using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.DirectoryServices;
using System.Linq;
using System.Net;
using System.Net.NetworkInformation;
using System.Threading;
using System.Threading.Tasks;

public class NetworkScanner
{
    public class OnlinePC
    {
        public string Hostname { get; set; }
        public string IPAddress { get; set; }
    }

    public static async Task<List<OnlinePC>> GetOnlineDomainComputersAsync(int timeout = 1000, int maxParallel = 100)
    {
        var computers = GetAllDomainComputers();
        var onlinePCs = new ConcurrentBag<OnlinePC>();

        using (SemaphoreSlim semaphore = new SemaphoreSlim(maxParallel))
        {
            var tasks = computers.Select(async hostname =>
            {
                await semaphore.WaitAsync();

                try
                {
                    using (Ping ping = new Ping())
                    {
                        var reply = await ping.SendPingAsync(hostname, timeout);

                        if (reply.Status == IPStatus.Success)
                        {
                            string ip = reply.Address.ToString();

                            onlinePCs.Add(new OnlinePC
                            {
                                Hostname = hostname,
                                IPAddress = ip
                            });
                        }
                    }
                }
                catch
                {
                    // Ignore unreachable hosts
                }
                finally
                {
                    semaphore.Release();
                }
            });

            await Task.WhenAll(tasks);
        }

        return onlinePCs.ToList();
    }

    private static List<string> GetAllDomainComputers()
    {
        var list = new List<string>();

        using (DirectoryEntry entry = new DirectoryEntry())
        using (DirectorySearcher searcher = new DirectorySearcher(entry))
        {
            searcher.Filter = "(objectCategory=computer)";
            searcher.PropertiesToLoad.Add("name");

            foreach (SearchResult result in searcher.FindAll())
            {
                if (result.Properties.Contains("name"))
                {
                    list.Add(result.Properties["name"][0].ToString());
                }
            }
        }

        return list;
    }
}