From f113b201885a6a64321391a278b684a6902c9ea5 Mon Sep 17 00:00:00 2001
From: Yifeng Wang <i@ewind.us>
Date: Sat, 25 Dec 2021 23:37:10 +0800
Subject: [PATCH] fix continuous paired undo redo of arbitrary length

---
 src/structs/Item.js      | 15 +++++++++++++--
 tests/undo-redo.tests.js | 24 ++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/src/structs/Item.js b/src/structs/Item.js
index 656f5e5b..79f800ae 100644
--- a/src/structs/Item.js
+++ b/src/structs/Item.js
@@ -210,10 +210,21 @@ export const redoItem = (transaction, item, redoitems, itemsToDelete) => {
       }
       right = right.right
     }
+
+    /**
+     * @type {Item|null}
+     */
+    let leftTrace = left
     // Iterate right while right is in itemsToDelete
     // If it is intended to delete right while item is redone, we can expect that item should replace right.
-    while (left !== null && left.right !== null && left.right !== right && itemsToDelete.findIndex(d => d === /** @type {Item} */ (left).right) >= 0) {
-      left = left.right
+    while (leftTrace !== null && leftTrace.right !== null && leftTrace.right !== right) {
+      if (itemsToDelete.findIndex(d => d === /** @type {Item} */ leftTrace) >= 0) {
+        break
+      }
+      leftTrace = leftTrace.right
+    }
+    if (leftTrace !== null) {
+      left = leftTrace
     }
   }
   const nextClock = getState(store, ownClientID)
diff --git a/tests/undo-redo.tests.js b/tests/undo-redo.tests.js
index 991225ca..c29c5a52 100644
--- a/tests/undo-redo.tests.js
+++ b/tests/undo-redo.tests.js
@@ -358,6 +358,26 @@ export const testUndoNestedUndoIssue = tc => {
     text.set('blocks', blocks3block)
   })
 
+  const blocks4 = new Y.Array()
+  const blocks4block = new Y.Map()
+  doc.transact(() => {
+    blocks4block.set('text', 'Something Else 2')
+    blocks4.push([blocks4block])
+    text.set('blocks', blocks4block)
+  })
+
+  const blocks5 = new Y.Array()
+  const blocks5block = new Y.Map()
+  doc.transact(() => {
+    blocks5block.set('text', 'Something Else 3')
+    blocks5.push([blocks5block])
+    text.set('blocks', blocks5block)
+  })
+
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else 3' } } })
+  undoManager.undo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else 2' } } })
+  undoManager.undo()
   t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else' } } })
   undoManager.undo()
   t.compare(design.toJSON(), { text: { blocks: { text: 'Something' } } })
@@ -371,4 +391,8 @@ export const testUndoNestedUndoIssue = tc => {
   t.compare(design.toJSON(), { text: { blocks: { text: 'Something' } } })
   undoManager.redo()
   t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else' } } })
+  undoManager.redo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else 2' } } })
+  undoManager.redo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else 3' } } })
 }