import { Injectable } from '@angular/core';
import { NavigationEnd, Router } from '@angular/router';
import { filter } from 'rxjs/operators';

@Injectable({
  providedIn: 'root',
})
export class NavigationService {
  private readonly CURRENT_URL_KEY = 'currentUrl';
  private readonly PREVIOUS_URL_KEY = 'previousUrl';

  currentUrl: string | null;
  previousUrl: string | null;

  constructor(private router: Router) {
    this.currentUrl = sessionStorage.getItem(this.CURRENT_URL_KEY);
    this.previousUrl = sessionStorage.getItem(this.PREVIOUS_URL_KEY);

    this.router.events
      .pipe(filter((event): event is NavigationEnd => event instanceof NavigationEnd))
      .subscribe((event) => {
        const newUrl = event.urlAfterRedirects;

        // Ignore duplicate events
        if (newUrl === this.currentUrl) {
          return;
        }

        this.previousUrl = this.currentUrl;
        this.currentUrl = newUrl;

        if (this.previousUrl) {
          sessionStorage.setItem(this.PREVIOUS_URL_KEY, this.previousUrl);
        }

        sessionStorage.setItem(this.CURRENT_URL_KEY, this.currentUrl);
      });
  }

  canGoBack(): boolean {
    return !!this.previousUrl;
  }

  back(fallbackUrl = '/'): void {
    if (this.canGoBack()) {
      window.history.back();
    } else {
      this.router.navigateByUrl(fallbackUrl);
    }
  }
}