import { Injectable, computed, inject, signal } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Router } from '@angular/router';
import { Observable, tap } from 'rxjs';

interface TokenResponse { token: string; email: string; }

/** JWT in localStorage; who is logged in. */
@Injectable({ providedIn: 'root' })
export class AuthService {
  private http = inject(HttpClient);
  private router = inject(Router);

  readonly email = signal<string | null>(read('email'));
  /** Administrator who opened this mailbox (Settings → MAILBOXES → Open), or null */
  readonly openedBy = signal<string | null>(read('adminEmail'));
  readonly loggedIn = computed(() => this.email() !== null && read('token') !== null);

  login(email: string, password: string): Observable<TokenResponse> {
    return this.http.post<TokenResponse>('/api/login', { email, password }).pipe(tap(r => this.store(r)));
  }

  register(email: string, password: string, displayName: string): Observable<TokenResponse> {
    return this.http.post<TokenResponse>('/api/register', { email, password, displayName }).pipe(tap(r => this.store(r)));
  }

  token(): string | null { return read('token'); }

  /** Administrator opens another mailbox: its session, the admin session kept to come back. */
  openAs(response: TokenResponse): void {
    const adminToken = read('token');
    const adminEmail = read('email');
    try {
      if (adminToken && adminEmail && !read('adminToken')) {
        localStorage.setItem('adminToken', adminToken);
        localStorage.setItem('adminEmail', adminEmail);
      }
    } catch { /* storage blocked */ }
    this.store(response);
    this.openedBy.set(read('adminEmail'));
  }

  /**
   * Switch to another mailbox of the same login (left menu). Going back to the mailbox an administrator came
   * from ends the administrator's visit.
   */
  switchTo(response: TokenResponse): void {
    if (this.openedBy() && response.email === this.openedBy()) {
      this.backToAdmin();
      return;
    }
    this.store(response);
  }

  /** Back to the administrator's own mailbox. */
  backToAdmin(): void {
    const token = read('adminToken');
    const email = read('adminEmail');
    try {
      localStorage.removeItem('adminToken');
      localStorage.removeItem('adminEmail');
    } catch { /* storage blocked */ }
    this.openedBy.set(null);
    if (token && email) { this.store({ token, email }); } else { this.clear(); }
  }

  logout(): void {
    this.clear();
    this.router.navigate(['/login']);
  }

  clear(): void {
    try {
      localStorage.removeItem('token');
      localStorage.removeItem('email');
      localStorage.removeItem('adminToken');
      localStorage.removeItem('adminEmail');
    } catch { /* storage blocked */ }
    this.email.set(null);
    this.openedBy.set(null);
  }

  private store(response: TokenResponse): void {
    try {
      localStorage.setItem('token', response.token);
      localStorage.setItem('email', response.email);
    } catch { /* storage blocked: logged in for this tab only */ }
    this.email.set(response.email);
  }
}

function read(key: string): string | null {
  try { return localStorage.getItem(key); } catch { return null; }
}