feat(signposting): add signposting service

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

@@ -0,0 +1,73 @@
+import { DOCUMENT } from '@angular/common';
+import { RESPONSE_INIT } from '@angular/core';
+import { TestBed } from '@angular/core/testing';
+
+import { SignpostingService } from './signposting.service';
+
+describe('Service: Signposting', () => {
+  let service: SignpostingService;
+  let mockDocument: Document;
+  let mockResponseInit: ResponseInit;
+
+  beforeEach(() => {
+    mockResponseInit = {
+      headers: new Headers(),
+    };
+    mockDocument = {
+      createElement: jest.fn((tagName: string) => {
+        const element: any = {
+          tagName,
+          attributes: {} as Record<string, string>,
+          setAttribute: function (attrName: string, attrValue: string) {
+            this.attributes[attrName] = attrValue;
+          },
+          getAttribute: function (attrName: string) {
+            return this.attributes[attrName];
+          },
+        };
+        return element;
+      }),
+      head: {
+        appendChild: jest.fn(),
+      },
+    } as any;
+    TestBed.configureTestingModule({
+      providers: [
+        SignpostingService,
+        { provide: DOCUMENT, useValue: mockDocument },
+        { provide: RESPONSE_INIT, useValue: mockResponseInit },
+      ],
+    });
+
+    service = TestBed.inject(SignpostingService);
+    mockDocument = TestBed.inject(DOCUMENT);
+    mockResponseInit = TestBed.inject(RESPONSE_INIT) as ResponseInit;
+  });
+
+  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(mockDocument.createElement).toHaveBeenNthCalledWith(1, 'link');
+    expect(mockDocument.createElement).toHaveBeenNthCalledWith(2, 'link');
+
+    expect(mockDocument.head.appendChild).toHaveBeenCalledTimes(2);
+
+    const firstLinkElement = (mockDocument.head.appendChild as jest.Mock).mock.calls[0][0];
+    expect(firstLinkElement.getAttribute('rel')).toBe('linkset');
+    expect(firstLinkElement.getAttribute('href')).toBe('https://staging3.osf.io/metadata/abcde/?format=linkset');
+    expect(firstLinkElement.getAttribute('type')).toBe('application/linkset');
+    const secondLinkElement = (mockDocument.head.appendChild as jest.Mock).mock.calls[1][0];
+    expect(secondLinkElement.getAttribute('rel')).toBe('linkset');
+    expect(secondLinkElement.getAttribute('href')).toBe(
+      'https://staging3.osf.io/metadata/abcde/?format=linkset%2Bjson'
+    );
+    expect(secondLinkElement.getAttribute('type')).toBe('application/linkset+json');
+  });
+});

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

@@ -0,0 +1,98 @@
+import { of } from 'rxjs';
+
+import { DOCUMENT } from '@angular/common';
+import { inject, Injectable, RESPONSE_INIT } from '@angular/core';
+
+import { ENVIRONMENT } from '@core/provider/environment.provider';
+
+export interface SignpostingLink {
+  rel: string;
+  href: string;
+  type: string;
+}
+
+export const linksetType = 'application/linkset';
+export const linksetJsonType = 'application/linkset+json';
+
+@Injectable({
+  providedIn: 'root',
+})
+export class SignpostingService {
+  private readonly document = inject(DOCUMENT);
+  private readonly environment = inject(ENVIRONMENT);
+  private readonly responseInit = inject(RESPONSE_INIT, { optional: true });
+
+  addSignposting(guid: string): void {
+    const baseUrl = `${this.environment.webUrl}/metadata/${guid}/`;
+    const linksetUrl = new URL(baseUrl);
+    linksetUrl.searchParams.set('format', 'linkset');
+    const linksetJsonUrl = new URL(baseUrl);
+    linksetJsonUrl.searchParams.set('format', 'linkset+json');
+    const signpostingLinks: SignpostingLink[] = [
+      {
+        rel: 'linkset',
+        href: linksetUrl.toString(),
+        type: linksetType,
+      },
+      {
+        rel: 'linkset',
+        href: linksetJsonUrl.toString(),
+        type: linksetJsonType,
+      },
+    ];
+
+    this.addSignpostingLinkHeaders(signpostingLinks);
+    this.addSignpostingLinkTags(signpostingLinks);
+  }
+
+  private addSignpostingLinkHeaders(links: SignpostingLink[]): void {
+    of(links).subscribe({
+      next: (links) => {
+        if (!this.responseInit || !this.responseInit.headers) {
+          return;
+        }
+
+        const headers =
+          this.responseInit?.headers instanceof Headers
+            ? this.responseInit.headers
+            : new Headers(this.responseInit?.headers);
+
+        const linkHeader = this.formatLinkHeaders(links);
+        headers.set('Link', linkHeader);
+
+        this.responseInit.headers = headers;
+      },
+    });
+  }
+
+  private addSignpostingLinkTags(links: SignpostingLink[]): void {
+    of(links).subscribe({
+      next: (links) => {
+        const linkElements = this.formatLinkElements(links);
+        linkElements.forEach((linkElement) => {
+          this.document.head.appendChild(linkElement);
+        });
+      },
+    });
+  }
+
+  private formatLinkHeaders(links: SignpostingLink[]): string {
+    return links
+      .map((link) => {
+        const parts = [`<${link.href}>`, `rel="${link.rel}"`];
+        if (link.type) parts.push(`type="${link.type}"`);
+        return parts.join('; ');
+      })
+      .join(', ');
+  }
+
+  private formatLinkElements(links: SignpostingLink[]): HTMLLinkElement[] {
+    return links.map((link) => {
+      const linkElement = this.document.createElement('link');
+      linkElement.setAttribute('rel', link.rel);
+      linkElement.setAttribute('href', link.href);
+      linkElement.setAttribute('type', link.type);
+      return linkElement;
+    });
+  }
+}