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class StackViewController: UIViewController {
    private let scrollView = UIScrollView()
    private let stackView = UIStackView()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(scrollView)
        scrollView.addSubview(stackView)
        setupConstraints()
        stackView.axis = .vertical
    }

    private func setupConstraints() {
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        stackView.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate([
            scrollView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
            scrollView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
            scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
            scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
            stackView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor),
            stackView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor),
            stackView.topAnchor.constraint(equalTo: scrollView.topAnchor),
            stackView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor),
            stackView.widthAnchor.constraint(equalTo: view.safeAreaLayoutGuide.widthAnchor)
            ])
    }
}

extension StackViewController {
    func add(_ child: UIViewController) {
        addChild(child)
        stackView.addArrangedSubview(child.view)
        child.didMove(toParent: self)
    }

    func remove(_ child: UIViewController) {
        guard child.parent != nil else {
            return
        }

        child.willMove(toParent: nil)
        stackView.removeArrangedSubview(child.view)
        child.view.removeFromSuperview()
        child.removeFromParent()
    }
}

// Usage example:

class DayViewController: StackViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        setupUI()
    }

    private func setupUI() {
        let today = Date()
        let calendarVC = CalendarViewController(date: today)
        calendarVC.delegate = self

        add(calendarVC)
        add(SummaryViewController(date: today))
        add(SleepViewController(date: today))
        add(WorkoutViewController(date: today))
    }
}

extension DayViewController: CalendarViewControllDelegate {
    func dateSelected(_ date: Date) {
        reloadDay(with: date)
    }
}