changes

src/app/services/api.service.ts

@@ -1,7 +1,7 @@
 import { Injectable } from '@angular/core';
 import { HttpClient, HttpParams } from '@angular/common/http';
-import { Observable } from 'rxjs';
-import { map } from 'rxjs/operators';
+import { Observable, timer } from 'rxjs';
+import { map, retry } from 'rxjs/operators';
 import { Category, Item } from '../models';
 import { environment } from '../../environments/environment';
 
@@ -11,6 +11,11 @@ import { environment } from '../../environments/environment';
 export class ApiService {
   private readonly baseUrl = environment.apiUrl;
 
+  private readonly retryConfig = {
+    count: 2,
+    delay: (error: unknown, retryCount: number) => timer(Math.pow(2, retryCount) * 500)
+  };
+
   constructor(private http: HttpClient) {}
 
   private normalizeItem(item: Item): Item {
@@ -32,7 +37,7 @@ export class ApiService {
   }
 
   getCategories(): Observable<Category[]> {
-    return this.http.get<Category[]>(`${this.baseUrl}/category`);
+    return this.http.get<Category[]>(`${this.baseUrl}/category`).pipe(retry(this.retryConfig));
   }
 
   getCategoryItems(categoryID: number, count: number = 50, skip: number = 0): Observable<Item[]> {
@@ -40,12 +45,12 @@ export class ApiService {
       .set('count', count.toString())
       .set('skip', skip.toString());
     return this.http.get<Item[]>(`${this.baseUrl}/category/${categoryID}`, { params })
-      .pipe(map(items => this.normalizeItems(items)));
+      .pipe(retry(this.retryConfig), map(items => this.normalizeItems(items)));
   }
 
   getItem(itemID: number): Observable<Item> {
     return this.http.get<Item>(`${this.baseUrl}/item/${itemID}`)
-      .pipe(map(item => this.normalizeItem(item)));
+      .pipe(retry(this.retryConfig), map(item => this.normalizeItem(item)));
   }
 
   searchItems(search: string, count: number = 50, skip: number = 0): Observable<{ items: Item[], total: number }> {
@@ -55,6 +60,7 @@ export class ApiService {
       .set('skip', skip.toString());
     return this.http.get<{ items: Item[], total: number, count: number, skip: number }>(`${this.baseUrl}/searchitems`, { params })
       .pipe(
+        retry(this.retryConfig),
         map(response => ({
           items: this.normalizeItems(response?.items || []),
           total: response?.total || 0
@@ -162,6 +168,6 @@ export class ApiService {
       params = params.set('category', categoryID.toString());
     }
     return this.http.get<Item[]>(`${this.baseUrl}/randomitems`, { params })
-      .pipe(map(items => this.normalizeItems(items)));
+      .pipe(retry(this.retryConfig), map(items => this.normalizeItems(items)));
   }
 }

src/app/services/prefetch.service.ts

@@ -0,0 +1,15 @@
+import { Injectable } from '@angular/core';
+import { ApiService } from './api.service';
+
+@Injectable({ providedIn: 'root' })
+export class PrefetchService {
+  private prefetched = new Set<number>();
+
+  constructor(private api: ApiService) {}
+
+  prefetchItem(itemID: number): void {
+    if (this.prefetched.has(itemID)) return;
+    this.prefetched.add(itemID);
+    this.api.getItem(itemID).subscribe();
+  }
+}