/*
 * 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.operation.relate;

/**
 * An EdgeEndBuilder creates EdgeEnds for all the "split edges"
 * created by the
 * intersections determined for an Edge.
 *
 * @version 1.7
 */
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geomgraph.Edge;
import org.locationtech.jts.geomgraph.EdgeEnd;
import org.locationtech.jts.geomgraph.EdgeIntersection;
import org.locationtech.jts.geomgraph.EdgeIntersectionList;
import org.locationtech.jts.geomgraph.Label;

/**
 * Computes the {@link EdgeEnd}s which arise from a noded {@link Edge}.
 *
 * @version 1.7
 */
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();
      computeEdgeEnds(e, l);
    }
    return l;
  }

  /**
   * Creates stub edges for all the intersections in this
   * Edge (if any) and inserts them into the graph.
   */
  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.
   */
  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.
     */
  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);
  }

}