fix(firestore): compare #docChanges() to previous listener's snapshot

Actual Firebase behaviour is that adding another #onSnapshot() doesn't change
the outcome of #docChanges() for each of the listeners.
This means that they each compare only to themselves,
and every #get() results in the snapshot comparing to nothing.

Fixes #18

Author: gustavohenke

firestore/document-reference.test.ts

@@ -22,6 +22,11 @@ it("exposes #path", () => {
   expect(doc.path).toBe("/foo/bar");
 });
 
+it("exposes #parent", () => {
+  const doc = firestore.doc("foo/bar");
+  expect(doc.parent.path).toBe("/foo");
+});
+
 it("shares same data as other instances", async () => {
   const doc1 = firestore.doc("foo/bar");
   await doc1.set({ foo: "bar" });
@@ -286,4 +291,16 @@ describe("#delete()", () => {
 
     expect(listener).toHaveBeenCalledTimes(1);
   });
+
+  it("emits change events on the parent collection", async () => {
+    const coll = firestore.collection("foo");
+    const doc = coll.doc("bar");
+    await doc.set({ bla: "blabla" });
+
+    const listener = jest.fn();
+    coll.onSnapshot(listener);
+    await doc.delete();
+
+    expect(listener).toHaveBeenCalledTimes(2);
+  });
 });

firestore/query-snapshot.test.ts

@@ -4,14 +4,15 @@ import { MockFirestore, MockQuerySnapshot } from "./";
 import { MockQueryDocumentSnapshot } from "./document-snapshot";
 import { MockQuery } from "./query";
 
+let snapshot: MockQuerySnapshot | undefined;
 let query: MockQuery;
 beforeEach(() => {
+  snapshot = undefined;
   query = new MockFirestore(createMockInstance(MockApp)).collection("foo");
 });
 
 const createSnapshot = (docs: MockQueryDocumentSnapshot<any>[]) => {
-  const snapshot = new MockQuerySnapshot(query, docs);
-  query.snapshotVersions.push(snapshot);
+  snapshot = new MockQuerySnapshot(query, docs, snapshot);
   return snapshot;
 };
 
@@ -35,7 +36,7 @@ it("exposes #size as the length of #docs", () => {
   expect(query.size).toBe(docs.length);
 });
 
-it("exposes #empty as the true when #docs.length = 0", () => {
+it("exposes #empty as true when #docs.length = 0", () => {
   const docs = [createMockInstance(MockQueryDocumentSnapshot)];
 
   const query1 = createSnapshot(docs);

firestore/query-snapshot.ts

@@ -4,10 +4,6 @@ import { MockQueryDocumentSnapshot } from "./document-snapshot";
 
 export class MockQuerySnapshot<T = firebase.firestore.DocumentData>
   implements firebase.firestore.QuerySnapshot<T> {
-  private get previousSnapshot(): MockQuerySnapshot<T> | undefined {
-    return this.query.snapshotVersions[this.version - 1];
-  }
-
   readonly metadata: firebase.firestore.SnapshotMetadata = {
     fromCache: true,
     hasPendingWrites: false,
@@ -25,7 +21,7 @@ export class MockQuerySnapshot<T = firebase.firestore.DocumentData>
   constructor(
     public readonly query: MockQuery<T>,
     public readonly docs: MockQueryDocumentSnapshot<T>[],
-    private readonly version: number = query.snapshotVersions.length
+    private readonly previousSnapshot?: MockQuerySnapshot<T> | undefined
   ) {}
 
   docChanges(

firestore/query.ts

@@ -24,7 +24,6 @@ export class MockQuery<T = firebase.firestore.DocumentData> implements firebase.
   protected filters: Record<string, QueryFilter> = {};
   protected ordering?: Ordering;
   private noInitialSnapshot = false;
-  public snapshotVersions: MockQuerySnapshot<T>[] = [];
 
   protected get emitter() {
     const emitter = this.firestore.collectionEvents.get(this.path) || new EventEmitter();
@@ -45,7 +44,6 @@ export class MockQuery<T = firebase.firestore.DocumentData> implements firebase.
 
     // TODO: this emits even if there wasn't an actual change with the current filters
     const snapshot = await this.get();
-    this.snapshotVersions.push(snapshot);
     this.emitter.emit(QUERY_SNAPSHOT_NEXT_EVENT, [snapshot]);
   }
 
@@ -58,8 +56,6 @@ export class MockQuery<T = firebase.firestore.DocumentData> implements firebase.
     const query = new MockQuery(this.firestore, this.path, this.converter);
     Object.assign(query, this);
     query.filters = Object.assign({}, this.filters);
-    // Extending the original query with new filters/ordering voids the snapshot version cache.
-    query.snapshotVersions = [];
     return query;
   }
 
@@ -299,7 +295,7 @@ export class MockQuery<T = firebase.firestore.DocumentData> implements firebase.
     onCompletion?: (() => void) | undefined
   ): () => void;
   onSnapshot(options: any, onNext?: any, onError?: any, onCompletion?: any): () => void {
-    let actualListeners: Observer<firebase.firestore.QuerySnapshot<T>>;
+    let actualListeners: Observer<MockQuerySnapshot<T>>;
 
     if (typeof options === "object") {
       if (typeof onNext === "object") {
@@ -319,31 +315,29 @@ export class MockQuery<T = firebase.firestore.DocumentData> implements firebase.
       };
     }
 
+    let prevSnapshot: MockQuerySnapshot<T>;
     const { next, error } = actualListeners;
-    this.emitter.on(QUERY_SNAPSHOT_NEXT_EVENT, next);
+    const actualNext = (snapshot: MockQuerySnapshot<T>) => {
+      const surrogate = new MockQuerySnapshot(this, snapshot.docs, prevSnapshot);
+      next(surrogate);
+      prevSnapshot = surrogate;
+    };
+    this.emitter.on(QUERY_SNAPSHOT_NEXT_EVENT, actualNext);
     error && this.emitter.on(QUERY_SNAPSHOT_ERROR_EVENT, error);
 
     if (!this.noInitialSnapshot) {
-      this.get().then((snapshot) => next(snapshot));
+      this.get().then((snapshot) => actualNext(snapshot));
     }
 
     return () => {
-      this.emitter.off(QUERY_SNAPSHOT_NEXT_EVENT, next);
+      this.emitter.off(QUERY_SNAPSHOT_NEXT_EVENT, actualNext);
       error && this.emitter.off(QUERY_SNAPSHOT_ERROR_EVENT, error);
     };
   }
 
   withConverter<U>(converter: firebase.firestore.FirestoreDataConverter<U>): MockQuery<U> {
     const query = (this.clone() as unknown) as MockQuery<U>;
     query.converter = converter;
-    query.snapshotVersions = this.snapshotVersions.map(
-      (snapshot, version) =>
-        new MockQuerySnapshot(
-          query,
-          (snapshot.docs as unknown) as MockQueryDocumentSnapshot<U>[],
-          version
-        )
-    );
     return query;
   }
 }