feat(signposting): add signposting service

src/app/shared/models/signposting.model.ts

@@ -0,0 +1,8 @@
+export const LINKSET_TYPE = 'application/linkset';
+export const LINKSET_JSON_TYPE = 'application/linkset+json';
+
+export interface SignpostingLink {
+  rel: string;
+  href: string;
+  type: string;
+}

src/app/shared/services/signposting.service.spec.ts

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+import { RendererFactory2, RESPONSE_INIT } from '@angular/core';
+import { TestBed } from '@angular/core/testing';
+
+import { SignpostingService } from './signposting.service';
+
+describe('Service: Signposting', () => {
+  let service: SignpostingService;
+  let mockResponseInit: ResponseInit;
+  let createdLinks: Record<string, string>[];
+  let mockAppendChild: jest.Mock;
+
+  beforeEach(() => {
+    createdLinks = [];
+    mockAppendChild = jest.fn();
+    mockResponseInit = { headers: new Headers() };
+
+    TestBed.configureTestingModule({
+      providers: [
+        SignpostingService,
+        { provide: RESPONSE_INIT, useValue: mockResponseInit },
+        {
+          provide: RendererFactory2,
+          useValue: {
+            createRenderer: () => ({
+              createElement: jest.fn().mockImplementation(() => {
+                const link: Record<string, string> = {};
+                createdLinks.push(link);
+                return link;
+              }),
+              setAttribute: jest.fn().mockImplementation((el, attr, value) => {
+                el[attr] = value;
+              }),
+              appendChild: mockAppendChild,
+            }),
+          },
+        },
+      ],
+    });
+
+    service = TestBed.inject(SignpostingService);
+  });
+
+  it('should set headers using addSignposting', () => {
+    service.addSignposting('abcde');
+    const linkHeader = (mockResponseInit.headers as Headers).get('Link');
+    expect(linkHeader).toBe(
+      '<https://staging3.osf.io/metadata/abcde/?format=linkset>; rel="linkset"; type="application/linkset", <https://staging3.osf.io/metadata/abcde/?format=linkset%2Bjson>; rel="linkset"; type="application/linkset+json"'
+    );
+  });
+
+  it('should add link tags using addSignposting', () => {
+    service.addSignposting('abcde');
+
+    expect(createdLinks).toEqual([
+      {
+        rel: 'linkset',
+        href: 'https://staging3.osf.io/metadata/abcde/?format=linkset',
+        type: 'application/linkset',
+      },
+      {
+        rel: 'linkset',
+        href: 'https://staging3.osf.io/metadata/abcde/?format=linkset%2Bjson',
+        type: 'application/linkset+json',
+      },
+    ]);
+    expect(mockAppendChild).toHaveBeenCalledTimes(2);
+  });
+});

src/app/shared/services/signposting.service.ts

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+import { DOCUMENT } from '@angular/common';
+import { inject, Injectable, RendererFactory2, RESPONSE_INIT } from '@angular/core';
+
+import { ENVIRONMENT } from '@core/provider/environment.provider';
+
+import { LINKSET_JSON_TYPE, LINKSET_TYPE, SignpostingLink } from '../models/signposting.model';
+
+@Injectable({
+  providedIn: 'root',
+})
+export class SignpostingService {
+  private readonly document = inject(DOCUMENT);
+  private readonly environment = inject(ENVIRONMENT);
+  private readonly responseInit = inject(RESPONSE_INIT, { optional: true });
+  private readonly renderer = inject(RendererFactory2).createRenderer(null, null);
+
+  addSignposting(guid: string): void {
+    const links = this.generateSignpostingLinks(guid);
+
+    this.addSignpostingLinkHeaders(links);
+    this.addSignpostingLinkTags(links);
+  }
+
+  private generateSignpostingLinks(guid: string): SignpostingLink[] {
+    const baseUrl = `${this.environment.webUrl}/metadata/${guid}/`;
+
+    return [
+      {
+        rel: 'linkset',
+        href: this.buildUrl(baseUrl, 'linkset'),
+        type: LINKSET_TYPE,
+      },
+      {
+        rel: 'linkset',
+        href: this.buildUrl(baseUrl, 'linkset+json'),
+        type: LINKSET_JSON_TYPE,
+      },
+    ];
+  }
+
+  private buildUrl(base: string, format: string): string {
+    const url = new URL(base);
+    url.searchParams.set('format', format);
+    return url.toString();
+  }
+
+  private addSignpostingLinkHeaders(links: SignpostingLink[]): void {
+    if (!this.responseInit) return;
+
+    const headers =
+      this.responseInit.headers instanceof Headers ? this.responseInit.headers : new Headers(this.responseInit.headers);
+
+    const linkHeaderValue = links.map((link) => `<${link.href}>; rel="${link.rel}"; type="${link.type}"`).join(', ');
+
+    headers.set('Link', linkHeaderValue);
+    this.responseInit.headers = headers;
+  }
+
+  private addSignpostingLinkTags(links: SignpostingLink[]): void {
+    links.forEach((link) => {
+      const linkElement = this.renderer.createElement('link');
+      this.renderer.setAttribute(linkElement, 'rel', link.rel);
+      this.renderer.setAttribute(linkElement, 'href', link.href);
+      this.renderer.setAttribute(linkElement, 'type', link.type);
+      this.renderer.appendChild(this.document.head, linkElement);
+    });
+  }
+}