package ins.frontend.utils;

import org.openautonomousconnection.webserver.utils.PasswordHasher;

import java.util.Objects;

/**
 * Registration service for creating users with secure password hashing and basic validation.
 */
public final class RegistrationService {

    private static final int USERNAME_MIN = 5;
    private static final int USERNAME_MAX = 256;
    private static final int PASSWORD_MIN = 6;
    private static final int PASSWORD_MAX = 256;

    private final UserDao userDao;
    private final PasswordHasher hasher;

    /**
     * Creates a registration service.
     *
     * @param userDao user DAO
     * @param hasher  password hasher
     */
    public RegistrationService(UserDao userDao, PasswordHasher hasher) {
        this.userDao = Objects.requireNonNull(userDao, "userDao");
        this.hasher = Objects.requireNonNull(hasher, "hasher");
    }

    private static String normalizeUsername(String u) {
        if (u == null) return null;
        String t = u.trim();
        return t.isEmpty() ? null : t;
    }

    private static String validate(String username, String password) {
        if (username == null) return "Missing username.";
        if (password == null) return "Missing password.";

        if (username.length() < USERNAME_MIN) return "Username too short (min " + USERNAME_MIN + ").";
        if (username.length() > USERNAME_MAX) return "Username too long (max " + USERNAME_MAX + ").";

        // Allow only a safe subset to avoid weird edge cases in UI and future.
        for (int i = 0; i < username.length(); i++) {
            char c = username.charAt(i);
            boolean ok = (c >= 'a' && c <= 'z')
                    || (c >= 'A' && c <= 'Z')
                    || (c >= '0' && c <= '9')
                    || c == '_' || c == '-' || c == '.';
            if (!ok) return "Username contains invalid characters.";
        }

        if (password.length() < PASSWORD_MIN) return "Password too short (min " + PASSWORD_MIN + ").";
        if (password.length() > PASSWORD_MAX) return "Password too long.";
        return null;
    }

    /**
     * Registers a new user.
     *
     * @param usernameRaw raw username (from form)
     * @param passwordRaw raw password (from form)
     * @return result containing either userId or an error message
     */
    public Result register(String usernameRaw, String passwordRaw) {
        String username = normalizeUsername(usernameRaw);
        String password = (passwordRaw == null) ? "" : passwordRaw;

        String validationError = validate(username, password);
        if (validationError != null) {
            return Result.error(validationError);
        }

        try {
            // Choose: store username as-is OR store sha256(username).
            // Your schema says: username(sha256 hex or plain) -> keep it plain for now.
            String usernameStored = username;

            if (userDao.findByUsername(usernameStored).isPresent()) {
                return Result.error("Username already exists.");
            }

            String passwordEncoded = hasher.hash(password);
            int userId = userDao.createUserWithNewUuid(usernameStored, passwordEncoded);

            return Result.ok(userId);
        } catch (Exception e) {
            return Result.error("Registration failed: " + e.getMessage());
        }
    }

    /**
     * Registration result.
     *
     * @param ok     whether succeeded
     * @param userId created user id, or -1
     * @param error  error message, or null
     */
    public record Result(boolean ok, int userId, String error) {

        /**
         * Creates a success result.
         *
         * @param userId user id
         * @return result
         */
        public static Result ok(int userId) {
            return new Result(true, userId, null);
        }

        /**
         * Creates an error result.
         *
         * @param error error message
         * @return result
         */
        public static Result error(String error) {
            return new Result(false, -1, error);
        }
    }
}