transaction user_transactions_iterator::wait_next_transaction() noexcept {
    std::unique_lock ul(pointer_on_user_->user_mutex);
    pointer_on_user_->cond.wait(
        ul, [&]() { return size_ < pointer_on_user_->operations.size(); });
    return pointer_on_user_->operations[size_++];
}

user::user() = default;
user::user(const std::string &new_name)
    : user_name(new_name), balance(INITIAL_BALANCE) {
    std::unique_lock ul(user_mutex);
    operations.emplace_back(nullptr, INITIAL_BALANCE,
                            "Initial deposit for " + new_name);
    cond.notify_all();
}
[[nodiscard]] int user::balance_xts() const {
    std::unique_lock ul(user_mutex);
    return balance;
}

[[nodiscard]] std::string user::name() const noexcept {
    return user_name;
}

[[nodiscard]] user_transactions_iterator user::monitor() const noexcept {
    std::unique_lock ul(user_mutex);
    return user_transactions_iterator{operations.size(), this};
}