Shared services

projects/common/src/fm/services/cache-service.ts

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+import { Injectable } from '@angular/core';
+import { IItem, ItemService } from '@farmmaps/common';
+import { OAuthService } from 'angular-oauth2-oidc';
+import { Observable, ReplaySubject, Subscription, timer } from 'rxjs';
+import { catchError, take } from 'rxjs/operators';
+
+const REFRESH_INTERVAL = 15 * 60 * 1000;  // 15m
+
+@Injectable({ providedIn: 'root'})
+export class CacheService {
+  private proxyCacheMap: { [key: string]: ReplaySubject<IItem[]> } = {};
+  private subscriptionMap: { [key: string]: Subscription } = {};
+
+  constructor(private itemService: ItemService, public oauthService: OAuthService) {
+    timer(0, REFRESH_INTERVAL).subscribe(() => {
+      this.subscriptionMap = {};
+    })
+  }
+
+  getItemList(itemType: string) : Observable<IItem[]> {
+    if (!this.proxyCacheMap[itemType]) {
+      this.proxyCacheMap[itemType] = new ReplaySubject(1);
+    }
+
+    if (this.oauthService.getAccessToken() != null && !this.subscriptionMap[itemType]) {
+      this.subscriptionMap[itemType] = this.itemService.getItemList(itemType)
+        .pipe(          
+          catchError(error => {
+            this.subscriptionMap[itemType].unsubscribe();
+            this.subscriptionMap[itemType] = null;
+            throw error;
+          }),
+
+      ).subscribe(items => {
+        this.proxyCacheMap[itemType].next(items);
+      });
+    }
+
+    return this.proxyCacheMap[itemType].asObservable()
+      .pipe(
+        take(1)
+      );
+  }
+}