initial commit

src/app/@core/utils/seo.service.ts

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+import { Injectable, Inject, PLATFORM_ID, OnDestroy } from '@angular/core';
+import { isPlatformBrowser } from '@angular/common';
+import { NavigationEnd, Router } from '@angular/router';
+import { NB_DOCUMENT } from '@nebular/theme';
+import { filter, takeUntil } from 'rxjs/operators';
+import { Subject } from 'rxjs';
+
+@Injectable()
+export class SeoService implements OnDestroy {
+
+  private readonly destroy$ = new Subject<void>();
+  private readonly dom: Document;
+  private readonly isBrowser: boolean;
+  private linkCanonical: HTMLLinkElement;
+
+  constructor(
+    private router: Router,
+    @Inject(NB_DOCUMENT) document,
+    @Inject(PLATFORM_ID) platformId,
+  ) {
+    this.isBrowser = isPlatformBrowser(platformId);
+    this.dom = document;
+
+    if (this.isBrowser) {
+      this.createCanonicalTag();
+    }
+  }
+
+  ngOnDestroy() {
+    this.destroy$.next();
+    this.destroy$.complete();
+  }
+
+  createCanonicalTag() {
+    this.linkCanonical = this.dom.createElement('link');
+    this.linkCanonical.setAttribute('rel', 'canonical');
+    this.dom.head.appendChild(this.linkCanonical);
+    this.linkCanonical.setAttribute('href', this.getCanonicalUrl());
+  }
+
+  trackCanonicalChanges() {
+    if (!this.isBrowser) {
+      return;
+    }
+
+    this.router.events.pipe(
+      filter((event) => event instanceof NavigationEnd),
+      takeUntil(this.destroy$),
+    )
+      .subscribe(() => {
+        this.linkCanonical.setAttribute('href', this.getCanonicalUrl());
+      });
+  }
+
+  private getCanonicalUrl(): string {
+    return this.dom.location.origin + this.dom.location.pathname;
+  }
+}