/*
    * 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;
  
  /**
   * Simple 2D line segment shape.
   *
   * @author Ronald Brill
   */
  public class Line2D implements Shape2D {
  
      private final double startX_;
      private final double startY_;
      private final double endX_;
      private final double endY_;
      private final boolean isVertical_;
  
      private final double slope_;
      private final double yIntercept_;
  
      /**
       * Creates a new line segment between the two given points.
       *
       * @param start the start point
       * @param end the end point
       */
      public Line2D(final Point2D start, final Point2D end) {
          this(start.getX(), start.getY(), end.getX(), end.getY());
      }
  
      /**
       * Creates a new line segment between the two given coordinates.
       *
       * @param x1 the x coordinate of the start point
       * @param y1 the y coordinate of the start point
       * @param x2 the x coordinate of the end point
       * @param y2 the y coordinate of the end point
       */
      public Line2D(final double x1, final double y1, final double x2, final double y2) {
          startX_ = x1;
          startY_ = y1;
          endX_ = x2;
          endY_ = y2;
  
          isVertical_ = Math.abs(startX_ - endX_) < EPSILON;
          if (isVertical_) {
              slope_ = Double.NaN;
              yIntercept_ = Double.NaN;
          }
          else {
              // y = slope * x + b
              slope_ = (endY_ - startY_) / (endX_ - startX_);
              yIntercept_ = startY_ - slope_ * startX_;
          }
      }
  
      /**
       * Returns the intersection point of this line with the given line,
       * or {@code null} if the lines are parallel.
       *
       * @param line the line to intersect with
       * @return the intersection point, or {@code null} if the lines are parallel
       */
      public Point2D intersect(final Line2D line) {
          if (isVertical_ && line.isVertical_) {
              return null;
          }
  
          if (isVertical_ && !line.isVertical_) {
              final double intersectY = line.slope_ * startX_ + line.yIntercept_;
              return new Point2D(startX_, intersectY);
          }
  
          if (!isVertical_ && line.isVertical_) {
              final double intersectY = slope_ * line.startX_ + yIntercept_;
              return new Point2D(line.startX_, intersectY);
          }
  
          // parallel?
          if (Math.abs(slope_ - line.slope_) < EPSILON) {
              return null;
          }
  
          // x = (n2-n1)/(m1-m2)
          final double intersectX = (line.yIntercept_ - yIntercept_) / (slope_ - line.slope_);
          // y = m2*x+n2
          final double intersectY = slope_ * intersectX + yIntercept_;
         return new Point2D(intersectX, intersectY);
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean contains(final double x, final double y) {
         if (isVertical_) {
             if (Math.abs(startX_ - x) > EPSILON) {
                 return false;
             }
         }
         else {
             final double testY = slope_ * x + yIntercept_;
             if (Math.abs(y - testY) > EPSILON) {
                 return false;
             }
 
             if (x < startX_ && x < endX_
                     || (x > startX_ && x > endX_)) {
                 return false;
             }
         }
 
         if (y < startY_ && y < endY_
                 || (y > startY_ && y > endY_)) {
             return false;
         }
 
         return true;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isEmpty() {
         return Math.abs(startX_ - endX_) < EPSILON && Math.abs(startY_ - endY_) < EPSILON;
     }
 
     @Override
     public String toString() {
         return "Line2D [ (" + startX_ + ", " + startY_ + "), (" + endX_ + ", " + endY_
                 + "), " + (isVertical_ ? "isVertical" : "y = " + slope_ + "*x + " + yIntercept_ + "]");
     }
 }