


/*
 * The JTS Topology Suite is a collection of Java classes that
 * implement the fundamental operations required to validate a given
 * geo-spatial data set to a known topological specification.
 *
 * Copyright (C) 2001 Vivid Solutions
 *
 * 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; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * 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.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * For more information, contact:
 *
 *     Vivid Solutions
 *     Suite #1A
 *     2328 Government Street
 *     Victoria BC  V8T 5G5
 *     Canada
 *
 *     (250)385-6040
 *     www.vividsolutions.com
 */
package com.vividsolutions.jts.geomgraph;

/**
 * @version 1.7
 */
import com.vividsolutions.jts.geom.Coordinate;

/**
 * Utility functions for working with quadrants, which are numbered as follows:
 * <pre>
 * 1 | 0
 * --+--
 * 2 | 3
 * <pre>
 *
 * @version 1.7
 */
public class Quadrant {
  /**
   * Returns the quadrant of a directed line segment (specified as x and y
   * displacements, which cannot both be 0).
   */
  public static int quadrant(double dx, double dy)
  {
    if (dx == 0.0 && dy == 0.0)
      throw new IllegalArgumentException("Cannot compute the quadrant for point ( "+ dx + ", " + dy + " )" );
    if (dx >= 0) {
      if (dy >= 0)
        return 0;
      else
        return 3;
    }
    else {
	if (dy >= 0)
          return 1;
	else
          return 2;
    }
  }

  /**
   * Returns the quadrant of a directed line segment from p0 to p1.
   */
  public static int quadrant(Coordinate p0, Coordinate p1)
  {
    double dx = p1.x - p0.x;
    double dy = p1.y - p0.y;
    if (dx == 0.0 && dy == 0.0)
      throw new IllegalArgumentException("Cannot compute the quadrant for two identical points " + p0);
    return quadrant(dx, dy);
  }

  /**
   * Returns true if the quadrants are 1 and 3, or 2 and 4
   */
  public static boolean isOpposite(int quad1, int quad2)
  {
    if (quad1 == quad2) return false;
    int diff = (quad1 - quad2 + 4) % 4;
    // if quadrants are not adjacent, they are opposite
    if (diff == 2) return true;
    return false;
  }

  /** 
   * Returns the right-hand quadrant of the halfplane defined by the two quadrants,
   * or -1 if the quadrants are opposite, or the quadrant if they are identical.
   */
  public static int commonHalfPlane(int quad1, int quad2)
  {
    // if quadrants are the same they do not determine a unique common halfplane.
    // Simply return one of the two possibilities
    if (quad1 == quad2) return quad1;
    int diff = (quad1 - quad2 + 4) % 4;
    // if quadrants are not adjacent, they do not share a common halfplane
    if (diff == 2) return -1;
    //
    int min = (quad1 < quad2) ? quad1 : quad2;
    int max = (quad1 > quad2) ? quad1 : quad2;
    // for this one case, the righthand plane is NOT the minimum index;
    if (min == 0 && max == 3) return 3;
    // in general, the halfplane index is the minimum of the two adjacent quadrants
    return min;
  }

  /**
   * Returns whether the given quadrant lies within the given halfplane (specified
   * by its right-hand quadrant).
   */
  public static boolean isInHalfPlane(int quad, int halfPlane)
  {
    if (halfPlane == 3) {
      return quad == 3 || quad == 0;
    }
    return quad == halfPlane || quad == halfPlane + 1;
  }
    
  /**
   * Returns true if the given quadrant is 0 or 1.
   */
  public static boolean isNorthern(int quad)
  {
    return quad == 0 || quad == 1;
  }
}
