/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *    
 *    (C) 2001-2006  Vivid Solutions
 *    (C) 2001-2008, Open Source Geospatial Foundation (OSGeo)
 *    
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *    Lesser General Public License for more details.
 */
package org.geotools.geometry.iso.operation.relate;


import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.geotools.geometry.iso.topograph2D.Coordinate;
import org.geotools.geometry.iso.topograph2D.Edge;
import org.geotools.geometry.iso.topograph2D.EdgeEnd;
import org.geotools.geometry.iso.topograph2D.EdgeIntersection;
import org.geotools.geometry.iso.topograph2D.EdgeIntersectionList;
import org.geotools.geometry.iso.topograph2D.Label;

/**
 * An EdgeEndBuilder creates EdgeEnds for all the "split edges" created by the
 * intersections determined for an Edge.
 * Computes the {@link EdgeEnd}s which arise from a noded {@link Edge}.
 *
 *
 *
 * @source $URL$
 */
public class EdgeEndBuilder {

	public EdgeEndBuilder() {
	}

	public List computeEdgeEnds(Iterator edges) {
		List l = new ArrayList();
		for (Iterator i = edges; i.hasNext();) {
			Edge e = (Edge) i.next();
			this.computeEdgeEnds(e, l);
		}
		return l;
	}

	/**
	 * Creates stub edges for all the intersections in this Edge (if any) and
	 * inserts them into the graph.
	 * @param edge
	 * @param l
	 */
	public void computeEdgeEnds(Edge edge, List l) {
		EdgeIntersectionList eiList = edge.getEdgeIntersectionList();
		// Debug.print(eiList);
		// ensure that the list has entries for the first and last point of the
		// edge
		eiList.addEndpoints();

		Iterator it = eiList.iterator();
		EdgeIntersection eiPrev = null;
		EdgeIntersection eiCurr = null;
		// no intersections, so there is nothing to do
		if (!it.hasNext())
			return;
		EdgeIntersection eiNext = (EdgeIntersection) it.next();
		do {
			eiPrev = eiCurr;
			eiCurr = eiNext;
			eiNext = null;
			if (it.hasNext())
				eiNext = (EdgeIntersection) it.next();

			if (eiCurr != null) {
				createEdgeEndForPrev(edge, l, eiCurr, eiPrev);
				createEdgeEndForNext(edge, l, eiCurr, eiNext);
			}

		} while (eiCurr != null);

	}

	/**
	 * Create a EdgeStub for the edge before the intersection eiCurr. The
	 * previous intersection is provided in case it is the endpoint for the stub
	 * edge. Otherwise, the previous point from the parent edge will be the
	 * endpoint. <br>
	 * eiCurr will always be an EdgeIntersection, but eiPrev may be null.
	 * @param edge
	 * @param l
	 * @param eiCurr
	 * @param eiPrev
	 */
	private void createEdgeEndForPrev(Edge edge, List l, EdgeIntersection eiCurr,
			EdgeIntersection eiPrev) {

		int iPrev = eiCurr.segmentIndex;
		if (eiCurr.dist == 0.0) {
			// if at the start of the edge there is no previous edge
			if (iPrev == 0)
				return;
			iPrev--;
		}
		Coordinate pPrev = edge.getCoordinate(iPrev);
		// if prev intersection is past the previous vertex, use it instead
		if (eiPrev != null && eiPrev.segmentIndex >= iPrev)
			pPrev = eiPrev.coord;

		Label label = new Label(edge.getLabel());
		// since edgeStub is oriented opposite to it's parent edge, have to flip
		// sides for edge label
		label.flip();
		EdgeEnd e = new EdgeEnd(edge, eiCurr.coord, pPrev, label);
		// e.print(System.out); System.out.println();
		l.add(e);
	}

	/**
	 * Create a StubEdge for the edge after the intersection eiCurr. The next
	 * intersection is provided in case it is the endpoint for the stub edge.
	 * Otherwise, the next point from the parent edge will be the endpoint. <br>
	 * eiCurr will always be an EdgeIntersection, but eiNext may be null.
	 * @param edge
	 * @param l
	 * @param eiCurr
	 * @param eiNext
	 */
	private void createEdgeEndForNext(Edge edge, List l, EdgeIntersection eiCurr,
			EdgeIntersection eiNext) {

		int iNext = eiCurr.segmentIndex + 1;
		// if there is no next edge there is nothing to do
		if (iNext >= edge.getNumPoints() && eiNext == null)
			return;

		Coordinate pNext = edge.getCoordinate(iNext);

		// if the next intersection is in the same segment as the current, use
		// it as the endpoint
		if (eiNext != null && eiNext.segmentIndex == eiCurr.segmentIndex)
			pNext = eiNext.coord;

		EdgeEnd e = new EdgeEnd(edge, eiCurr.coord, pNext, new Label(edge
				.getLabel()));
		// Debug.println(e);
		l.add(e);
	}

}