SC-2369: Firebase mirror | Part 3 (#70)

* Fix unsubscribe from events

* Create mirror interfaces

---------

Co-authored-by: Nikita Bereziuk <nikita.bereziuk@sysgears.com>

src/modules/firebase/firebase-mirror/firebase-mirror-core.interface.ts

@@ -0,0 +1,105 @@
+import { skipFirst } from '../../common/common.utils';
+import {
+  SubscriptionService,
+  Unsubscribe,
+} from '../../subscription-manager/subscription-manager.types';
+import {
+  FirebaseSnapshot,
+  FirebaseTable,
+  FirebaseTableReference,
+} from '../firebase.types';
+import { subscribeOnFirebaseEvent } from '../firebase.utils';
+
+export abstract class FirebaseMirrorCoreService<Entity>
+  implements SubscriptionService
+{
+  static dataByTableName: Map<string, Map<string, unknown>> = new Map();
+
+  protected readonly tableName: string;
+
+  constructor(protected readonly reference: FirebaseTableReference<Entity>) {
+    this.tableName = this.getTableName(reference);
+    this.initializeTableData();
+  }
+
+  public async subscribe(): Promise<Unsubscribe> {
+    await this.loadTableData();
+
+    const unsubscribes = [
+      subscribeOnFirebaseEvent<FirebaseTable<Entity>, 'child_changed'>(
+        this.reference,
+        'child_changed',
+        this.entityAddedOrUpdatedHandler,
+      ),
+      subscribeOnFirebaseEvent(
+        this.reference.limitToLast(1),
+        'child_added',
+        skipFirst(this.entityAddedOrUpdatedHandler),
+      ),
+      subscribeOnFirebaseEvent(
+        this.reference,
+        'child_removed',
+        this.entityRemovedHandler,
+      ),
+    ];
+
+    return () => unsubscribes.forEach((unsubscribe) => unsubscribe());
+  }
+
+  protected getTableData(): Map<string, Entity> {
+    const { dataByTableName } = FirebaseMirrorCoreService;
+    const { key: tableName } = this.reference;
+
+    return dataByTableName.get(tableName || '') as Map<string, Entity>;
+  }
+
+  entityAddedOrUpdatedHandler = (snapshot: FirebaseSnapshot<Entity>): void => {
+    const { key } = snapshot;
+    const candidate = snapshot.val();
+
+    if (key && candidate) {
+      this.getTableData().set(key, candidate);
+    }
+  };
+
+  private entityRemovedHandler = (snapshot: FirebaseSnapshot<Entity>): void => {
+    const { key } = snapshot;
+    const candidate = snapshot.val();
+
+    if (key && candidate) {
+      this.getTableData().delete(key);
+    }
+  };
+
+  private getTableName(reference: FirebaseTableReference<Entity>): string {
+    const { key: tableName } = reference;
+
+    if (!tableName) {
+      throw new Error('Table name is not defined');
+    }
+
+    return tableName;
+  }
+
+  private initializeTableData(): void {
+    const { dataByTableName } = FirebaseMirrorCoreService;
+
+    if (!dataByTableName.has(this.tableName)) {
+      dataByTableName.set(this.tableName, new Map());
+    }
+  }
+
+  private async loadTableData(): Promise<void> {
+    const snapshot = await this.reference.get();
+    const tableData = this.getTableData();
+
+    snapshot.forEach((childSnapshot) => {
+      const { key } = childSnapshot;
+      const data = childSnapshot.val();
+
+      if (key && data) {
+        tableData.set(key, data);
+      }
+    });
+  }
+}

src/modules/firebase/firebase-mirror/firebase-mirror.interface.ts

@@ -0,0 +1,13 @@
+import { FirebaseMirrorCoreService } from './firebase-mirror-core.interface';
+
+export abstract class FirebaseMirrorService<
+  Entity,
+> extends FirebaseMirrorCoreService<Entity> {
+  getByKey(key: string): Entity | undefined {
+    return this.getTableData().get(key);
+  }
+
+  getAll(): Array<[string, Entity]> {
+    return Array.from(this.getTableData());
+  }
+}

src/modules/firebase/firebase.utils.ts

@@ -9,5 +9,5 @@ export const subscribeOnFirebaseEvent = <Entity, Event extends EventType>(
 ): (() => void) => {
   ref.on(eventType, eventHandler);
 
-  return () => ref.off(eventType);
+  return () => ref.off(eventType, eventHandler);
 };