h-school/src/HSchool.Server/Net/ClientRegistry.cs

using System.Collections.Concurrent;
using System.Net.WebSockets;

namespace HSchool.Server.Net;

/// <summary>Tracks live connections and hands out client ids.</summary>
internal sealed class ClientRegistry
{
    private readonly ConcurrentDictionary<uint, GameClient> _clients = new();
    private readonly object _names = new();
    private uint _nextPlayerId;

    public int Count => _clients.Count;

    /// <summary>Snapshot-free enumeration; safe because the dictionary is concurrent.</summary>
    public IEnumerable<GameClient> All => _clients.Values;

    public GameClient Add(WebSocket socket)
    {
        var playerId = Interlocked.Increment(ref _nextPlayerId);
        var client = new GameClient(playerId, socket);
        _clients[playerId] = client;
        return client;
    }

    public GameClient? Find(uint playerId) => _clients.GetValueOrDefault(playerId);

    public void Remove(uint playerId) => _clients.TryRemove(playerId, out _);

    public bool IsUserNameOnline(string normalizedUserName)
    {
        lock (_names)
        {
            return HasUserName(normalizedUserName);
        }
    }

    /// <summary>
    /// One live socket per name. Checked under the same lock as <see cref="IsUserNameOnline"/>
    /// so a second tab cannot sneak a Welcome in between the HTTP check and SetUserName.
    /// </summary>
    public bool TryClaimUserName(GameClient client, string userName)
    {
        lock (_names)
        {
            if (HasUserName(userName))
            {
                return false;
            }

            client.SetUserName(userName);
            return true;
        }
    }

    private bool HasUserName(string normalizedUserName)
    {
        foreach (var existing in _clients.Values)
        {
            if (existing.UserName is null)
            {
                continue;
            }

            if (string.Equals(existing.NormalizedUserName, normalizedUserName, StringComparison.OrdinalIgnoreCase))
            {
                return true;
            }
        }

        return false;
    }
}