Asset tracking.

Asset caching.
refs #37

frontend/src/app/services/assets.service.ts

@@ -1,7 +1,8 @@
 import { Injectable } from '@angular/core';
 import { HttpClient } from '@angular/common/http';
-import { ReplaySubject } from 'rxjs';
+import { ReplaySubject, Observable } from 'rxjs';
 import { environment } from 'src/environments/environment';
+import { shareReplay } from 'rxjs/operators';
 
 @Injectable({
   providedIn: 'root'
@@ -9,24 +10,13 @@ import { environment } from 'src/environments/environment';
 export class AssetsService {
   network = environment.network;
 
-  assetsMinimal$ = new ReplaySubject<any>(1);
+  getAssetsJson$: Observable<any>;
+  getAssetsMinimalJson$: Observable<any>;
 
   constructor(
     private httpClient: HttpClient,
   ) {
-    if (this.network === 'liquid') {
-      this.getAssetsMinimalJson$();
-    }
-  }
-
-  getAssetsMinimalJson$() {
-    this.httpClient.get('/resources/assets.minimal.json')
-    .subscribe((data) => {
-      this.assetsMinimal$.next(data);
-    });
-  }
-
-  getAssetsJson$() {
-    return this.httpClient.get('/resources/assets.json');
+    this.getAssetsJson$ = this.httpClient.get('/resources/assets.json').pipe(shareReplay());
+    this.getAssetsMinimalJson$ = this.httpClient.get('/resources/assets.minimal.json').pipe(shareReplay());
   }
 }