/*

There are two related tasks with a common domain model:

Account (guid: UUID, balance: long)

User (login: String, account: Account)

Both classes have getters for all corresponding fields: getGuid(), getBalance(), getLogin(), getAccount().

You need to write a method findUserByLogin(String login) that returns an optional value of type Optional<User>.

If the user exists in the users set you need to return non-empty optional wrapping the user inside,

otherwise returned optional should be empty.

*/

private static final Set<User> users = new HashSet<>();

public static Optional<User> findUserByLogin(String login) {

return users.stream().filter(u -> login.equals(u.getLogin())).findAny();

}

/*

Using the method you wrote for finding an user by their login, write a new method

printBalanceIfNotEmpty(String userLogin)that prints an account balance for an existing user if `balance > 0`.

In this case, the result format should print the string:

login: balance

If the user is not found, account is null or the balance = 0, then the method should not print anything.

Do not forget to use optional for avoiding NPE.

*/

public static void printBalanceIfNotEmpty(String userLogin) {

findUserByLogin(userLogin)

.map(User::getAccount)

.map(Account::getBalance)

.filter(v -> v > 0)

.map(v -> new String(userLogin + ": " + v))

.ifPresent(System.out::println);

}