feat: implement global loading state with interceptor and component

src/app/core/services/global-loading/global-loading.interceptor.spec.ts

@@ -0,0 +1,79 @@
+import '@angular/compiler';
+import { HttpClient, HttpContext, provideHttpClient, withInterceptors } from '@angular/common/http';
+import {
+  HttpTestingController,
+  provideHttpClientTesting
+} from '@angular/common/http/testing';
+import { TestBed } from '@angular/core/testing';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import {
+  SKIP_GLOBAL_LOADING,
+  globalLoadingInterceptor
+} from './global-loading.interceptor';
+import { GlobalLoadingService } from './global-loading.service';
+
+describe('globalLoadingInterceptor', () => {
+  let client: HttpClient;
+  let httpTesting: HttpTestingController;
+  let loadingService: GlobalLoadingService;
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    TestBed.configureTestingModule({
+      providers: [
+        provideHttpClient(withInterceptors([globalLoadingInterceptor])),
+        provideHttpClientTesting()
+      ]
+    });
+
+    client = TestBed.inject(HttpClient);
+    httpTesting = TestBed.inject(HttpTestingController);
+    loadingService = TestBed.inject(GlobalLoadingService);
+  });
+
+  afterEach(() => {
+    httpTesting.verify();
+    TestBed.resetTestingModule();
+    vi.useRealTimers();
+  });
+
+  it('tracks concurrent requests until the last one completes', () => {
+    client.get('/api/first').subscribe();
+    client.get('/api/second').subscribe();
+    vi.advanceTimersByTime(150);
+
+    expect(loadingService.isLoading()).toBe(true);
+
+    httpTesting.expectOne('/api/first').flush({});
+    expect(loadingService.isLoading()).toBe(true);
+
+    httpTesting.expectOne('/api/second').flush({});
+    expect(loadingService.isLoading()).toBe(false);
+  });
+
+  it('stops loading when a request fails', () => {
+    client.get('/api/failing').subscribe({ error: () => undefined });
+    vi.advanceTimersByTime(150);
+
+    expect(loadingService.isLoading()).toBe(true);
+
+    httpTesting.expectOne('/api/failing').flush(
+      { message: 'Error' },
+      { status: 500, statusText: 'Server Error' }
+    );
+
+    expect(loadingService.isLoading()).toBe(false);
+  });
+
+  it('allows background requests to opt out', () => {
+    const context = new HttpContext().set(SKIP_GLOBAL_LOADING, true);
+
+    client.get('/api/background', { context }).subscribe();
+    vi.advanceTimersByTime(150);
+
+    expect(loadingService.isLoading()).toBe(false);
+
+    httpTesting.expectOne('/api/background').flush({});
+  });
+});

src/app/core/services/global-loading/global-loading.interceptor.ts

@@ -0,0 +1,27 @@
+import {
+  HttpContextToken,
+  HttpEvent,
+  HttpHandlerFn,
+  HttpInterceptorFn,
+  HttpRequest
+} from '@angular/common/http';
+import { inject } from '@angular/core';
+import { Observable, finalize } from 'rxjs';
+
+import { GlobalLoadingService } from './global-loading.service';
+
+export const SKIP_GLOBAL_LOADING = new HttpContextToken<boolean>(() => false);
+
+export const globalLoadingInterceptor: HttpInterceptorFn = (
+  request: HttpRequest<unknown>,
+  next: HttpHandlerFn
+): Observable<HttpEvent<unknown>> => {
+  if (request.context.get(SKIP_GLOBAL_LOADING)) {
+    return next(request);
+  }
+
+  const loadingService = inject(GlobalLoadingService);
+  loadingService.start();
+
+  return next(request).pipe(finalize(() => loadingService.stop()));
+};

src/app/core/services/global-loading/global-loading.service.spec.ts

@@ -0,0 +1,65 @@
+import '@angular/compiler';
+import { TestBed } from '@angular/core/testing';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { GlobalLoadingService } from './global-loading.service';
+
+describe('GlobalLoadingService', () => {
+  let service: GlobalLoadingService;
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    TestBed.configureTestingModule({});
+    service = TestBed.inject(GlobalLoadingService);
+  });
+
+  afterEach(() => {
+    TestBed.resetTestingModule();
+    vi.useRealTimers();
+  });
+
+  it('delays the loading state to avoid flashes on fast operations', () => {
+    service.start();
+
+    expect(service.isLoading()).toBe(false);
+
+    service.stop();
+    vi.advanceTimersByTime(150);
+
+    expect(service.isLoading()).toBe(false);
+  });
+
+  it('shows the loading state for an operation that exceeds the delay', () => {
+    service.start();
+    vi.advanceTimersByTime(150);
+
+    expect(service.isLoading()).toBe(true);
+
+    service.stop();
+
+    expect(service.isLoading()).toBe(false);
+  });
+
+  it('stays visible until all concurrent operations finish', () => {
+    service.start();
+    service.start();
+    vi.advanceTimersByTime(150);
+
+    service.stop();
+    expect(service.isLoading()).toBe(true);
+
+    service.stop();
+    expect(service.isLoading()).toBe(false);
+  });
+
+  it('ignores extra stop calls without corrupting the counter', () => {
+    service.stop();
+    service.start();
+    vi.advanceTimersByTime(150);
+
+    expect(service.isLoading()).toBe(true);
+
+    service.stop();
+    expect(service.isLoading()).toBe(false);
+  });
+});

src/app/core/services/global-loading/global-loading.service.ts

@@ -0,0 +1,58 @@
+import { isPlatformBrowser } from '@angular/common';
+import { Injectable, PLATFORM_ID, inject, signal } from '@angular/core';
+
+const SHOW_DELAY_MS = 150;
+
+@Injectable({ providedIn: 'root' })
+export class GlobalLoadingService {
+  private readonly isBrowser = isPlatformBrowser(inject(PLATFORM_ID));
+  private readonly loadingState = signal(false);
+  private pendingOperations = 0;
+  private showTimer: ReturnType<typeof setTimeout> | undefined;
+
+  readonly isLoading = this.loadingState.asReadonly();
+
+  start(): void {
+    if (!this.isBrowser) {
+      return;
+    }
+
+    this.pendingOperations += 1;
+
+    if (this.pendingOperations > 1 || this.loadingState()) {
+      return;
+    }
+
+    this.showTimer = setTimeout(() => {
+      this.showTimer = undefined;
+
+      if (this.pendingOperations > 0) {
+        this.loadingState.set(true);
+      }
+    }, SHOW_DELAY_MS);
+  }
+
+  stop(): void {
+    if (!this.isBrowser || this.pendingOperations === 0) {
+      return;
+    }
+
+    this.pendingOperations -= 1;
+
+    if (this.pendingOperations > 0) {
+      return;
+    }
+
+    this.cancelShowTimer();
+    this.loadingState.set(false);
+  }
+
+  private cancelShowTimer(): void {
+    if (this.showTimer === undefined) {
+      return;
+    }
+
+    clearTimeout(this.showTimer);
+    this.showTimer = undefined;
+  }
+}