package org.opentrafficsim.base.geometry;
   
   import java.util.List;
   
   import org.djunits.value.vdouble.scalar.Direction;
   import org.djutils.draw.line.PolyLine2d;
   import org.djutils.draw.line.Ray2d;
   import org.djutils.draw.point.OrientedPoint2d;
   import org.djutils.draw.point.Point2d;
  import org.djutils.exceptions.Throw;
  
  /**
   * Adds a direction at the start and end point relative to its super class {@code OtsLine2d}, as the first and last segment may
   * not have the same direction as a theoretical line the segments are a numerical approach of. These directions are used in a
   * few methods which alter the result from the super class. The most notable addition of this class is
   * {@code directionalOffsetLine}.
   */
  public class DirectionalPolyLine extends OtsLine2d
  {
      /** */
      private static final long serialVersionUID = 20241130L;
  
      /** Start direction. */
      private final Direction startDirection;
  
      /** End direction. */
      private final Direction endDirection;
  
      /**
       * Constructor.
       * @param line base line
       * @param startDirection start direction
       * @param endDirection end direction
       */
      public DirectionalPolyLine(final PolyLine2d line, final Direction startDirection, final Direction endDirection)
      {
          super(line);
          Throw.whenNull(startDirection, "startDirection");
          Throw.whenNull(endDirection, "endDirection");
          this.startDirection = startDirection;
          this.endDirection = endDirection;
      }
  
      /**
       * Returns line at a fixed offset, adhering to end-point directions.
       * @param offset offset
       * @return offset line
       */
      public DirectionalPolyLine directionalOffsetLine(final double offset)
      {
          PolyLine2d offsetLine = offsetLine(offset);
          OrientedPoint2d start = new OrientedPoint2d(getFirst().x, getFirst().y, this.startDirection.si);
          OrientedPoint2d end = new OrientedPoint2d(getLast().x, getLast().y, this.endDirection.si);
          List<Point2d> points = offsetLine.getPointList();
          points.set(0, OtsGeometryUtil.offsetPoint(start, offset));
          points.set(points.size() - 1, OtsGeometryUtil.offsetPoint(end, offset));
          return new DirectionalPolyLine(new PolyLine2d(points), this.startDirection, this.endDirection);
      }
  
      /**
       * Returns line at a fixed offset, adhering to end-point directions.
       * @param startOffset offset at start
       * @param endOffset offset at end
       * @return offset line
       */
      public DirectionalPolyLine directionalOffsetLine(final double startOffset, final double endOffset)
      {
          PolyLine2d start = directionalOffsetLine(startOffset);
          PolyLine2d end = directionalOffsetLine(endOffset);
          return new DirectionalPolyLine(start.transitionLine(end, (f) -> f), this.startDirection, this.endDirection);
      }
  
      @Override
      public DirectionalPolyLine extractFractional(final double start, final double end)
      {
          return new DirectionalPolyLine(super.extractFractional(start, end),
                  Direction.instantiateSI(getLocationFraction(start).phi), Direction.instantiateSI(getLocationFraction(end).phi));
      }
  
      @Override
      public Ray2d getLocationFraction(final double fraction)
      {
          Ray2d ray = super.getLocationFraction(fraction);
          if (fraction == 0.0)
          {
              ray = new Ray2d(ray, this.startDirection.si);
          }
          else if (fraction == 1.0)
          {
              ray = new Ray2d(ray, this.endDirection.si);
          }
          return ray;
      }
  
      /**
       * Fractional projection applied with the internal start and end direction.
       * @param x x-coordinate
       * @param y y-coordinate
       * @param fallback fallback method
      * @return fraction along line which it the projection of the given coordinate
      */
     public double projectFractional(final double x, final double y, final FractionalFallback fallback)
     {
         return projectFractional(this.startDirection, this.endDirection, x, y, fallback);
     }
 
     /**
      * Returns the start direction.
      * @return start direction
      */
     public Direction getStartDirection()
     {
         return this.startDirection;
     }
 
     /**
      * Returns the end direction.
      * @return end direction
      */
     public Direction getEndDirection()
     {
         return this.endDirection;
     }
 }