Fix Overleaf file tree sync updates

1 files changed, 41 insertions, 5 deletions

diff --git a/src/main/otClient.ts b/src/main/otClient.ts
index 2917bcc..9d373bd 100644
--- a/src/main/otClient.ts
+++ b/src/main/otClient.ts
@@ -25,10 +25,16 @@ interface OtState {
   version: number
 }
 
+interface QueuedRemoteUpdate {
+  ops: OtOp[]
+  version: number
+}
+
 export class OtClient {
   private state: OtState
   private sendFn: SendFn
   private applyFn: ApplyFn
+  private queuedRemoteUpdates: QueuedRemoteUpdate[] = []
 
   constructor(version: number, sendFn: SendFn, applyFn: ApplyFn) {
     this.state = { name: 'synchronized', inflight: null, buffer: null, version }
@@ -115,6 +121,8 @@ export class OtClient {
         // to synchronized, the second arrives when we're already there.
         break
     }
+
+    this.processQueuedRemoteUpdates()
   }
 
   /**
@@ -122,15 +130,27 @@ export class OtClient {
    * Transform against inflight/buffered ops before applying.
    */
   onRemoteOps(ops: OtOp[], newVersion: number) {
-    // Stale message detection (matching Overleaf's ShareJS):
-    // if the server version is behind our version, we already processed this.
+    // ShareJS update.v is the document version before the op is applied.
+    // Drop duplicates and queue out-of-order messages until their base version
+    // catches up, matching Overleaf's in-order processing.
     if (newVersion < this.state.version) {
       return
     }
+    if (newVersion > this.state.version) {
+      this.queueRemoteUpdate(ops, newVersion)
+      return
+    }
+
+    this.applyRemoteOps(ops, newVersion)
+    this.processQueuedRemoteUpdates()
+  }
+
+  private applyRemoteOps(ops: OtOp[], newVersion: number) {
+    const nextVersion = newVersion + 1
 
     switch (this.state.name) {
       case 'synchronized':
-        this.state = { ...this.state, version: newVersion }
+        this.state = { ...this.state, version: nextVersion }
         this.applyFn(ops)
         break
 
@@ -139,7 +159,7 @@ export class OtClient {
         this.state = {
           ...this.state,
           inflight: transformedInflight,
-          version: newVersion
+          version: nextVersion
         }
         this.applyFn(transformedRemote)
         break
@@ -152,7 +172,7 @@ export class OtClient {
           ...this.state,
           inflight: inflightAfterRemote,
           buffer: bufferAfterRemote,
-          version: newVersion
+          version: nextVersion
         }
         this.applyFn(remoteAfterBuffer)
         break
@@ -160,7 +180,23 @@ export class OtClient {
     }
   }
 
+  private queueRemoteUpdate(ops: OtOp[], version: number) {
+    if (this.queuedRemoteUpdates.some((update) => update.version === version)) return
+    this.queuedRemoteUpdates.push({ ops, version })
+    this.queuedRemoteUpdates.sort((a, b) => a.version - b.version)
+  }
+
+  private processQueuedRemoteUpdates() {
+    let nextIndex = this.queuedRemoteUpdates.findIndex((update) => update.version === this.state.version)
+    while (nextIndex !== -1) {
+      const [next] = this.queuedRemoteUpdates.splice(nextIndex, 1)
+      this.applyRemoteOps(next.ops, next.version)
+      nextIndex = this.queuedRemoteUpdates.findIndex((update) => update.version === this.state.version)
+    }
+  }
+
   reset(version: number) {
     this.state = { name: 'synchronized', inflight: null, buffer: null, version }
+    this.queuedRemoteUpdates = []
   }
 }