

/*
 * 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.geom;

import java.io.Serializable;

import com.vividsolutions.jts.algorithm.*;

/**
 * Represents a line segment defined by two {@link Coordinate}s.
 * Provides methods to compute various geometric properties
 * and relationships of line segments.
 * <p>
 * This class is designed to be easily mutable (to the extent of
 * having its contained points public).
 * This supports a common pattern of reusing a single LineSegment
 * object as a way of computing segment properties on the
 * segments defined by arrays or lists of {@link Coordinate}s.
 *
 *@version 1.7
 */
public class LineSegment
  implements Comparable, Serializable
{
  private static final long serialVersionUID = 3252005833466256227L;

  public Coordinate p0, p1;

  public LineSegment(Coordinate p0, Coordinate p1) {
    this.p0 = p0;
    this.p1 = p1;
  }

  public LineSegment(LineSegment ls) {
    this(ls.p0, ls.p1);
  }

  public LineSegment() {
    this(new Coordinate(), new Coordinate());
  }

  public Coordinate getCoordinate(int i)
  {
    if (i == 0) return p0;
    return p1;
  }

  public void setCoordinates(LineSegment ls)
  {
    setCoordinates(ls.p0, ls.p1);
  }

  public void setCoordinates(Coordinate p0, Coordinate p1)
  {
    this.p0.x = p0.x;
    this.p0.y = p0.y;
    this.p1.x = p1.x;
    this.p1.y = p1.y;
  }

  /**
   * Computes the length of the line segment.
   * @return the length of the line segment
   */
  public double getLength()
  {
    return p0.distance(p1);
  }

  /**
   * Tests whether the segment is horizontal.
   *
   * @return <code>true</code> if the segment is horizontal
   */
  public boolean isHorizontal() { return p0.y == p1.y; }

  /**
   * Tests whether the segment is vertical.
   *
   * @return <code>true</code> if the segment is vertical
   */
  public boolean isVertical() { return p0.x == p1.x; }

  /**
   * Determines the orientation of a LineSegment relative to this segment.
   * The concept of orientation is specified as follows:
   * Given two line segments A and L,
   * <ul
   * <li>A is to the left of a segment L if A lies wholly in the
   * closed half-plane lying to the left of L
   * <li>A is to the right of a segment L if A lies wholly in the
   * closed half-plane lying to the right of L
   * <li>otherwise, A has indeterminate orientation relative to L. This
   * happens if A is collinear with L or if A crosses the line determined by L.
   * </ul>
   *
   * @param seg the LineSegment to compare
   *
   * @return 1 if <code>seg</code> is to the left of this segment
   * @return -1 if <code>seg</code> is to the right of this segment
   * @return 0 if <code>seg</code> has indeterminate orientation relative to this segment
   */
  public int orientationIndex(LineSegment seg)
  {
    int orient0 = CGAlgorithms.orientationIndex(p0, p1, seg.p0);
    int orient1 = CGAlgorithms.orientationIndex(p0, p1, seg.p1);
    // this handles the case where the points are L or collinear
    if (orient0 >= 0 && orient1 >= 0)
      return Math.max(orient0, orient1);
    // this handles the case where the points are R or collinear
    if (orient0 <= 0 && orient1 <= 0)
      return Math.max(orient0, orient1);
    // points lie on opposite sides ==> indeterminate orientation
    return 0;
  }
  /**
   * Reverses the direction of the line segment.
   */
  public void reverse()
  {
    Coordinate temp = p0;
    p0 = p1;
    p1 = temp;
  }

  /**
   * Puts the line segment into a normalized form.
   * This is useful for using line segments in maps and indexes when
   * topological equality rather than exact equality is desired.
   * A segment in normalized form has the first point smaller
   * than the second (according to the standard ordering on {@link Coordinate}).
   */
  public void normalize()
  {
    if (p1.compareTo(p0) < 0) reverse();
  }

  /**
   * Computes the angle that the vector defined by this segment
   * makes with the X-axis.
   * The angle will be in the range [ -PI, PI ] radians.
   *
   * @return the angle this segment makes with the X-axis (in radians)
   */
  public double angle()
  {
    return Math.atan2(p1.y - p0.y, p1.x - p0.x);
  }

  /**
   * Computes the midpoint of the segment
   *
   * @return the midpoint of the segment
   */
  public Coordinate midPoint()
  {
    return new Coordinate( (p0.x + p1.x) / 2,
                           (p0.y + p1.y) / 2);
  }

