import { Auth, User, UserCredential, Unsubscribe } from "firebase/auth";
import { FirebaseApp } from "firebase/app";
export declare class AuthService {
    private readonly auth;
    private googleProvider;
    /**
     * Creates an instance of AuthService.
     * @param {FirebaseApp} app - The initialized Firebase App instance.
     * @throws Error if the FirebaseApp instance is not provided.
     */
    constructor(app: FirebaseApp);
    /**
     * Gets the underlying Firebase Auth instance.
     * @returns {Auth} The Firebase Auth instance.
     */
    getFirebaseAuth(): Auth;
    /**
     * Gets the currently signed-in user.
     * @returns {User | null} The current user object or null if not signed in.
     */
    getCurrentUser(): User | null;
    /**
     * Gets the ID of the currently signed-in user.
     * @returns {string | null} The current user's ID or null if not signed in.
     */
    getCurrentUserId(): string | null;
    /**
     * Signs in a user with email and password.
     * @param {string} email - The user's email.
     * @param {string} password - The user's password.
     * @returns {Promise<UserCredential>} A promise resolving to the user credential.
     */
    signInWithEmailPassword(email: string, password: string): Promise<UserCredential>;
    /**
     * Initiates sign-in with Google using a popup.
     * @returns {Promise<UserCredential>} A promise resolving to the user credential.
     */
    signInWithGoogle(): Promise<UserCredential>;
    /**
     * Signs out the current user.
     * @returns {Promise<void>}
     */
    signOut(): Promise<void>;
    /**
     * Subscribes to changes in the user's authentication state.
     * @param {(user: User | null) => void} callback - Function to call when the auth state changes.
     * @returns {Unsubscribe} A function to unsubscribe from the listener.
     */
    onAuthStateChanged(callback: (user: User | null) => void): Unsubscribe;
}