fix load state before last input

Author: lucasteles

src/Backdash/Data/CircularBuffer.cs

@@ -61,7 +61,6 @@ T DropLast()
         return value;
     }
 
-
     public ref T Next() => ref array[head];
     public ref T Front() => ref array[CurrentIndex];
     public ref T Back() => ref array[tail];

src/Backdash/Frame.cs

@@ -102,7 +102,7 @@ public bool TryFormat(
     }
 
     /// <inheritdoc cref="Number" />
-    public static explicit operator int(Frame frame) => frame.Number;
+    public static implicit operator int(Frame frame) => frame.Number;
 
     /// <inheritdoc cref="Frame(int)" />
     public static explicit operator Frame(int frame) => new(frame);

src/Backdash/Session/Backends/LocalSession.cs

@@ -208,7 +208,7 @@ public void AdvanceFrame()
 
     public bool LoadFrame(Frame frame)
     {
-        frame = Frame.Max(in frame, in Frame.Zero);
+        if (frame.Number < 1) return false;
 
         if (frame.Number == CurrentFrame.Number)
         {

src/Backdash/Session/Backends/RemoteSession.cs

@@ -441,7 +441,7 @@ public void SetFrameDelay(NetcodePlayer player, int delayInFrames)
 
     public bool LoadFrame(Frame frame)
     {
-        frame = Frame.Max(in frame, in Frame.Zero);
+        if (frame.Number < 0) return false;
         return synchronizer.TryLoadFrame(in frame);
     }
 

src/Backdash/Session/Backends/ReplaySession.cs

@@ -207,7 +207,7 @@ public void SaveCurrentFrame()
 
     public bool LoadFrame(Frame frame)
     {
-        frame = Frame.Max(in frame, in Frame.Zero);
+        if (frame.Number < 0) return false;
 
         if (frame.Number == CurrentFrame.Number)
         {

src/Backdash/Session/Backends/SpectatorSession.cs

@@ -355,7 +355,7 @@ void SaveCurrentFrame()
 
     public bool LoadFrame(Frame frame)
     {
-        frame = Frame.Max(in frame, in Frame.Zero);
+        if (frame.Number < 0) return false;
 
         if (frame.Number == CurrentFrame.Number)
         {

src/Backdash/Session/Backends/SyncTestSession.cs

@@ -268,7 +268,7 @@ public ResultCode SynchronizeInputs()
 
     public bool LoadFrame(Frame frame)
     {
-        frame = Frame.Max(in frame, in Frame.Zero);
+        if (frame.Number < 0) return false;
         return synchronizer.TryLoadFrame(in frame);
     }
 

src/Backdash/Synchronizing/Input/InputQueue.cs

@@ -79,11 +79,19 @@ public void DiscardInputsAfter(in Frame frame)
 
         var offset = lastUserAddedFrame.Number - frame.Number;
         if (offset < 0) return;
+
         logger.Write(LogLevel.Debug, $"Queue {QueueId} => dropping last {offset} frames.");
         inputs.Advance(-offset);
+
         lastUserAddedFrame = frame;
         lastFrameRequested = frame;
         lastAddedFrame = frame + LocalFrameDelay;
+
+        if (!inputs.IsEmpty) return;
+        var firstInput = inputs.Front();
+        firstInput.Frame = frame;
+        lastAddedFrame = frame;
+        inputs.Add(firstInput);
     }
 
     public bool GetConfirmedInput(in Frame requestedFrame, ref GameInput<TInput> input)
@@ -101,13 +109,20 @@ public bool GetConfirmedInput(in Frame requestedFrame, ref GameInput<TInput> inp
 
     public bool GetInput(in Frame requestedFrame, out GameInput<TInput> input)
     {
+        if (inputs.IsEmpty)
+            throw new InvalidOperationException("Can't get inputs: queue is empty.");
+
         logger.Write(LogLevel.Trace, $"Queue {QueueId} => requesting input frame {requestedFrame.Number}.");
         // No one should ever try to grab any input when we have a prediction error.
         // Doing so means that we're just going further down the wrong path.
         ThrowIf.Assert(firstIncorrectFrame.IsNull);
         // Remember the last requested frame number for later. We'll need this in AddInput() to drop out of prediction mode.
         lastFrameRequested = requestedFrame;
-        ThrowIf.Assert(requestedFrame.Number >= FirstInput.Frame.Number);
+        if (requestedFrame.Number < FirstInput.Frame.Number)
+            throw new InvalidOperationException(
+                $"Requested frame ({requestedFrame.Number}) can not be smaller than the first input frame ({FirstInput.Frame.Number})."
+            );
+
         if (prediction.Frame.IsNull)
         {
             // If the frame requested is in our range, fetch it out of the queue and  return it.