Sprint 8: add widget manifest and data source engine

src/app/widgets/registry/widget-manifest.service.ts

@@ -0,0 +1,34 @@
+import { Injectable } from '@angular/core';
+import { HttpClient } from '@angular/common/http';
+import { Observable, catchError, map, of, shareReplay } from 'rxjs';
+import { WidgetManifestEntry, WidgetManifestFile } from '../contracts/widget-manifest.contract';
+
+@Injectable({ providedIn: 'root' })
+export class WidgetManifestService {
+  private readonly manifestUrl = '/assets/mock/bootstrap/widget-manifest.json';
+  private manifest$?: Observable<WidgetManifestFile>;
+
+  constructor(private readonly http: HttpClient) {}
+
+  getManifest(): Observable<WidgetManifestFile> {
+    if (!this.manifest$) {
+      this.manifest$ = this.http.get<WidgetManifestFile>(this.manifestUrl).pipe(
+        shareReplay({ bufferSize: 1, refCount: true }),
+        catchError(() => {
+          this.manifest$ = undefined;
+          return of({ widgets: [] });
+        })
+      );
+    }
+
+    return this.manifest$;
+  }
+
+  getWidgets(): Observable<WidgetManifestEntry[]> {
+    return this.getManifest().pipe(map((manifest) => manifest.widgets ?? []));
+  }
+
+  getWidget(type: string): Observable<WidgetManifestEntry | undefined> {
+    return this.getWidgets().pipe(map((widgets) => widgets.find((widget) => widget.type === type)));
+  }
+}