  /**
   * Computes the distance between this line segment and another segment.
   *
   * @return the distance to the other segment
   */
  public double distance(LineSegment ls)
  {
    return CGAlgorithms.distanceLineLine(p0, p1, ls.p0, ls.p1);
  }

  /**
   * Computes the distance between this line segment and a given point.
   *
   * @return the distance from this segment to the given point
   */
  public double distance(Coordinate p)
  {
    return CGAlgorithms.distancePointLine(p, p0, p1);
  }

  /**
   * Computes the perpendicular distance between the (infinite) line defined
   * by this line segment and a point.
   *
   * @return the perpendicular distance between the defined line and the given point
   */
  public double distancePerpendicular(Coordinate p)
  {
    return CGAlgorithms.distancePointLinePerpendicular(p, p0, p1);
  }

  /**
   * Computes the {@link Coordinate} that lies a given
   * fraction along the line defined by this segment.
   * A fraction of <code>0.0</code> returns the start point of the segment;
   * a fraction of <code>1.0</code> returns the end point of the segment.
   *
   * @param segmentLengthFraction the fraction of the segment length along the line
   * @return the point at that distance
   */
  public Coordinate pointAlong(double segmentLengthFraction)
  {
    Coordinate coord = new Coordinate();
    coord.x = p0.x + segmentLengthFraction * (p1.x - p0.x);
    coord.y = p0.y + segmentLengthFraction * (p1.y - p0.y);
    return coord;
  }

  /**
   * Computes the Projection Factor for the projection of the point p
   * onto this LineSegment.  The Projection Factor is the constant r
   * by which the vector for this segment must be multiplied to
   * equal the vector for the projection of p on the line
   * defined by this segment.
   */
  public double projectionFactor(Coordinate p)
  {
    if (p.equals(p0)) return 0.0;
    if (p.equals(p1)) return 1.0;
    // Otherwise, use comp.graphics.algorithms Frequently Asked Questions method
    /*     	      AC dot AB
                   r = ---------
                         ||AB||^2
                r has the following meaning:
                r=0 P = A
                r=1 P = B
                r<0 P is on the backward extension of AB
                r>1 P is on the forward extension of AB
                0<r<1 P is interior to AB
        */
    double dx = p1.x - p0.x;
    double dy = p1.y - p0.y;
    double len2 = dx * dx + dy * dy;
    double r = ( (p.x - p0.x) * dx + (p.y - p0.y) * dy )
              / len2;
    return r;
  }

  /**
   * Compute the projection of a point onto the line determined
   * by this line segment.
   * <p>
   * Note that the projected point
   * may lie outside the line segment.  If this is the case,
   * the projection factor will lie outside the range [0.0, 1.0].
   */
  public Coordinate project(Coordinate p)
  {
    if (p.equals(p0) || p.equals(p1)) return new Coordinate(p);

    double r = projectionFactor(p);
    Coordinate coord = new Coordinate();
    coord.x = p0.x + r * (p1.x - p0.x);
    coord.y = p0.y + r * (p1.y - p0.y);
    return coord;
  }
  /**
   * Project a line segment onto this line segment and return the resulting
   * line segment.  The returned line segment will be a subset of
   * the target line line segment.  This subset may be null, if
   * the segments are oriented in such a way that there is no projection.
   * <p>
   * Note that the returned line may have zero length (i.e. the same endpoints).
   * This can happen for instance if the lines are perpendicular to one another.
   *
   * @param seg the line segment to project
   * @return the projected line segment, or <code>null</code> if there is no overlap
   */
  public LineSegment project(LineSegment seg)
  {
    double pf0 = projectionFactor(seg.p0);
    double pf1 = projectionFactor(seg.p1);
    // check if segment projects at all
    if (pf0 >= 1.0 && pf1 >= 1.0) return null;
    if (pf0 <= 0.0 && pf1 <= 0.0) return null;

    Coordinate newp0 = project(seg.p0);
    if (pf0 < 0.0) newp0 = p0;
    if (pf0 > 1.0) newp0 = p1;

