feat: Implement server directory registration and user count tracking

src/EchoHub.Server/Services/PresenceTracker.cs

@@ -110,4 +110,9 @@ public class PresenceTracker
     {
         return _userConnections.TryGetValue(username, out var connections) && connections.Count > 0;
     }
+
+    public int GetOnlineUserCount()
+    {
+        return _userConnections.Count;
+    }
 }

src/EchoHub.Server/Services/ServerDirectoryService.cs

@@ -0,0 +1,139 @@
+using Microsoft.AspNetCore.SignalR.Client;
+
+namespace EchoHub.Server.Services;
+
+public sealed class ServerDirectoryService(
+    IConfiguration configuration,
+    PresenceTracker presenceTracker,
+    ILogger<ServerDirectoryService> logger) : BackgroundService
+{
+    private const string DirectoryHubUrl = "https://echohub.voidcube.cloud/hubs/servers";
+    private static readonly TimeSpan UpdateInterval = TimeSpan.FromSeconds(30);
+
+    private HubConnection? _connection;
+    private int _lastReportedUserCount = -1;
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        var isPublic = configuration.GetValue<bool>("Server:PublicServer");
+        if (!isPublic)
+        {
+            logger.LogInformation("PublicServer is disabled — not registering with directory");
+            return;
+        }
+
+        var host = configuration["Server:PublicHost"];
+        var port = configuration.GetValue<int>("Server:PublicPort");
+
+        if (string.IsNullOrWhiteSpace(host))
+        {
+            logger.LogWarning("PublicServer is enabled but Server:PublicHost is not set — skipping directory registration");
+            return;
+        }
+
+        if (port <= 0)
+        {
+            logger.LogWarning("PublicServer is enabled but Server:PublicPort is invalid — skipping directory registration");
+            return;
+        }
+
+        var serverName = configuration["Server:Name"] ?? "EchoHub Server";
+        var description = configuration["Server:Description"];
+
+        _connection = new HubConnectionBuilder()
+            .WithUrl(DirectoryHubUrl)
+            .WithAutomaticReconnect()
+            .Build();
+
+        _connection.Reconnected += async _ =>
+        {
+            logger.LogInformation("Reconnected to directory — re-registering server");
+            await RegisterAsync(serverName, description, host, port);
+        };
+
+        _connection.Closed += ex =>
+        {
+            if (ex is not null)
+                logger.LogWarning(ex, "Directory connection closed with error");
+            return Task.CompletedTask;
+        };
+
+        // Initial connection with retry
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                await _connection.StartAsync(stoppingToken);
+                logger.LogInformation("Connected to directory at {Url}", DirectoryHubUrl);
+                break;
+            }
+            catch (Exception ex)
+            {
+                logger.LogWarning(ex, "Failed to connect to directory — retrying in 30s");
+                await Task.Delay(UpdateInterval, stoppingToken);
+            }
+        }
+
+        if (stoppingToken.IsCancellationRequested)
+            return;
+
+        // Register on first connect
+        await RegisterAsync(serverName, description, host, port);
+
+        // Poll user count and send updates
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            await Task.Delay(UpdateInterval, stoppingToken);
+
+            if (_connection.State != HubConnectionState.Connected)
+                continue;
+
+            var currentCount = presenceTracker.GetOnlineUserCount();
+            if (currentCount == _lastReportedUserCount)
+                continue;
+
+            try
+            {
+                await _connection.InvokeAsync("UpdateUserCount", currentCount, stoppingToken);
+                _lastReportedUserCount = currentCount;
+                logger.LogDebug("Updated directory user count to {Count}", currentCount);
+            }
+            catch (Exception ex)
+            {
+                logger.LogWarning(ex, "Failed to update user count on directory");
+            }
+        }
+    }
+
+    private async Task RegisterAsync(string name, string? description, string host, int port)
+    {
+        if (_connection?.State != HubConnectionState.Connected)
+            return;
+
+        try
+        {
+            var userCount = presenceTracker.GetOnlineUserCount();
+            var dto = new RegisterServerDto(name, description, host, port, userCount);
+            await _connection.InvokeAsync("RegisterServer", dto);
+            _lastReportedUserCount = userCount;
+            logger.LogInformation("Registered with directory as {Name} at {Host}:{Port}", name, host, port);
+        }
+        catch (Exception ex)
+        {
+            logger.LogWarning(ex, "Failed to register with directory");
+        }
+    }
+
+    public override async Task StopAsync(CancellationToken cancellationToken)
+    {
+        if (_connection is not null)
+        {
+            await _connection.DisposeAsync();
+            _connection = null;
+        }
+
+        await base.StopAsync(cancellationToken);
+    }
+}
+
+internal record RegisterServerDto(string Name, string? Description, string Host, int Port, int UserCount);