using Inversion;
using Invercargill.DataStructures;

namespace Spry.Authentication {

    /**
     * Error domain for user-related operations.
     */
    public errordomain UserError {
        USER_NOT_FOUND,
        DUPLICATE_USERNAME,
        DUPLICATE_EMAIL,
        INVALID_PASSWORD,
        INVALID_CREDENTIALS,
        USER_INACTIVE,
        PERMISSION_DENIED,
        STORAGE_ERROR
    }

    /**
     * UserService provides user management operations including CRUD,
     * password hashing, and authentication.
     * 
     * This service uses the inject<> pattern for dependency injection.
     * All methods are async to work with the repository async API.
     */
    public class UserService : GLib.Object {

        private UserRepository _repository = inject<UserRepository>();

        // =========================================================================
        // User Creation
        // =========================================================================

        /**
         * Creates a new user with the specified credentials.
         *
         * This method:
         * - Validates username uniqueness
         * - Validates email uniqueness
         * - Hashes password with Argon2id via libsodium
         * - Creates User with UUID and timestamps
         *
         * @param username The unique username
         * @param email The unique email address
         * @param password The plaintext password to hash
         * @return The created User
         * @throws UserError on validation or storage failure
         */
        public async User create_user_async(string username, string email, string password) throws Error {
            // Validate username uniqueness
            if (yield username_exists_async(username)) {
                throw new UserError.DUPLICATE_USERNAME("Username already exists");
            }

            // Validate email uniqueness
            if (yield email_exists_async(email)) {
                throw new UserError.DUPLICATE_EMAIL("Email already exists");
            }

            // Hash password with Argon2id
            var password_hash = hash_password(password);
            if (password_hash == null) {
                throw new UserError.STORAGE_ERROR("Failed to hash password");
            }

            // Create user via repository
            var user = yield _repository.create(username, email, (!)password_hash);

            return user;
        }

        // =========================================================================
        // User Retrieval
        // =========================================================================

        /**
         * Gets a user by their unique ID.
         *
         * @param user_id The user's unique identifier
         * @return The User, or null if not found
         * @throws Error on storage failure
         */
        public async User? get_user_async(string user_id) throws Error {
            return yield _repository.get_by_id(user_id);
        }

        /**
         * Gets a user by their username.
         *
         * @param username The username to look up
         * @return The User, or null if not found
         * @throws Error on storage failure
         */
        public async User? get_user_by_username_async(string username) throws Error {
            return yield _repository.get_by_username(username);
        }

        /**
         * Gets a user by their email address.
         *
         * @param email The email address to look up
         * @return The User, or null if not found
         * @throws Error on storage failure
         */
        public async User? get_user_by_email_async(string email) throws Error {
            return yield _repository.get_by_email(email);
        }

        // =========================================================================
        // User Update
        // =========================================================================

        /**
         * Updates an existing user.
         *
         * This method:
         * - Updates the updated_at timestamp
         * - Handles username/email changes with uniqueness validation
         *
         * @param user The user to update
         * @throws Error on validation or storage failure
         */
        public async void update_user_async(User user) throws Error {
            // Get existing user to check for changes
            var existing = yield get_user_async(user.id);
            if (existing == null) {
                throw new UserError.USER_NOT_FOUND("User not found");
            }

            // Check if username changed
            if (existing.username != user.username) {
                // Check new username uniqueness
                var existing_with_username = yield get_user_by_username_async(user.username);
                if (existing_with_username != null && existing_with_username.id != user.id) {
                    throw new UserError.DUPLICATE_USERNAME("Username already exists");
                }
            }

            // Check if email changed
            if (existing.email != user.email) {
                // Check new email uniqueness
                var existing_with_email = yield get_user_by_email_async(user.email);
                if (existing_with_email != null && existing_with_email.id != user.id) {
                    throw new UserError.DUPLICATE_EMAIL("Email already exists");
                }
            }

            // Update timestamp
            user.updated_at = new DateTime.now_utc();

            // Store updated user via repository
            yield _repository.update(user);
        }

        // =========================================================================
        // User Deletion
        // =========================================================================

        /**
         * Deletes a user by their unique ID.
         *
         * @param user_id The user's unique identifier
         * @throws Error on storage failure
         */
        public async void delete_user_async(string user_id) throws Error {
            // Get user first (optional, for logging/cleanup)
            var user = yield get_user_async(user_id);
            if (user == null) {
                throw new UserError.USER_NOT_FOUND("User not found");
            }

            // Delete user via repository
            yield _repository.delete(user_id);
        }

        // =========================================================================
        // User Listing
        // =========================================================================

        /**
         * Lists users with pagination support.
         *
         * Note: This method is not supported by the basic UserRepository interface.
         * Subclasses or extensions should implement this as needed.
         *
         * @param offset The number of users to skip
         * @param limit The maximum number of users to return
         * @return A Vector of users
         * @throws Error on storage failure
         */
        public async Vector<User> list_users_async(int offset = 0, int limit = 100) throws Error {
            // The basic UserRepository interface doesn't include list operations
            // This would need to be added to the interface or handled differently
            // For now, return an empty list as a placeholder
            return new Vector<User>();
        }