    Coordinate newp1 = project(seg.p1);
    if (pf1 < 0.0) newp1 = p0;
    if (pf1 > 1.0) newp1 = p1;

    return new LineSegment(newp0, newp1);
  }
  /**
   * Computes the closest point on this line segment to another point.
   * @param p the point to find the closest point to
   * @return a Coordinate which is the closest point on the line segment to the point p
   */
  public Coordinate closestPoint(Coordinate p)
  {
    double factor = projectionFactor(p);
    if (factor > 0 && factor < 1) {
      return project(p);
    }
    double dist0 = p0.distance(p);
    double dist1 = p1.distance(p);
    if (dist0 < dist1)
      return p0;
    return p1;
  }
  /**
   * Computes the closest points on two line segments.
   * @param p the point to find the closest point to
   * @return a pair of Coordinates which are the closest points on the line segments
   */
  public Coordinate[] closestPoints(LineSegment line)
  {
    // test for intersection
    Coordinate intPt = intersection(line);
    if (intPt != null) {
      return new Coordinate[] { intPt, intPt };
    }

    /**
     *  if no intersection closest pair contains at least one endpoint.
     * Test each endpoint in turn.
     */
    Coordinate[] closestPt = new Coordinate[2];
    double minDistance = Double.MAX_VALUE;
    double dist;

    Coordinate close00 = closestPoint(line.p0);
    minDistance = close00.distance(line.p0);
    closestPt[0] = close00;
    closestPt[1] = line.p0;

    Coordinate close01 = closestPoint(line.p1);
    dist = close01.distance(line.p1);
    if (dist < minDistance) {
      minDistance = dist;
      closestPt[0] = close01;
      closestPt[1] = line.p1;
    }

    Coordinate close10 = line.closestPoint(p0);
    dist = close10.distance(p0);
    if (dist < minDistance) {
      minDistance = dist;
      closestPt[0] = p0;
      closestPt[1] = close10;
    }

    Coordinate close11 = line.closestPoint(p1);
    dist = close11.distance(p1);
    if (dist < minDistance) {
      minDistance = dist;
      closestPt[0] = p1;
      closestPt[1] = close11;
    }

    return closestPt;
  }

  /**
   * Computes an intersection point between two segments, if there is one.
   * There may be 0, 1 or many intersection points between two segments.
   * If there are 0, null is returned. If there is 1 or more, a single one
   * is returned (chosen at the discretion of the algorithm).  If
   * more information is required about the details of the intersection,
   * the {@link RobustLineIntersector} class should be used.
   *
   * @param line
   * @return an intersection point, or <code>null</code> if there is none
   */
  public Coordinate intersection(LineSegment line)
  {
    LineIntersector li = new RobustLineIntersector();
    li.computeIntersection(p0, p1, line.p0, line.p1);
    if (li.hasIntersection())
      return li.getIntersection(0);
    return null;
  }

  /**
   *  Returns <code>true</code> if <code>other</code> has the same values for
   *  its points.
   *
   *@param  other  a <code>LineSegment</code> with which to do the comparison.
   *@return        <code>true</code> if <code>other</code> is a <code>LineSegment</code>
   *      with the same values for the x and y ordinates.
   */
  public boolean equals(Object o) {
    if (!(o instanceof LineSegment)) {
      return false;
    }
    LineSegment other = (LineSegment) o;
    return p0.equals(other.p0) && p1.equals(other.p1);
  }


  /**
   *  Compares this object with the specified object for order.
   *  Uses the standard lexicographic ordering for the points in the LineSegment.
   *
   *@param  o  the <code>LineSegment</code> with which this <code>LineSegment</code>
   *      is being compared
   *@return    a negative integer, zero, or a positive integer as this <code>LineSegment</code>
   *      is less than, equal to, or greater than the specified <code>LineSegment</code>
   */
  public int compareTo(Object o) {
    LineSegment other = (LineSegment) o;
    int comp0 = p0.compareTo(other.p0);
    if (comp0 != 0) return comp0;
    return p1.compareTo(other.p1);
  }

  /**
   *  Returns <code>true</code> if <code>other</code> is
   *  topologically equal to this LineSegment (e.g. irrespective
   *  of orientation).
   *
   *@param  other  a <code>LineSegment</code> with which to do the comparison.
   *@return        <code>true</code> if <code>other</code> is a <code>LineSegment</code>
   *      with the same values for the x and y ordinates.
   */
  public boolean equalsTopo(LineSegment other)
  {
    return
      p0.equals(other.p0) && p1.equals(other.p1)
      || p0.equals(other.p1) && p1.equals(other.p0);
  }

  public String toString()
  {
    return "LINESTRING( " +
        p0.x + " " + p0.y
        + ", " +
        p1.x + " " + p1.y + ")";
  }
}
