/*
 *    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.topograph2D.index;

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

import org.geotools.geometry.iso.topograph2D.Edge;

/**
 * Finds all intersections in one or two sets of edges, using an x-axis
 * sweepline algorithm in conjunction with Monotone Chains. While still O(n^2)
 * in the worst case, this algorithm drastically improves the average-case time.
 * The use of MonotoneChains as the items in the index seems to offer an
 * improvement in performance over a sweep-line alone.
 * 
 *
 *
 *
 * @source $URL$
 */
public class SimpleMonotoneChainSweepLineIntersector extends EdgeSetIntersector {

	List events = new ArrayList();

	// statistics information
	int nOverlaps;

	/**
	 * A SimpleMCSweepLineIntersector creates monotone chains from the edges and
	 * compares them using a simple sweep-line along the x-axis.
	 */
	public SimpleMonotoneChainSweepLineIntersector() {
	}

	public void computeIntersections(List edges, SegmentIntersector si,
			boolean testAllSegments) {
		if (testAllSegments)
			add(edges, null);
		else
			add(edges);
		computeIntersections(si);
	}

	public void computeIntersections(List edges0, List edges1,
			SegmentIntersector si) {
		add(edges0, edges0);
		add(edges1, edges1);
		computeIntersections(si);
	}

	private void add(List edges) {
		for (Iterator i = edges.iterator(); i.hasNext();) {
			Edge edge = (Edge) i.next();
			// edge is its own group
			add(edge, edge);
		}
	}

	private void add(List edges, Object edgeSet) {
		for (Iterator i = edges.iterator(); i.hasNext();) {
			Edge edge = (Edge) i.next();
			add(edge, edgeSet);
		}
	}

	private void add(Edge edge, Object edgeSet) {
		MonotoneChainEdge mce = edge.getMonotoneChainEdge();
		int[] startIndex = mce.getStartIndexes();
		for (int i = 0; i < startIndex.length - 1; i++) {
			MonotoneChain mc = new MonotoneChain(mce, i);
			SweepLineEvent insertEvent = new SweepLineEvent(edgeSet, mce
					.getMinX(i), null, mc);
			events.add(insertEvent);
			events.add(new SweepLineEvent(edgeSet, mce.getMaxX(i), insertEvent,
					mc));
		}
	}

	/**
	 * Because Delete Events have a link to their corresponding Insert event, it
	 * is possible to compute exactly the range of events which must be compared
	 * to a given Insert event object.
	 */
	private void prepareEvents() {
		Collections.sort(events);
		for (int i = 0; i < events.size(); i++) {
			SweepLineEvent ev = (SweepLineEvent) events.get(i);
			if (ev.isDelete()) {
				ev.getInsertEvent().setDeleteEventIndex(i);
			}
		}
	}

	private void computeIntersections(SegmentIntersector si) {
		nOverlaps = 0;
		prepareEvents();

		for (int i = 0; i < events.size(); i++) {
			SweepLineEvent ev = (SweepLineEvent) events.get(i);
			if (ev.isInsert()) {
				processOverlaps(i, ev.getDeleteEventIndex(), ev, si);
			}
		}
	}

	private void processOverlaps(int start, int end, SweepLineEvent ev0,
			SegmentIntersector si) {
		MonotoneChain mc0 = (MonotoneChain) ev0.getObject();
		/**
		 * Since we might need to test for self-intersections, include current
		 * insert event object in list of event objects to test. Last index can
		 * be skipped, because it must be a Delete event.
		 */
		for (int i = start; i < end; i++) {
			SweepLineEvent ev1 = (SweepLineEvent) events.get(i);
			if (ev1.isInsert()) {
				MonotoneChain mc1 = (MonotoneChain) ev1.getObject();
				// don't compare edges in same group
				// null group indicates that edges should be compared
				if (ev0.edgeSet == null || (ev0.edgeSet != ev1.edgeSet)) {
					mc0.computeIntersections(mc1, si);
					nOverlaps++;
				}
			}
		}
	}
}