        // =========================================================================
        // Password Management
        // =========================================================================

        /**
         * Hashes a password using Argon2id via libsodium.
         *
         * @param password The plaintext password to hash
         * @return The hashed password string, or null on failure
         */
        public string? hash_password(string password) {
            return Sodium.PasswordHashing.hash(password);
        }

        /**
         * Verifies a password against a stored hash.
         *
         * @param user The user to verify against
         * @param password The plaintext password to verify
         * @return true if the password matches, false otherwise
         */
        public bool verify_password(User user, string password) {
            return Sodium.PasswordHashing.check(user.password_hash, password);
        }

        /**
         * Sets a new password for a user.
         *
         * @param user The user to update
         * @param new_password The new plaintext password
         * @throws Error on failure
         */
        public async void set_password_async(User user, string new_password) throws Error {
            var password_hash = hash_password(new_password);
            if (password_hash == null) {
                throw new UserError.STORAGE_ERROR("Failed to hash password");
            }

            user.password_hash = (!)password_hash;
            user.updated_at = new DateTime.now_utc();

            yield update_user_async(user);
        }

        // =========================================================================
        // Authentication
        // =========================================================================

        /**
         * Authenticates a user by username/email and password.
         *
         * This method:
         * - Looks up user by username or email
         * - Verifies the password
         * - Returns the user if valid
         *
         * @param username_or_email The username or email address
         * @param password The plaintext password
         * @return The authenticated User, or null if authentication failed
         * @throws Error on storage failure
         */
        public async User? authenticate_async(string username_or_email, string password) throws Error {
            // Try to find user by username first, then by email
            User? user = yield get_user_by_username_async(username_or_email);

            if (user == null) {
                user = yield get_user_by_email_async(username_or_email);
            }

            if (user == null) {
                return null;
            }

            // Verify password
            bool password_valid = verify_password(user, password);
            
            if (!password_valid) {
                return null;
            }

            return user;
        }

        // =========================================================================
        // Utility Methods
        // =========================================================================

        /**
         * Checks if a username already exists.
         *
         * @param username The username to check
         * @return true if the username exists
         * @throws Error on storage failure
         */
        public async bool username_exists_async(string username) throws Error {
            return yield _repository.exists_by_username(username);
        }

        /**
         * Checks if an email already exists.
         *
         * @param email The email to check
         * @return true if the email exists
         * @throws Error on storage failure
         */
        public async bool email_exists_async(string email) throws Error {
            return yield _repository.exists_by_email(email);
        }

        /**
         * Gets the total count of users.
         *
         * Note: This method is not supported by the basic UserRepository interface.
         * Subclasses or extensions should implement this as needed.
         *
         * @return The number of users
         * @throws Error on storage failure
         */
        public async int user_count_async() throws Error {
            // The basic UserRepository interface doesn't include count operations
            // This would need to be added to the interface or handled differently
            return 0;
        }

        // =========================================================================
        // Permission Operations
        // =========================================================================

        /**
         * Adds a permission to a user.
         *
         * @param user The user to add the permission to
         * @param permission The permission to add
         * @throws Error on storage failure
         */
        public async void add_permission_async(User user, string permission) throws Error {
            yield _repository.add_permission(user.id, permission);
        }

        /**
         * Removes a permission from a user.
         *
         * @param user The user to remove the permission from
         * @param permission The permission to remove
         * @throws Error on storage failure
         */
        public async void remove_permission_async(User user, string permission) throws Error {
            yield _repository.remove_permission(user.id, permission);
        }

        /**
         * Checks if a user has a specific permission.
         *
         * @param user The user to check
         * @param permission The permission to check
         * @return true if the user has the permission
         * @throws Error on storage failure
         */
        public async bool has_permission_async(User user, string permission) throws Error {
            return yield _repository.has_permission(user.id, permission);
        }

        /**
         * Gets all permissions for a user.
         *
         * @param user The user to get permissions for
         * @return A Vector of permission strings
         * @throws Error on storage failure
         */
        public async Vector<string> get_permissions_async(User user) throws Error {
            return yield _repository.get_permissions(user.id);
        }

        // =========================================================================
        // App Data Operations
        // =========================================================================

        /**
         * Sets an app data value for a user.
         *
         * @param user The user to set the app data for
         * @param key The app data key
         * @param value The app data value
         * @throws Error on storage failure
         */
        public async void set_app_data_async(User user, string key, string value) throws Error {
            yield _repository.set_app_data(user.id, key, value);
        }

        /**
         * Gets an app data value for a user.
         *
         * @param user The user to get the app data for
         * @param key The app data key
         * @return The app data value, or null if not found
         * @throws Error on storage failure
         */
        public async string? get_app_data_async(User user, string key) throws Error {
            return yield _repository.get_app_data(user.id, key);
        }
    }
}