Algorithms.KdTree.Nearest C# (CSharp) Method

        private Point2D Nearest(KdNode node, RectHV rect, double x, double y, Point2D candidate) {
            if (node == null) {
                return candidate;
            }
            double dqn = 0;
            double drq = 0;
            var query = new Point2D(x, y);
            var nearest = candidate;

            if (nearest != null) {
                dqn = query.DistanceSquaredTo(nearest);
                drq = rect.DistanceSquaredTo(query);
            }

            if (nearest == null || dqn < drq) {
                var point = new Point2D(node.X, node.Y);
                if (nearest == null || dqn > query.DistanceSquaredTo(point)) {
                    nearest = point;
                }
            }

            var left = LeftRect(rect, node);
            var right = RightRect(rect, node);

            if (node.Vertical) {
                if (x < node.X) {
                    nearest = Nearest(node.Left, left, x, y, nearest);
                    nearest = Nearest(node.Right, right, x, y, nearest);
                }
                else {
                    nearest = Nearest(node.Right, right, x, y, nearest);
                    nearest = Nearest(node.Left, left, x, y, nearest);
                }
            }
            else {
                if (y < node.Y) {
                    nearest = Nearest(node.Left, left, x, y, nearest);
                    nearest = Nearest(node.Right, right, x, y, nearest);
                }
                else {
                    nearest = Nearest(node.Right, right, x, y, nearest);
                    nearest = Nearest(node.Left, left, x, y, nearest);
                }
            }

            return nearest;
        }