Handle local changes correctly when receiving snapshot

src/document/document.ts

@@ -1072,6 +1072,14 @@ export class Document<T, P extends Indexable = Indexable> {
       this.localChanges.shift();
     }
 
+    // NOTE(hackerwins): If the document has local changes, we need to apply
+    // them after applying the snapshot. We need to treat the local changes
+    // as remote changes because the application should apply the local
+    // changes to their own document.
+    if (pack.hasSnapshot()) {
+      this.applyChanges(this.localChanges, OpSource.Remote);
+    }
+
     // 03. Update the checkpoint.
     this.checkpoint = this.checkpoint.forward(pack.getCheckpoint());
 

test/integration/client_test.ts

@@ -838,4 +838,29 @@ describe.sequential('Client', function () {
 
     vi.unstubAllGlobals();
   });
+
+  it('Should handle local changes correctly when receiving snapshot', async ({
+    task,
+  }) => {
+    type TestDoc = { counter: Counter };
+    await withTwoClientsAndDocuments<TestDoc>(async (c1, d1, c2, d2) => {
+      d1.update((r) => (r.counter = new Counter(yorkie.IntType, 0)));
+      await c1.sync();
+      await c2.sync();
+
+      // 01. c1 increases the counter for creating snapshot.
+      for (let i = 0; i < 500; i++) {
+        d1.update((r) => r.counter.increase(1));
+      }
+      await c1.sync();
+
+      // 02. c2 receives the snapshot and increases the counter simultaneously.
+      c2.sync();
+      d2.update((r) => r.counter.increase(1));
+
+      await c2.sync();
+      await c1.sync();
+      assert.equal(d1.toSortedJSON(), d2.toSortedJSON());
+    }, task.name);
+  });
 });

test/integration/snapshot_test.ts

@@ -38,8 +38,8 @@ describe('Snapshot', function () {
       await c1.sync();
       await c2.sync();
 
-      // 01. Updates 700 changes over snapshot threshold by c1.
-      for (let idx = 0; idx < 700; idx++) {
+      // 01. Updates 500 changes over snapshot threshold by c1.
+      for (let idx = 0; idx < 500; idx++) {
         d1.update((root) => {
           root.k1.edit(idx, idx, 'x');
         });