import { computed, inject, Injectable, Signal, signal, WritableSignal } from "@angular/core";
import { RegisterUserRequest, User } from "../../../core/models/user.model";
import { HttpClient, HttpErrorResponse } from "@angular/common/http";
import { API_URL, BACKEND_URL } from "../../../core/tokens/api-url-tokens";
import { switchMap, tap } from "rxjs";
import { LocalStorageService } from "../../../core/services/local-storage.service";

export enum AuthState {
  Loading = "loading",
  Authenticated = "authenticated",
  Unauthenticated = "unauthenticated",
}

/**
 * UserService - manages user related operations
 *
 * ## Auth States
 * - loading: user is being fetched from the server
 * - authenticated: user is authenticated
 * - unauthenticated: user is not authenticated
 */

@Injectable({
  providedIn: "root",
})
export class AuthService {
  // User states
  readonly authState: WritableSignal<AuthState>;
  readonly user: WritableSignal<User | null>;

  // Computed state for easy checking
  readonly isAuthenticated: Signal<boolean>;
  // Dependent services
  private localStorage = inject(LocalStorageService);
  private http: HttpClient = inject(HttpClient);
  // Constants
  private readonly userKey = "ekart_user";
  private apiUrl = inject(API_URL);
  private backendURL = inject(BACKEND_URL);

  constructor() {
    const cachedUser = this.localStorage.getItem<User>(this.userKey);
    this.authState = signal<AuthState>(
      cachedUser ? AuthState.Authenticated : AuthState.Unauthenticated,
    );
    this.user = signal<User | null>(cachedUser);
    this.isAuthenticated = computed(() => !!this.user());
  }

  register(userRequest: RegisterUserRequest) {
    return this.http.post(`${this.apiUrl}/register`, userRequest);
  }

  /**
   * Laravel API expects the csrf cookie to be set before making a request.
   * First set the cookie then attempt to login.
   * If the login is successful, set the user in the state.
   */
  login(credentials: { email: string; password: string }) {
    return this.getCsrfCookie().pipe(
      switchMap(() =>
        this.http.post(`${this.backendURL}/login`, credentials, { observe: "response" }),
      ),
      switchMap(() => this.getCurrentUser()),
    );
  }

  getCurrentUser() {
    return this.http.get<User>(`${this.apiUrl}/user`).pipe(
      tap({
        next: (user) => this.setAuth(user),
        error: (error: HttpErrorResponse) => this.purgeAuth(),
      }),
    );
  }

  logout() {
    return this.http.post(`${this.backendURL}/logout`, {}).pipe(
      tap({
        next: () => this.purgeAuth(),
      }),
    );
  }

  private getCsrfCookie() {
    return this.http.get(`${this.backendURL}/sanctum/csrf-cookie`);
  }

  private setAuth(user: User) {
    this.localStorage.setItem<User>(this.userKey, user);
    this.user.set(user);
    this.authState.set(AuthState.Authenticated);
  }

  private purgeAuth() {
    this.localStorage.removeItem(this.userKey);
    this.user.set(null);
    this.authState.set(AuthState.Unauthenticated);
  }
}