final class KeyPairMigrationSheet : Sheet {

    override class var isDismissable: Bool { false }
    
    override func populateContentView() {
        // Image view
        let imageView = UIImageView(image: #imageLiteral(resourceName: "Shield").withTint(Colors.text))
        imageView.set(.width, to: 64)
        imageView.set(.height, to: 64)
        imageView.contentMode = .scaleAspectFit
        // Title label
        let titleLabel = UILabel()
        titleLabel.textColor = Colors.text
        titleLabel.font = .boldSystemFont(ofSize: isIPhone5OrSmaller ? Values.largeFontSize : Values.veryLargeFontSize)
        titleLabel.text = "Session IDs Just Got Better"
        titleLabel.textAlignment = .center
        titleLabel.numberOfLines = 0
        titleLabel.lineBreakMode = .byWordWrapping
        // Top stack view
        let topStackView = UIStackView(arrangedSubviews: [ imageView, titleLabel ])
        topStackView.axis = .vertical
        topStackView.spacing = Values.largeSpacing
        topStackView.alignment = .center
        // Explanation label
        let explanationLabel = UILabel()
        explanationLabel.textColor = Colors.text
        explanationLabel.font = .systemFont(ofSize: Values.smallFontSize)
        explanationLabel.textAlignment = .center
        explanationLabel.text = """
        We’ve upgraded Session IDs to make them even more private and secure. To ensure your continued privacy you're now required to upgrade.

        Your existing contacts and conversations will be lost, but you’ll be able to use Session knowing you have the best privacy and security possible.
        """
        explanationLabel.numberOfLines = 0
        explanationLabel.lineBreakMode = .byWordWrapping
        // Upgrade now button
        let upgradeNowButton = Button(style: .prominentOutline, size: .large)
        upgradeNowButton.set(.width, to: 240)
        upgradeNowButton.setTitle("Upgrade Now", for: UIControl.State.normal)
        upgradeNowButton.addTarget(self, action: #selector(upgradeNow), for: UIControl.Event.touchUpInside)
        // Upgrade now button
        let upgradeLaterButton = Button(style: .prominentOutline, size: .large)
        upgradeLaterButton.set(.width, to: 240)
        upgradeLaterButton.setTitle("Upgrade Later", for: UIControl.State.normal)
        upgradeLaterButton.addTarget(self, action: #selector(upgradeLater), for: UIControl.Event.touchUpInside)
        // Button stack view
        let buttonStackView = UIStackView(arrangedSubviews: [ upgradeNowButton, upgradeLaterButton ])
        buttonStackView.axis = .vertical
        buttonStackView.spacing = Values.mediumSpacing
        buttonStackView.alignment = .center
        // Main stack view
        let stackView = UIStackView(arrangedSubviews: [ topStackView, explanationLabel, buttonStackView ])
        stackView.axis = .vertical
        stackView.spacing = