From 1f84dcdeb24898a0c6eda719b66cd844bd4660ba Mon Sep 17 00:00:00 2001
From: nattthebear <goyuken@gmail.com>
Date: Sat, 22 Aug 2020 14:58:35 -0400
Subject: [PATCH] zwinder rewinder - fix all sorts of funsies when the state
 count cap is reached

---
 .../rewind/ZwinderBuffer.cs                   |  6 ++++++
 .../Movie/ZwinderStateManagerTests.cs         | 21 +++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs b/src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs
index 9f6a6c8685..9ee5c7e5de 100644
--- a/src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs
+++ b/src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs
@@ -136,6 +136,12 @@ namespace BizHawk.Client.Common
 			if (!force && !ShouldCapture(frame))
 				return;
 
+			if (Count == STATEMASK)
+			{
+				indexInvalidated?.Invoke(0);
+				_firstStateIndex = (_firstStateIndex + 1) & STATEMASK;
+			}
+
 			var start = (_states[HeadStateIndex].Start + _states[HeadStateIndex].Size) & _sizeMask;
 			var initialMaxSize = Count > 0
 					? (_states[_firstStateIndex].Start - start) & _sizeMask
diff --git a/src/BizHawk.Tests/Client.Common/Movie/ZwinderStateManagerTests.cs b/src/BizHawk.Tests/Client.Common/Movie/ZwinderStateManagerTests.cs
index 33849f090b..0333a9e1eb 100644
--- a/src/BizHawk.Tests/Client.Common/Movie/ZwinderStateManagerTests.cs
+++ b/src/BizHawk.Tests/Client.Common/Movie/ZwinderStateManagerTests.cs
@@ -25,6 +25,27 @@ namespace BizHawk.Tests.Client.Common.Movie
 			Assert.AreEqual(zw.Settings.RecentBufferSize, zw2.Settings.RecentBufferSize);
 		}
 
+		[TestMethod]
+		public void CountEvictWorks()
+		{
+			using var zb = new ZwinderBuffer(new RewindConfig
+			{
+				BufferSize = 1,
+				TargetFrameLength = 1
+			});
+			var ss = new StateSource
+			{
+				PaddingData = new byte[10]
+			};
+			var stateCount = 0;
+			for (int i = 0; i < 1000000; i++)
+			{
+				zb.Capture(i, s => ss.SaveStateBinary(new BinaryWriter(s)), j => stateCount--, true);
+				stateCount++;
+			}
+			Assert.AreEqual(zb.Count, stateCount);
+		}
+
 		[TestMethod]
 		public void SaveCreateBufferRoundTrip()
 		{