From a9bca671d0e3ae2d4a14cf36e5ac541a78bbb63e Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Thu, 8 Oct 2020 17:17:52 +0900
Subject: [PATCH] Make component and add hooking events

---
 .../Edit/TransactionalCommitComponent.cs      | 32 +++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/osu.Game/Screens/Edit/TransactionalCommitComponent.cs b/osu.Game/Screens/Edit/TransactionalCommitComponent.cs
index 87a29a6237..3d3539ee2f 100644
--- a/osu.Game/Screens/Edit/TransactionalCommitComponent.cs
+++ b/osu.Game/Screens/Edit/TransactionalCommitComponent.cs
@@ -2,14 +2,30 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using osu.Framework.Graphics;
 
 namespace osu.Game.Screens.Edit
 {
     /// <summary>
     /// A component that tracks a batch change, only applying after all active changes are completed.
     /// </summary>
-    public abstract class TransactionalCommitComponent
+    public abstract class TransactionalCommitComponent : Component
     {
+        /// <summary>
+        /// Fires whenever a transaction begins. Will not fire on nested transactions.
+        /// </summary>
+        public event Action TransactionBegan;
+
+        /// <summary>
+        /// Fires when the last transaction completes.
+        /// </summary>
+        public event Action TransactionEnded;
+
+        /// <summary>
+        /// Fires when <see cref="SaveState"/> is called and results in a non-transactional state save.
+        /// </summary>
+        public event Action SaveStateTriggered;
+
         public bool TransactionActive => bulkChangesStarted > 0;
 
         private int bulkChangesStarted;
@@ -17,7 +33,11 @@ namespace osu.Game.Screens.Edit
         /// <summary>
         /// Signal the beginning of a change.
         /// </summary>
-        public void BeginChange() => bulkChangesStarted++;
+        public void BeginChange()
+        {
+            if (bulkChangesStarted++ == 0)
+                TransactionBegan?.Invoke();
+        }
 
         /// <summary>
         /// Signal the end of a change.
@@ -29,14 +49,22 @@ namespace osu.Game.Screens.Edit
                 throw new InvalidOperationException($"Cannot call {nameof(EndChange)} without a previous call to {nameof(BeginChange)}.");
 
             if (--bulkChangesStarted == 0)
+            {
                 UpdateState();
+                TransactionEnded?.Invoke();
+            }
         }
 
+        /// <summary>
+        /// Force an update of the state with no attached transaction.
+        /// This is a no-op if a transaction is already active. Should generally be used as a safety measure to ensure granular changes are not left outside a transaction.
+        /// </summary>
         public void SaveState()
         {
             if (bulkChangesStarted > 0)
                 return;
 
+            SaveStateTriggered?.Invoke();
             UpdateState();
         }