using System;

using System.Collections.Generic;

using System.Configuration;

using System.Linq;

using System.Net;

using System.Diagnostics;

using System.IO;

using System.Threading;

​

    class Program

    {

        private const int ApiLimit = 10;

        static void Main(string[] args)

        {

            var apiRequestCount = 20;

​

            for(int i = 0; i < apiRequestCount; i++)

            {

                PrintTime();

            }

        }

        private static int count = 0;    

        private static void PrintTime()

        {

            EnforceRateLimit();

            Console.WriteLine($"[{FormatTimestamp(DateTime.Now)}]: Request #{++count}");

        }

        private static List<DateTime> requests = new List<DateTime>();

        private static object _requestLimitLock = new object();

        private static void EnforceRateLimit()

        {

            lock (_requestLimitLock)

            { 

                var ratedRequests = requests.Where(item => (DateTime.Now - item).TotalMilliseconds <= 1000).ToList();

                if (ratedRequests.Count >= ApiLimit)

                {

                    // get time since the oldest request within the last 1000, eg: 600ms

                    var timeSinceOldestRequest = (DateTime.Now - ratedRequests.First()).TotalMilliseconds;

​

                    // compute time to wait, eg:400ms

                    var timeToWait = 1000 - timeSinceOldestRequest;

​

                    Console.WriteLine($"\n[{FormatTimestamp(DateTime.Now)}]: waiting {timeToWait:N2}ms, until {FormatTimestamp(DateTime.Now.AddMilliseconds(timeToWait))}\n");

​

                    // wait the 400ms

                    Thread.Sleep((int)timeToWait);

                }

​

​

                // add the current request to the list

                requests.Add(DateTime.Now);

​

                //clear all requests older than 2000ms

                requests.RemoveAll(item => (DateTime.Now - item).TotalMilliseconds > 2000);

            }

        }

​

​

​

        private static string FormatTimestamp(DateTime time)

        {

            return $"{time.Minute}:{time.Second}:{time.Millisecond}";

        }

​

​

}