using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NetTopologySuite.Geometries;

namespace FortAnalysis
{
    public class PolygonSplit
    {
        // 找到自相交多边形的交点
        private static List<Tuple<double, double>> FindIntersectionPoints(List<Tuple<double, double>> coordinates)
        {
            List<Tuple<double, double>> intersectionPoints = new List<Tuple<double, double>>();

            for (int i = 0; i < coordinates.Count; i++)
            {
                var edge1Start = coordinates[i];
                var edge1End = coordinates[(i + 1) % coordinates.Count];

                for (int j = i + 2; j < coordinates.Count + i - 1; j++)
                {
                    var edge2Start = coordinates[j % coordinates.Count];
                    var edge2End = coordinates[(j + 1) % coordinates.Count];

                    var intersection = FindIntersection(edge1Start, edge1End, edge2Start, edge2End);
                    if (intersection != null)
                    {
                        intersectionPoints.Add(intersection);
                    }
                }
            }

            return intersectionPoints;
        }

        // 找到两条边的交点
        private static Tuple<double, double> FindIntersection(Tuple<double, double> p1, Tuple<double, double> p2, Tuple<double, double> p3, Tuple<double, double> p4)
        {
            double x1 = p1.Item1;
            double y1 = p1.Item2;
            double x2 = p2.Item1;
            double y2 = p2.Item2;
            double x3 = p3.Item1;
            double y3 = p3.Item2;
            double x4 = p4.Item1;
            double y4 = p4.Item2;

            double denominator = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4);

            if (Math.Abs(denominator) < double.Epsilon)
            {
                return null; // 平行或共线，无交点
            }

            double x = ((x1 * y2 - y1 * x2) * (x3 - x4) - (x1 - x2) * (x3 * y4 - y3 * x4)) / denominator;
            double y = ((x1 * y2 - y1 * x2) * (y3 - y4) - (y1 - y2) * (x3 * y4 - y3 * x4)) / denominator;

            return new Tuple<double, double>(x, y);
        }

        // 根据交点分割多边形集合
        public static List<List<Coordinate>> SplitPolygons(List<List<Coordinate>> polygons, List<Coordinate> intersectionPoints)
        {
            List<List<Coordinate>> splittedPolygons = new List<List<Coordinate>>();

            foreach (var polygon in polygons)
            {
                List<Coordinate> splittedPolygon = new List<Coordinate>(polygon);

                foreach (var intersectionPoint in intersectionPoints)
                {
                    if (IsInsidePolygon(intersectionPoint, polygon))
                    {
                        splittedPolygon.Add(intersectionPoint);
                    }
                }

                splittedPolygon = splittedPolygon.OrderBy(p => Math.Atan2(p.Y - intersectionPoints[0].Y, p.X - intersectionPoints[0].X)).ToList();
                splittedPolygons.Add(splittedPolygon);
            }

            return splittedPolygons;
        }

        // 判断点是否在多边形内部
        private static bool IsInsidePolygon(Coordinate point, List<Coordinate> polygon)
        {
            int count = 0;
            int n = polygon.Count;

            for (int i = 0; i < n; i++)
            {
                var p1 = polygon[i];
                var p2 = polygon[(i + 1) % n];

                if (IsPointOnSegment(point, p1, p2))
                {
                    return true; // 点在多边形的边上
                }

                if (point.Y > Math.Min(p1.Y, p2.Y) && point.Y <= Math.Max(p1.Y, p2.Y) && point.X <= Math.Max(p1.X, p2.X) && p1.Y != p2.Y)
                {
                    double xIntersection = (point.Y - p1.Y) * (p2.X - p1.X) / (p2.Y - p1.Y) + p1.X;
                    if (p1.X == p2.X || point.X <= xIntersection)
                    {
                        count++;
                    }
                }
            }

            return count % 2 == 1;
        }

        // 判断点是否在线段上
        private static bool IsPointOnSegment(Coordinate point, Coordinate p1, Coordinate p2)
        {
            return Math.Abs(Distance(point, p1) + Distance(point, p2) - Distance(p1, p2)) < double.Epsilon;
        }

        // 计算两个点之间的距离
        private static double Distance(Coordinate p1, Coordinate p2)
        {
            double dx = p1.X - p2.X;
            double dy = p1.Y - p2.Y;
            return Math.Sqrt(dx * dx + dy * dy);
        }
    }
}