From 618a8491bf4a06bfd242418fee2727bd0db5dfc5 Mon Sep 17 00:00:00 2001
From: Leon Friedrich <60421075+ElectroJr@users.noreply.github.com>
Date: Tue, 7 Nov 2023 15:07:26 +1100
Subject: [PATCH] Add `BeforeApplyState` event to replay playback (#4536)

---
 Robust.Client/Replays/Playback/IReplayPlaybackManager.cs  | 8 +++++++-
 .../Replays/Playback/ReplayPlaybackManager.Checkpoint.cs  | 1 +
 .../Replays/Playback/ReplayPlaybackManager.Time.cs        | 4 +++-
 .../Replays/Playback/ReplayPlaybackManager.Update.cs      | 4 +++-
 Robust.Client/Replays/Playback/ReplayPlaybackManager.cs   | 2 ++
 5 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/Robust.Client/Replays/Playback/IReplayPlaybackManager.cs b/Robust.Client/Replays/Playback/IReplayPlaybackManager.cs
index 3073bc754..3793f8140 100644
--- a/Robust.Client/Replays/Playback/IReplayPlaybackManager.cs
+++ b/Robust.Client/Replays/Playback/IReplayPlaybackManager.cs
@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using Robust.Shared.GameObjects;
+using Robust.Shared.GameStates;
 using Robust.Shared.Network;
 using Robust.Shared.Replays;
 using Robust.Shared.Serialization.Markdown.Mapping;
@@ -128,6 +129,11 @@ public interface IReplayPlaybackManager
     /// </summary>
     event Action? ReplayUnpaused;
 
+    /// <summary>
+    /// Invoked just before a replay applies a game state.
+    /// </summary>
+    event Action<(GameState Current, GameState? Next)>? BeforeApplyState;
+
     /// <summary>
     /// If currently replaying a client-side recording, this is the user that recorded the replay.
     /// Useful for setting default observer spawn positions.
@@ -137,5 +143,5 @@ public interface IReplayPlaybackManager
     /// <summary>
     /// Fetches the entity that the <see cref="Recorder"/> is currently attached to.
     /// </summary>
-    public bool TryGetRecorderEntity([NotNullWhen(true)] out EntityUid? uid);
+    bool TryGetRecorderEntity([NotNullWhen(true)] out EntityUid? uid);
 }
diff --git a/Robust.Client/Replays/Playback/ReplayPlaybackManager.Checkpoint.cs b/Robust.Client/Replays/Playback/ReplayPlaybackManager.Checkpoint.cs
index cfd9f77e0..adc8ed124 100644
--- a/Robust.Client/Replays/Playback/ReplayPlaybackManager.Checkpoint.cs
+++ b/Robust.Client/Replays/Playback/ReplayPlaybackManager.Checkpoint.cs
@@ -66,6 +66,7 @@ internal sealed partial class ReplayPlaybackManager
         _gameState.ClearDetachQueue();
         EnsureDetachedExist(checkpoint);
         _gameState.DetachImmediate(checkpoint.Detached);
+        BeforeApplyState?.Invoke((checkpoint.State, next));
         _gameState.ApplyGameState(checkpoint.State, next);
     }
 
diff --git a/Robust.Client/Replays/Playback/ReplayPlaybackManager.Time.cs b/Robust.Client/Replays/Playback/ReplayPlaybackManager.Time.cs
index 8be336320..9643ae1ac 100644
--- a/Robust.Client/Replays/Playback/ReplayPlaybackManager.Time.cs
+++ b/Robust.Client/Replays/Playback/ReplayPlaybackManager.Time.cs
@@ -63,7 +63,9 @@ internal sealed partial class ReplayPlaybackManager
             // Clear existing lerps
             _entMan.EntitySysManager.GetEntitySystem<TransformSystem>().Reset();
 
-            _gameState.ApplyGameState(state, Replay.NextState);
+            var next = Replay.NextState;
+            BeforeApplyState?.Invoke((state, next));
+            _gameState.ApplyGameState(state, next);
             ProcessMessages(Replay.CurMessages, skipEffectEvents);
 
             // TODO REPLAYS block audio
diff --git a/Robust.Client/Replays/Playback/ReplayPlaybackManager.Update.cs b/Robust.Client/Replays/Playback/ReplayPlaybackManager.Update.cs
index b14a36b36..6fb60f36e 100644
--- a/Robust.Client/Replays/Playback/ReplayPlaybackManager.Update.cs
+++ b/Robust.Client/Replays/Playback/ReplayPlaybackManager.Update.cs
@@ -42,7 +42,9 @@ internal sealed partial class ReplayPlaybackManager
         {
             var state = Replay.CurState;
             _gameState.UpdateFullRep(state, cloneDelta: true);
-            _gameState.ApplyGameState(state, Replay.NextState);
+            var next = Replay.NextState;
+            BeforeApplyState?.Invoke((state, next));
+            _gameState.ApplyGameState(state, next);
             DebugTools.Assert(Replay.LastApplied >= state.FromSequence);
             DebugTools.Assert(Replay.LastApplied + 1 <= state.ToSequence);
             Replay.LastApplied = state.ToSequence;
diff --git a/Robust.Client/Replays/Playback/ReplayPlaybackManager.cs b/Robust.Client/Replays/Playback/ReplayPlaybackManager.cs
index 22f9f1a24..a8df7fe91 100644
--- a/Robust.Client/Replays/Playback/ReplayPlaybackManager.cs
+++ b/Robust.Client/Replays/Playback/ReplayPlaybackManager.cs
@@ -12,6 +12,7 @@ using Robust.Client.Upload;
 using Robust.Shared;
 using Robust.Shared.Configuration;
 using Robust.Shared.GameObjects;
+using Robust.Shared.GameStates;
 using Robust.Shared.IoC;
 using Robust.Shared.Log;
 using Robust.Shared.Network;
@@ -44,6 +45,7 @@ internal sealed partial class ReplayPlaybackManager : IReplayPlaybackManager
     public event Action? ReplayPlaybackStopped;
     public event Action? ReplayPaused;
     public event Action? ReplayUnpaused;
+    public event Action<(GameState Current, GameState? Next)>? BeforeApplyState;
 
     public ReplayData? Replay { get; private set; }
     public NetUserId? Recorder => Replay?.Recorder;