using System;

using System.Collections.Generic;

using System.IO;

using System.Linq;

using NetTopologySuite.Geometries;

using NetTopologySuite.IO;

using Newtonsoft.Json;

​

public class Program

{

    private static readonly PrecisionModel DefaultPrecisionModel = new(1000000.0);

    private static readonly GeometryFactory DefaultGeometryFactory = new GeometryFactoryEx(DefaultPrecisionModel, 4326)

    {OrientationOfExteriorRing = LinearRingOrientation.CounterClockwise};

    private static readonly JsonSerializer Serializer = GeoJsonSerializer.Create(new JsonSerializerSettings{Formatting = Formatting.Indented}, DefaultGeometryFactory);

    public static void Main()

    {

        var coordinates = new List<Coordinate>();

        Console.WriteLine("Build a Polygon: Enter at least four non-intersecting points to create a GeoJSON polygon.");

        string input;

        do

        {

            Console.WriteLine("Enter a latitude and longitude pair separated by a comma and a space " + "(example: -90, 180; enter nothing to build the polygon or q to quit without building the polygon): ");

            input = Console.ReadLine();

            if (string.IsNullOrWhiteSpace(input))

            {

                continue;

            }

​

            if ("q".Equals(input, StringComparison.InvariantCultureIgnoreCase))

            {

                Console.WriteLine("Exiting.");

                return;

            }

​

            var rawCoordinates = input.Trim().Split(", ");

            if (rawCoordinates.Length != 2)

            {

                Console.WriteLine("Both a latitude and a longitude must be supplied. Try again.");

                continue;

            }

​

            var latitudeResult = double.TryParse(rawCoordinates[0], out var latitude);

            if (!latitudeResult)

            {

                Console.WriteLine("Latitude was not a number. Try again.");

                continue;

            }

​

            var longitudeResult = double.TryParse(rawCoordinates[1], out var longitude);

            if (!longitudeResult)

            {

                Console.WriteLine("Longitude was not a number. Try again.");

                continue;

            }

​

            if (!TryAddCoordinate(longitude, latitude, out var result))

            {

                continue;

            }

​

            coordinates.Add(result);

        }

        while (!string.IsNullOrWhiteSpace(input));

        if (coordinates.Count < 4)

        {

            Console.WriteLine("Not enough points to create a polygon, exiting.");

            return;

        }

​

        if (!coordinates.First().Equals(coordinates.Last()))

        {

            Console.WriteLine("Coordinates do not form a closed ring. Will attempt to close them automagically.");

            coordinates.Add(coordinates.First());

        }

​

        var geom = DefaultGeometryFactory.CreatePolygon(coordinates.ToArray());

        if (!geom.IsValid)

        {

            Console.WriteLine("Resulting polygon was not valid. The points may be intersecting.");

            return;

        }

​

        Console.WriteLine("Polygon is correct (probably); writing it out to the console.");

        using (var stringWriter = new StringWriter())

            using (var jsonWriter = new JsonTextWriter(stringWriter))

            {

                Serializer.Serialize(jsonWriter, geom);

                Console.WriteLine(stringWriter.ToString());

            }

    }

​

    static bool TryAddCoordinate(double longitude, double latitude, out Coordinate coordinate)

    {

        coordinate = null;

        if (longitude is> 180.0 or < -180.0)

        {

            Console.WriteLine($"Longitude is outside of the [-180, 180] range (value: {longitude}).");

            return false;

        }

​

        if (latitude is> 90.0 or < -90.0)

        {

            Console.WriteLine($"Latitude is outside of the [-90, 90] range (value: {longitude}).");

            return false;

        }

​

        coordinate = new Coordinate(longitude, latitude);

        return true;

    }

}