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

namespace ConsoleApplication1
{
    public class StreetPoint
    {
        public StreetPoint(double _lng, double _lat)
        {
            lng = _lng;
            lat = _lat;
        }
        public double lng { get; set; }
        public double lat { get; set; }
    }
    public class GpsPolygonHelper
    {
        /// <summary>
        /// 坐标点是否在多边形内判断
        /// </summary>
        /// <param name="point"></param>
        /// <param name="pts"></param>
        /// <returns></returns>
        public static bool isPointInPolygon(StreetPoint point, List<StreetPoint> pts)
        {
            //检查类型
            if (point == null || pts == null)
                return false;

            var N = pts.Count;
            var boundOrVertex = true; //如果点位于多边形的顶点或边上，也算做点在多边形内，直接返回true
            var intersectCount = 0; //cross points count of x 
            double precision = 2e-10; //浮点类型计算时候与0比较时候的容差
            StreetPoint p1, p2; //neighbour bound vertices
            var p = point; //测试点
            p1 = pts[0]; //left vertex        
            for (var i = 1; i <= N; ++i)
            {
                //check all rays            
                if (p.lat.Equals(p1.lat) && p.lng.Equals(p1.lng))
                {
                    return boundOrVertex; //p is an vertex
                }

                p2 = pts[i % N]; //right vertex            
                if (p.lat < Math.Min(p1.lat, p2.lat) || p.lat > Math.Max(p1.lat, p2.lat))
                {
                    //ray is outside of our interests                
                    p1 = p2;
                    continue; //next ray left point
                }

                if (p.lat > Math.Min(p1.lat, p2.lat) && p.lat < Math.Max(p1.lat, p2.lat))
                {
                    //ray is crossing over by the algorithm (common part of)
                    if (p.lng <= Math.Max(p1.lng, p2.lng))
                    {
                        //x is before of ray                    
                        if (p1.lat == p2.lat && p.lng >= Math.Min(p1.lng, p2.lng))
                        {
                            //overlies on a horizontal ray
                            return boundOrVertex;
                        }

                        if (p1.lng == p2.lng)
                        {
                            //ray is vertical                        
                            if (p1.lng == p.lng)
                            {
                                //overlies on a vertical ray
                                return boundOrVertex;
                            }
                            else
                            {
                                //before ray
                                ++intersectCount;
                            }
                        }
                        else
                        {
                            //cross point on the left side                        
                            var xinters =
                                (p.lat - p1.lat) * (p2.lng - p1.lng) / (p2.lat - p1.lat) +
                                p1.lng; //cross point of lng                        
                            if (Convert.ToDouble(Math.Abs(p.lng - xinters)) < precision)
                            {
                                //overlies on a ray
                                return boundOrVertex;
                            }

                            if (p.lng < xinters)
                            {
                                //before ray
                                ++intersectCount;
                            }
                        }
                    }
                }
                else
                {
                    //special case when ray is crossing through the vertex                
                    if (p.lat == p2.lat && p.lng <= p2.lng)
                    {
                        //p crossing over p2                    
                        var p3 = pts[(i + 1) % N]; //next vertex                    
                        if (p.lat >= Math.Min(p1.lat, p3.lat) && p.lat <= Math.Max(p1.lat, p3.lat))
                        {
                            //p.lat lies between p1.lat & p3.lat
                            ++intersectCount;
                        }
                        else
                        {
                            intersectCount += 2;
                        }
                    }
                }
                p1 = p2; //next ray left point
            }

            if (intersectCount % 2 == 0)
            {
                //偶数在多边形外
                return false;
            }
            else
            {
                //奇数在多边形内
                return true;
            }

        }
    }
}