg.p1 = pts[i + 1];
			coordList.add(seg.p0, false);
			double len = seg.getLength();
			int densifiedSegCount = (int) (len / distanceTolerance) + 1;
			if (densifiedSegCount > 1) {
				double densifiedSegLen = len / densifiedSegCount;
				for (int j = 1; j < densifiedSegCount; j++) {
					double segFract = (j * densifiedSegLen) / len;
					Coordinate p = seg.pointAlong(segFract);
          precModel.makePrecise(p);
					coordList.add(p, false);
				}
			}
		}
		coordList.add(pts[pts.length - 1], false);
		return coordList.toCoordinateArray();
	}

	private Geometry inputGeom;

	private double distanceTolerance;

	/**
	 * Creates a new densifier instance.
	 * 
	 * @param inputGeom
	 */
	public Densifier(Geometry inputGeom) {
		this.inputGeom = inputGeom;
	}

	/**
	 * Sets the distance tolerance for the densification. All line segments
	 * in the densified geometry will be no longer than the distance tolerance.
	 * simplified geometry will be within this distance of the original geometry.
	 * The distance tolerance must be positive.
	 * 
	 * @param distanceTolerance
	 *          the densification tolerance to use
	 */
	public void setDistanceTolerance(double distanceTolerance) {
		if (distanceTolerance <= 0.0)
			throw new IllegalArgumentException("Tolerance must be positive");
		this.distanceTolerance = distanceTolerance;
	}

	/**
	 * Gets the densified geometry.
	 * 
	 * @return the densified geometry
	 */
	public Geometry getResultGeometry() {
		return (new DensifyTransformer()).transform(inputGeom);
	}

	class DensifyTransformer extends GeometryTransformer {
		protected CoordinateSequence transformCoordinates(
				CoordinateSequence coords, Geometry parent) {
			Coordinate[] inputPts = coords.toCoordinateArray();
			Coordinate[] newPts = Densifier
					.densifyPoints(inputPts, distanceTolerance, parent.getPrecisionModel());
			// prevent creation of invalid linestrings
			if (parent instanceof LineString && newPts.length == 1) {
				newPts = new Coordinate[0];
			}
			return factory.getCoordinateSequenceFactory().create(newPts);
		}

		protected Geometry transformPolygon(Polygon geom, Geometry parent) {
			Geometry roughGeom = super.transformPolygon(geom, parent);
			// don't try and correct if the parent is going to do this
			if (parent instanceof MultiPolygon) {
				return roughGeom;
			}
			return createValidArea(roughGeom);
		}

		protected Geometry transformMultiPolygon(MultiPolygon geom, Geometry parent) {
			Geometry roughGeom = super.transformMultiPolygon(geom, parent);
			return createValidArea(roughGeom);
		}

		/**
		 * Creates a valid area geometry from one that possibly has bad topology
		 * (i.e. self-intersections). Since buffer can handle invalid topology, but
		 * always returns valid geometry, constructing a 0-width buffer "corrects"
		 * the topology. Note this only works for area geometries, since buffer
		 * always returns areas. This also may return empty geometries, if the input
		 * has no actual area.
		 * 
		 * @param roughAreaGeom
		 *          an area geometry possibly containing self-intersections
		 * @return a valid area geometry
		 */
		private Geometry createValidArea(Geometry roughAreaGeom) {
			return roughAreaGeom.buffer(0.0);
		}
	}

}