using System;

using System.IO;

using System.Net.Http;

using System.Threading.Tasks;

​

namespace ProofOfTime

{

    public class TimestampLogger

    {

        private readonly string _timestampFile = "validation_timestamp.txt";

​

        public DateTime StartTime { get; set; }

        public DateTime EndTime { get; set; }

​

        public void Start()

        {

            // Record the start time

            StartTime = DateTime.UtcNow;

            // Log to a file for verification

            File.WriteAllText(_timestampFile, $"Start: {StartTime}");

        }

​

        public async void Stop()

        {

            // Record the end time

            EndTime = DateTime.UtcNow;

​

            // Verify external timestamp

            await ValidateExternalTimestamp();

​

            // Log to a file for verification

            if (File.Exists(_timestampFile))

            {

                var existingContent = File.ReadAllText(_timestampFile);

                File.WriteAllText(_timestampFile, $"{existingContent}\nEnd: {EndTime}");

            }

        }

​

        private async Task ValidateExternalTimestamp(string api = "https://api.example.com/timestamp")

        {

            // Simple example of external timestamp verification

            using (var httpClient = new HttpClient())

            {

                try

                {

                    var response = await httpClient.GetAsync(api);

                    if (response.IsSuccessStatusCode)

                    {

                        var serverTime = await response.Content.ReadAsStringAsync();

                        // Compare with local time to detect discrepancies

                        var difference = DateTime.UtcNow - DateTime.Parse(serverTime);

                        if (difference.TotalSeconds > 5)

                        {

                            throw new Exception("Timestamp discrepancy detected.");

                        }

                    }

                }

                catch (Exception ex)

                {

                    throw new Exception($"Failed to validate timestamp: {ex.Message}", ex);

                }

            }

        }

​

        public bool VerifyTimeElapsed()

        {

            // Check if end time is after start time

            return EndTime > StartTime;

        }

    }

}