import { User } from "../entities/User";
export declare class DatabaseService {
    private static instance;
    private dataSource;
    private userRepository;
    private constructor();
    static getInstance(): DatabaseService;
    initialize(): Promise<void>;
    findUserByEmail(email: string): Promise<User | null>;
    createUser(userData: Partial<User>): Promise<User>;
    /**
     * Update a user by id with new user data
     * @param id - User ID (either number or string, depending on DB type)
     * @param userData - The data to update in the user record
     * @returns The updated user, or null if no user was found
     */
    updateUser(id: string | number, userData: Partial<User>): Promise<User | null>;
}