deduplicate connection logic

tanks-backend/TanksServer/Interactivity/DroppablePackageRequestConnection.cs

@@ -0,0 +1,50 @@
+using System.Diagnostics;
+using DotNext.Threading;
+
+namespace TanksServer.Interactivity;
+
+internal abstract class DroppablePackageRequestConnection<TPackage>(
+    ILogger logger,
+    ByteChannelWebSocket socket
+) : WebsocketServerConnection(logger, socket), IDisposable
+    where TPackage : class, IDisposable
+{
+    private readonly AsyncAutoResetEvent _nextPackageEvent = new(false, 1);
+    private int _runningMessageHandlers = 0;
+    private TPackage? _next;
+
+    protected override ValueTask HandleMessageAsync(Memory<byte> _)
+    {
+        if (Interlocked.Increment(ref _runningMessageHandlers) == 1)
+            return Core();
+
+        // client has requested multiple frames, ignoring duplicate requests
+        Interlocked.Decrement(ref _runningMessageHandlers);
+        return ValueTask.CompletedTask;
+
+        async ValueTask Core()
+        {
+            await _nextPackageEvent.WaitAsync();
+            var package = Interlocked.Exchange(ref _next, null);
+            if (package == null)
+                throw new UnreachableException("package should be set here");
+            await SendPackageAsync(package);
+            Interlocked.Decrement(ref _runningMessageHandlers);
+        }
+    }
+
+    protected void SetNextPackage(TPackage next)
+    {
+        var oldNext = Interlocked.Exchange(ref _next, next);
+        _nextPackageEvent.Set();
+        oldNext?.Dispose();
+    }
+
+    protected abstract ValueTask SendPackageAsync(TPackage package);
+
+    public override void Dispose()
+    {
+        _nextPackageEvent.Dispose();
+        Interlocked.Exchange(ref _next, null)?.Dispose();
+    }
+}