import { Injectable, inject } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { BehaviorSubject, firstValueFrom, map, Observable, tap } from 'rxjs';

import { getAppConfig } from './app-config.service';
import { AppUser, AuthTokenResponse } from '../interfaces/auth';

const TOKEN_KEY = 'kmtn_access_token';

@Injectable({
  providedIn: 'root',
})
export class AuthService {
  private http = inject(HttpClient);
  private baseUrl = `${getAppConfig().apiBaseUrl}/api/auth`;

  private authStateSubject = new BehaviorSubject<AppUser | null>(null);

  /** Observable that emits the current auth state. */
  readonly authState$: Observable<AppUser | null> = this.authStateSubject.asObservable();

  constructor() {
    // Check for existing token on init
    this._initAuth();
  }

  /** Login with username/password (bootstrap admin). */
  login(username: string, password: string): Observable<AuthTokenResponse> {
    return this.http.post<AuthTokenResponse>(`${this.baseUrl}/login`, {
      username,
      password,
    }).pipe(
      tap((resp) => localStorage.setItem(TOKEN_KEY, resp.access_token)),
    );
  }

  /** Login with Google ID token. */
  loginWithGoogle(idToken: string): Observable<AuthTokenResponse> {
    return this.http.post<AuthTokenResponse>(`${this.baseUrl}/google`, {
      id_token: idToken,
    }).pipe(
      tap((resp) => localStorage.setItem(TOKEN_KEY, resp.access_token)),
    );
  }

  /** Clear stored token and reset auth state. */
  logout(): void {
    localStorage.removeItem(TOKEN_KEY);
    this.authStateSubject.next(null);
  }

  /** Fetch current user info from the API. */
  getCurrentUser(): Promise<AppUser | null> {
    const token = this._getToken();
    if (!token) return Promise.resolve(null);

    return firstValueFrom(
      this.http.get<AppUser>(`${this.baseUrl}/me`).pipe(
        tap((user) => this.authStateSubject.next(user)),
        map((user) => user),
      )
    ).catch(() => {
      this.logout();
      return null;
    });
  }

  /** Check if there is a stored token. */
  isLoggedIn(): boolean {
    return !!this._getToken();
  }

  /** Check if the current user is an admin (synchronous, based on cached state). */
  isAdmin(): boolean {
    return this.authStateSubject.value?.is_admin ?? false;
  }

  /** Get the current user synchronously (from cached state). */
  getUser(): AppUser | null {
    return this.authStateSubject.value;
  }

  // ── Private ──────────────────────────────────────────────

  private _getToken(): string | null {
    return localStorage.getItem(TOKEN_KEY);
  }

  private async _initAuth(): Promise<void> {
    const token = this._getToken();
    if (token) {
      await this.getCurrentUser();
    }
  }
}