[firestore][android][js] Add document onSnapshot support plus tests

lib/modules/firestore/DocumentReference.js

@@ -19,6 +19,9 @@ export type WriteResult = {
   writeTime: string,
 }
 
+// track all event registrations
+let listeners = 0;
+
  /**
  * @class DocumentReference
  */
@@ -89,8 +92,30 @@ export default class DocumentReference {
     throw new Error(INTERNALS.STRINGS.ERROR_UNSUPPORTED_CLASS_METHOD('DocumentReference', 'getCollections'));
   }
 
-  onSnapshot(onNext: () => any, onError?: () => any): () => void {
-    // TODO
+  onSnapshot(onNext: Function, onError?: Function): () => void {
+    // TODO: Validation
+    const listenerId = listeners++;
+
+    // Listen to snapshot events
+    this._firestore.on(
+      this._firestore._getAppEventName(`onDocumentSnapshot:${listenerId}`),
+      onNext,
+    );
+
+    // Listen for snapshot error events
+    if (onError) {
+      this._firestore.on(
+        this._firestore._getAppEventName(`onDocumentSnapshotError:${listenerId}`),
+        onError,
+      );
+    }
+
+    // Add the native listener
+    this._firestore._native
+      .documentOnSnapshot(this.path, listenerId);
+
+    // Return an unsubscribe method
+    return this._offDocumentSnapshot.bind(this, listenerId, onNext);
   }
 
   set(data: { [string]: any }, writeOptions?: WriteOptions): Promise<WriteResult> {
@@ -105,16 +130,11 @@ export default class DocumentReference {
   }
 
   /**
-   * INTERNALS
+   * Remove auth change listener
+   * @param listener
    */
-
-  /**
-  * Generate a string that uniquely identifies this DocumentReference
-  *
-  * @return {string}
-  * @private
-  */
-  _getDocumentKey() {
-    return `$${this._firestore._appName}$/${this.path}`;
+  _offDocumentSnapshot(listenerId: number, listener: Function) {
+    this._firestore.log.info('Removing onDocumentSnapshot listener');
+    this._firestore.removeListener(this._firestore._getAppEventName(`onDocumentSnapshot:${listenerId}`), listener);
   }
 }

lib/modules/firestore/Query.js

@@ -200,7 +200,7 @@ export default class Query {
   }
 
   stream(): Stream<DocumentSnapshot> {
-
+    throw new Error(INTERNALS.STRINGS.ERROR_UNSUPPORTED_CLASS_METHOD('Query', 'stream'));
   }
 
   where(fieldPath: string, opStr: Operator, value: any): Query {

lib/modules/firestore/index.js

@@ -16,6 +16,14 @@ import INTERNALS from './../../internals';
 const unquotedIdentifier_ = '(?:[A-Za-z_][A-Za-z_0-9]*)';
 const UNQUOTED_IDENTIFIER_REGEX = new RegExp(`^${unquotedIdentifier_}$`);
 
+type DocumentSyncEvent = {
+  appName: string,
+  document?: DocumentSnapshot,
+  error?: Object,
+  listenerId: number,
+  path: string,
+}
+
 /**
  * @class Firestore
  */
@@ -28,6 +36,20 @@ export default class Firestore extends ModuleBase {
   constructor(firebaseApp: Object, options: Object = {}) {
     super(firebaseApp, options, true);
     this._referencePath = new Path([]);
+
+    this.addListener(
+      // sub to internal native event - this fans out to
+      // public event name: onCollectionSnapshot
+      this._getAppEventName('firestore_collection_sync_event'),
+      this._onCollectionSyncEvent.bind(this),
+    );
+
+    this.addListener(
+      // sub to internal native event - this fans out to
+      // public event name: onDocumentSnapshot
+      this._getAppEventName('firestore_document_sync_event'),
+      this._onDocumentSyncEvent.bind(this),
+    );
   }
 
   batch(): WriteBatch {
@@ -107,6 +129,37 @@ export default class Firestore extends ModuleBase {
 
     return fieldPath;
   }
+
+  /**
+   * INTERNALS
+   */
+
+  /**
+   * Internal collection sync listener
+   * @param event
+   * @private
+   */
+  _onCollectionSyncEvent(event: DocumentSyncEvent) {
+    if (event.error) {
+      this.emit(this._getAppEventName(`onCollectionSnapshotError:${event.listenerId}`, event.error));
+    } else {
+      this.emit(this._getAppEventName(`onCollectionSnapshot:${event.listenerId}`, event.document));
+    }
+  }
+
+  /**
+   * Internal document sync listener
+   * @param event
+   * @private
+   */
+  _onDocumentSyncEvent(event: DocumentSyncEvent) {
+    if (event.error) {
+      this.emit(this._getAppEventName(`onDocumentSnapshotError:${event.listenerId}`), event.error);
+    } else {
+      const snapshot = new DocumentSnapshot(this, event.document);
+      this.emit(this._getAppEventName(`onDocumentSnapshot:${event.listenerId}`), snapshot);
+    }
+  }
 }
 
 export const statics = {

lib/utils/ModuleBase.js

@@ -29,6 +29,10 @@ const NATIVE_MODULE_EVENTS = {
     'database_transaction_event',
     // 'database_server_offset', // TODO
   ],
+  Firestore: [
+    'firestore_collection_sync_event',
+    'firestore_document_sync_event',
+  ],
 };
 
 const DEFAULTS = {