feat: fix delta apply to issues (#9830)

packages/element/src/delta.ts

@@ -151,6 +151,16 @@ export class Delta<T> {
     );
   }
 
+  /**
+   * Merges two deltas into a new one.
+   */
+  public static merge<T>(delta1: Delta<T>, delta2: Delta<T>) {
+    return Delta.create(
+      { ...delta1.deleted, ...delta2.deleted },
+      { ...delta1.inserted, ...delta2.inserted },
+    );
+  }
+
   /**
    * Merges deleted and inserted object partials.
    */
@@ -497,6 +507,11 @@ export interface DeltaContainer<T> {
    */
   applyTo(previous: T, ...options: unknown[]): [T, boolean];
 
+  /**
+   * Squashes the current delta with the given one.
+   */
+  squash(delta: DeltaContainer<T>): this;
+
   /**
    * Checks whether all `Delta`s are empty.
    */
@@ -504,7 +519,7 @@ export interface DeltaContainer<T> {
 }
 
 export class AppStateDelta implements DeltaContainer<AppState> {
-  private constructor(public readonly delta: Delta<ObservedAppState>) {}
+  private constructor(public delta: Delta<ObservedAppState>) {}
 
   public static calculate<T extends ObservedAppState>(
     prevAppState: T,
@@ -535,6 +550,11 @@ export class AppStateDelta implements DeltaContainer<AppState> {
     return new AppStateDelta(inversedDelta);
   }
 
+  public squash(delta: AppStateDelta): this {
+    this.delta = Delta.merge(this.delta, delta.delta);
+    return this;
+  }
+
   public applyTo(
     appState: AppState,
     nextElements: SceneElementsMap,
@@ -1196,8 +1216,8 @@ export class ElementsDelta implements DeltaContainer<SceneElementsMap> {
     const inverseInternal = (deltas: Record<string, Delta<ElementPartial>>) => {
       const inversedDeltas: Record<string, Delta<ElementPartial>> = {};
 
-      for (const [id, delta] of Object.entries(deltas)) {
-        inversedDeltas[id] = Delta.create(delta.inserted, delta.deleted);
+      for (const [id, { inserted, deleted }] of Object.entries(deltas)) {
+        inversedDeltas[id] = Delta.create({ ...inserted }, { ...deleted });
       }
 
       return inversedDeltas;
@@ -1395,6 +1415,42 @@ export class ElementsDelta implements DeltaContainer<SceneElementsMap> {
     }
   }
 
+  public squash(delta: ElementsDelta): this {
+    const { added, removed, updated } = delta;
+
+    for (const [id, nextDelta] of Object.entries(added)) {
+      const prevDelta = this.added[id];
+
+      if (!prevDelta) {
+        this.added[id] = nextDelta;
+      } else {
+        this.added[id] = Delta.merge(prevDelta, nextDelta);
+      }
+    }
+
+    for (const [id, nextDelta] of Object.entries(removed)) {
+      const prevDelta = this.removed[id];
+
+      if (!prevDelta) {
+        this.removed[id] = nextDelta;
+      } else {
+        this.removed[id] = Delta.merge(prevDelta, nextDelta);
+      }
+    }
+
+    for (const [id, nextDelta] of Object.entries(updated)) {
+      const prevDelta = this.updated[id];
+
+      if (!prevDelta) {
+        this.updated[id] = nextDelta;
+      } else {
+        this.updated[id] = Delta.merge(prevDelta, nextDelta);
+      }
+    }
+
+    return this;
+  }
+
   private static createApplier =
     (
       nextElements: SceneElementsMap,
@@ -1624,25 +1680,12 @@ export class ElementsDelta implements DeltaContainer<SceneElementsMap> {
       Array.from(prevElements).filter(([id]) => nextAffectedElements.has(id)),
     );
 
-    // calculate complete deltas for affected elements, and assign them back to all the deltas
-    // technically we could do better here if perf. would become an issue
-    const { added, removed, updated } = ElementsDelta.calculate(
-      prevAffectedElements,
-      nextAffectedElements,
+    // calculate complete deltas for affected elements, and squash them back to the current deltas
+    this.squash(
+      // technically we could do better here if perf. would become an issue
+      ElementsDelta.calculate(prevAffectedElements, nextAffectedElements),
     );
 
-    for (const [id, delta] of Object.entries(added)) {
-      this.added[id] = delta;
-    }
-
-    for (const [id, delta] of Object.entries(removed)) {
-      this.removed[id] = delta;
-    }
-
-    for (const [id, delta] of Object.entries(updated)) {
-      this.updated[id] = delta;
-    }
-
     return nextAffectedElements;
   }
 

packages/element/src/store.ts

@@ -76,8 +76,9 @@ type MicroActionsQueue = (() => void)[];
  * Store which captures the observed changes and emits them as `StoreIncrement` events.
  */
 export class Store {
-  // internally used by history
+  // for internal use by history
   public readonly onDurableIncrementEmitter = new Emitter<[DurableIncrement]>();
+  // for public use as part of onIncrement API
   public readonly onStoreIncrementEmitter = new Emitter<
     [DurableIncrement | EphemeralIncrement]
   >();
@@ -239,7 +240,6 @@ export class Store {
     if (!storeDelta.isEmpty()) {
       const increment = new DurableIncrement(storeChange, storeDelta);
 
-      // Notify listeners with the increment
       this.onDurableIncrementEmitter.trigger(increment);
       this.onStoreIncrementEmitter.trigger(increment);
     }