/*
    * Copyright (c) 2002-2026 Gargoyle Software Inc.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    * https://www.apache.org/licenses/LICENSE-2.0
    *
    * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.htmlunit.util.geometry;
  
  import java.util.ArrayList;
  
  /**
   * Simple 2D polygon shape.
   *
   * @author Ronald Brill
   */
  public class Polygon2D implements Shape2D {
      private final ArrayList<Point2D> points_;
      private final Rectangle2D boundingBox_;
  
      /**
       * Creates a new polygon starting at the given point.
       * Use {@link #lineTo(double, double)} to add further corner points.
       *
       * @param startX the x coordinate of the first point
       * @param startY the y coordinate of the first point
       */
      public Polygon2D(final double startX, final double startY) {
          points_ = new ArrayList<>();
          points_.add(new Point2D(startX, startY));
          boundingBox_ = new Rectangle2D(startX, startY, startX, startY);
      }
  
      /**
       * Adds another corner point to the polygon.
       *
       * @param x the x coordinate of the corner to add
       * @param y the y coordinate of the corner to add
       * @return this instance to support fluent-style construction
       */
      public Polygon2D lineTo(final double x, final double y) {
          points_.add(new Point2D(x, y));
          boundingBox_.extend(x, y);
  
          return this;
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public boolean contains(final double x, final double y) {
          if (!boundingBox_.contains(x, y)) {
              return false;
          }
  
          final double outsideX = boundingBox_.getLeft() - EPSILON;
          final double outsideY = boundingBox_.getBottom();
  
          final Line2D testLine = new Line2D(outsideX, outsideY, x, y);
          int intersectionCount = 0;
  
          int i = 0;
          while (i < points_.size() - 1) {
              final Point2D start = points_.get(i);
              final Point2D end = points_.get(++i);
              final Line2D border = new Line2D(start, end);
  
              if (border.contains(x, y)) {
                  return true;
              }
  
              final Point2D intersectionPoint = border.intersect(testLine);
              if (intersectionPoint != null
                      && border.contains(intersectionPoint.getX(), intersectionPoint.getY())
                      && testLine.contains(intersectionPoint.getX(), intersectionPoint.getY())) {
                  intersectionCount++;
              }
          }
  
          final Point2D start = points_.get(0);
          final Point2D end = points_.get(i);
          final Line2D border = new Line2D(start, end);
  
          if (border.contains(x, y)) {
              return true;
          }
  
          final Point2D intersectionPoint = border.intersect(testLine);
          if (intersectionPoint != null
                  && border.contains(intersectionPoint.getX(), intersectionPoint.getY())
                  && testLine.contains(intersectionPoint.getX(), intersectionPoint.getY())) {
             intersectionCount++;
         }
 
         return intersectionCount % 2 != 0;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isEmpty() {
         return points_.size() < 2;
     }
 
     @Override
     public String toString() {
         return "Polygon2D []";
     }
 }