// ******************************************************************************
   //
   // Title:       Force Field X.
   // Description: Force Field X - Software for Molecular Biophysics.
   // Copyright:   Copyright (c) Michael J. Schnieders 2001-2025.
   //
   // This file is part of Force Field X.
   //
   // Force Field X is free software; you can redistribute it and/or modify it
  // under the terms of the GNU General Public License version 3 as published by
  // the Free Software Foundation.
  //
  // Force Field X 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 General Public License for more
  // details.
  //
  // You should have received a copy of the GNU General Public License along with
  // Force Field X; if not, write to the Free Software Foundation, Inc., 59 Temple
  // Place, Suite 330, Boston, MA 02111-1307 USA
  //
  // Linking this library statically or dynamically with other modules is making a
  // combined work based on this library. Thus, the terms and conditions of the
  // GNU General Public License cover the whole combination.
  //
  // As a special exception, the copyright holders of this library give you
  // permission to link this library with independent modules to produce an
  // executable, regardless of the license terms of these independent modules, and
  // to copy and distribute the resulting executable under terms of your choice,
  // provided that you also meet, for each linked independent module, the terms
  // and conditions of the license of that module. An independent module is a
  // module which is not derived from or based on this library. If you modify this
  // library, you may extend this exception to your version of the library, but
  // you are not obligated to do so. If you do not wish to do so, delete this
  // exception statement from your version.
  //
  // ******************************************************************************
  package ffx.numerics.quickhull;
  
  /**
   * Represents the half-edges that surround each face in a counter-clockwise
   * direction.
   *
   * @author John E. Lloyd, Fall 2004
   * @author Michael J. Schnieders
   * @since 1.0
   */
  public class HalfEdge {
  
    /**
     * The vertex associated with the head of this half-edge.
     */
    protected Vertex vertex;
  
    /**
     * Triangular face associated with this half-edge.
     */
    protected Face face;
  
    /**
     * Next half-edge in the triangle.
     */
    protected HalfEdge next;
  
    /**
     * Previous half-edge in the triangle.
     */
    protected HalfEdge prev;
  
    /**
     * Half-edge associated with the opposite triangle adjacent to this edge.
     */
    protected HalfEdge opposite;
  
    /**
     * Constructs a HalfEdge with head vertex <code>v</code> and left-hand
     * triangular face <code>f</code>.
     *
     * @param v head vertex
     * @param f left-hand triangular face
     */
    public HalfEdge(Vertex v, Face f) {
      vertex = v;
      face = f;
    }
  
    /**
     * Constructs an uninitialized HalfEdge.
     * Fields may be set later via mutators.
     */
    public HalfEdge() {
    }
  
    /**
     * Sets the value of the next edge adjacent (counter-clockwise) to this one
     * within the triangle.
     *
     * @param edge next adjacent edge
     */
   public void setNext(HalfEdge edge) {
     next = edge;
   }
 
   /**
    * Gets the value of the next edge adjacent (counter-clockwise) to this one
    * within the triangle.
    *
    * @return next adjacent edge
    */
   public HalfEdge getNext() {
     return next;
   }
 
   /**
    * Sets the value of the previous edge adjacent (clockwise) to this one
    * within the triangle.
    *
    * @param edge previous adjacent edge
    */
   public void setPrev(HalfEdge edge) {
     prev = edge;
   }
 
   /**
    * Gets the value of the previous edge adjacent (clockwise) to this one
    * within the triangle.
    *
    * @return previous adjacent edge
    */
   public HalfEdge getPrev() {
     return prev;
   }
 
   /**
    * Returns the triangular face located to the left of this half-edge.
    *
    * @return left-hand triangular face
    */
   public Face getFace() {
     return face;
   }
 
   /**
    * Returns the half-edge opposite to this half-edge.
    *
    * @return opposite half-edge
    */
   public HalfEdge getOpposite() {
     return opposite;
   }
 
   /**
    * Sets the half-edge opposite to this half-edge.
    *
    * @param edge opposite half-edge
    */
   public void setOpposite(HalfEdge edge) {
     opposite = edge;
     edge.opposite = this;
   }
 
   /**
    * Returns the head vertex associated with this half-edge.
    *
    * @return head vertex
    */
   public Vertex head() {
     return vertex;
   }
 
   /**
    * Returns the tail vertex associated with this half-edge.
    *
    * @return tail vertex
    */
   public Vertex tail() {
     return prev != null ? prev.vertex : null;
   }
 
   /**
    * Returns the opposite triangular face associated with this half-edge.
    *
    * @return opposite triangular face
    */
   public Face oppositeFace() {
     return opposite != null ? opposite.face : null;
   }
 
   /**
    * Produces a string identifying this half-edge by the point index values of
    * its tail and head vertices.
    *
    * @return identifying string
    */
   public String getVertexString() {
     if (tail() != null) {
       return tail().index + "-" + head().index;
     } else {
       return "?-" + head().index;
     }
   }
 
   /**
    * Returns the length of this half-edge.
    *
    * @return half-edge length
    */
   public double length() {
     if (tail() != null) {
       return head().pnt.distance(tail().pnt);
     } else {
       return -1;
     }
   }
 
   /**
    * Returns the length squared of this half-edge.
    *
    * @return half-edge length squared
    */
   public double lengthSquared() {
     if (tail() != null) {
       return head().pnt.distanceSquared(tail().pnt);
     } else {
       return -1;
     }
   }
 }