package org.opentrafficsim.core.geometry;
   
   import java.util.List;
   
   import org.djutils.draw.curve.Flattener2d;
   import org.djutils.draw.curve.OffsetCurve2d;
   import org.djutils.draw.curve.OffsetFlattener2d;
   import org.djutils.draw.function.ContinuousPiecewiseLinearFunction;
   import org.djutils.draw.line.PolyLine2d;
  import org.djutils.draw.point.DirectedPoint2d;
  import org.djutils.draw.point.Point2d;
  import org.djutils.exceptions.Throw;
  import org.djutils.math.functions.MathFunction.TupleSt;
  import org.opentrafficsim.base.geometry.OtsGeometryUtil;
  
  /**
   * Curve based on a poly line implementing all the features of {@link OffsetCurve2d}.
   * <p>
   * Copyright (c) 2024-2024 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
   * </p>
   * @author <a href="https://github.com/wjschakel">Wouter Schakel</a>
   */
  public class PolyLineCurve2d implements OffsetCurve2d
  {
  
      /** Poly line. */
      private final PolyLine2d line;
  
      /** Start direction. */
      private final double startDirection;
  
      /** End direction. */
      private final double endDirection;
  
      /**
       * Constructor.
       * @param line poly line
       * @param startDirection start direction
       * @param endDirection end direction
       */
      public PolyLineCurve2d(final PolyLine2d line, final double startDirection, final double endDirection)
      {
          this.line = line;
          this.startDirection = startDirection;
          this.endDirection = endDirection;
      }
  
      @Override
      public Double getDirection(final double fraction)
      {
          return fraction == 0.0 ? this.startDirection
                  : (fraction == 1.0 ? this.endDirection : this.line.getLocation(fraction).dirZ);
      }
  
      @Override
      public double getDirection(final double fraction, final ContinuousPiecewiseLinearFunction of)
      {
          return getDirection(fraction) + of.getDerivative(fraction);
      }
  
      @Override
      public DirectedPoint2d getPoint(final double fraction)
      {
          return this.line.getLocationFraction(fraction);
      }
  
      @Override
      public DirectedPoint2d getPoint(final double fraction, final ContinuousPiecewiseLinearFunction of)
      {
          DirectedPoint2d offsetPoint = OtsGeometryUtil.offsetPoint(getPoint(fraction), of.get(fraction));
          return new DirectedPoint2d(offsetPoint.x, offsetPoint.y, offsetPoint.dirZ + of.getDerivative(fraction));
      }
  
      @Override
      public double getLength()
      {
          return this.line.getLength();
      }
  
      @Override
      public PolyLine2d toPolyLine(final Flattener2d flattener)
      {
          return this.line;
      }
  
      @Override
      public PolyLine2d toPolyLine(final OffsetFlattener2d flattener, final ContinuousPiecewiseLinearFunction offsets)
      {
          Throw.whenNull(offsets, "Offsets may not be null.");
          double[] knots = new double[offsets.size()];
          double[] knotOffset = new double[offsets.size()];
          int i = 0;
          for (TupleSt st : offsets)
          {
              knots[i] = st.s();
              knotOffset[i] = st.t();
              i++;
          }
         PolyLine2d offsetLine = OtsGeometryUtil.offsetLine(this.line, knots, knotOffset);
         Point2d start = OtsGeometryUtil.offsetPoint(getStartPoint(), offsets.get(0.0));
         Point2d end = OtsGeometryUtil.offsetPoint(getEndPoint(), offsets.get(1.0));
         List<Point2d> points = offsetLine.getPointList();
         points.set(0, start);
         points.set(points.size() - 1, end);
         return new PolyLine2d(points);
     }
 
 }