add rollback session client events

Author: lucasteles

src/Backdash/Core/ThrowIf.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.Globalization;
 using System.Runtime.CompilerServices;
 
@@ -26,6 +27,9 @@ public static void InvalidEnum<T>(
             throw new ArgumentOutOfRangeException($"Invalid Enum of type {typeof(T).Name} for {argName}: {value}");
     }
 
+    [Conditional("DEBUG")]
+    [Conditional("TRACE")]
+    [Conditional("TOOLS")]
     public static void Assert(
         bool condition,
         string? info = null,

src/Backdash/Session/Backends/SyncTestSession.cs

@@ -333,6 +333,7 @@ public void AdvanceFrame()
         synchronizer.LoadFrame(lastVerified);
 
         inRollback = true;
+        callbacks.BeginRollback(CurrentFrame);
         while (savedFrames.Count > 0)
         {
             callbacks.AdvanceFrame();
@@ -365,6 +366,7 @@ public void AdvanceFrame()
 
         lastVerified = frame;
         inRollback = false;
+        callbacks.EndRollback(CurrentFrame);
     }
 
     void HandleDesync(Frame frame, SavedFrameBytes current, SavedState previous)

src/Backdash/Session/INetcodeSessionHandler.cs

@@ -68,6 +68,16 @@ public interface INetcodeSessionHandler
     /// <seealso cref="IStateStringParser.GetStateString" />
     object? CreateState(Frame frame, ref readonly BinaryBufferReader reader) => null;
 
+    /// <summary>
+    ///     Notification that a rollback is started.
+    /// </summary>
+    void BeginRollback(Frame frame) { }
+
+    /// <summary>
+    ///     Notification that a rollback is ended.
+    /// </summary>
+    void EndRollback(Frame frame) { }
+
     /// <summary>
     ///     Called when a replay session run all inputs
     /// </summary>

src/Backdash/Synchronizing/Input/Synchronizer.cs

@@ -41,26 +41,23 @@ public Synchronizer(
         this.options = options;
         this.logger = logger;
         this.players = players;
-        this.Store = stateStore;
         this.checksumProvider = checksumProvider;
         this.localConnections = localConnections;
         this.inputComparer = inputComparer ?? EqualityComparer<TInput>.Default;
         this.checksumStore = checksumStore;
-
+        Store = stateStore;
         inputQueues = new(2);
         NumberSerializer = options.GetEndiannessNumberStateSerializer();
         var saveBufferSize = options.TotalSavedFramesAllowed;
         stateStore.Initialize(saveBufferSize);
     }
 
+    float rollbackFrameCounter;
+
     public bool InRollback { get; private set; }
     public IStateStore Store { get; }
     public EndiannessSerializer.INumberSerializer NumberSerializer { get; }
-
-    float rollbackFrameCounter;
-
     public Frame CurrentFrame => currentFrame;
-
     public Endianness SerializationEndianness => NumberSerializer.Endianness;
     public FrameSpan FramesBehind => new(currentFrame.Number - lastConfirmedFrame.Number);
     public FrameSpan RollbackFrames => new((int)Math.Round(rollbackFrameCounter));
@@ -187,6 +184,7 @@ public void AdjustSimulation(Frame seekTo)
         var rollbackCount = currentFrame.Number - seekTo.Number;
         logger.Write(LogLevel.Debug, $"Catching up. rolling back {rollbackCount} frames");
         InRollback = true;
+        Callbacks.BeginRollback(currentFrame);
 
         // Flush our input queue and load the last frame.
         LoadFrame(seekTo);
@@ -202,6 +200,7 @@ public void AdjustSimulation(Frame seekTo)
 
         ThrowIf.Assert(currentFrame == localCurrentFrame);
         InRollback = false;
+        Callbacks.EndRollback(currentFrame);
     }
 
     public bool TryLoadFrame(Frame frame)