resume token demo for watcher/change-stream

Program.cs

using MongoDB.Bson;
using MongoDB.Entities;
using System;
using System.IO;
using System.Threading.Tasks;

namespace TestApplication
{
    public class Book : Entity
    {
        public string Title { get; set; }
    }

    public static class Program
    {
        private static async Task Main()
        {
            await DB.InitAsync("test");

            var watcher = DB.Watcher<Book>("book-watcher");

            watcher.OnChanges += books =>
            {
                foreach (var book in books)
                {
                    Console.WriteLine($"received: {book.Title}");
                }
            };

            if (File.Exists("resume.token"))
            {
                var resumeToken = BsonDocument.Parse(File.ReadAllText("resume.token"));
                watcher.StartWithToken(resumeToken, EventType.Created, batchSize: 10);
            }
            else
            {
                watcher.Start(EventType.Created, batchSize: 10);
                for (int i = 1; i <= 20; i++)
                {
                    await new Book { Title = $"book {i}" }.SaveAsync();
                    await Task.Delay(500);
                    if (i == 10)
                    {
                        File.WriteAllText("resume.token", watcher.ResumeToken.ToJson());
                    }
                }
            }

            Console.WriteLine("press any key to exit...");
            Console.ReadLine();
        }

    }
}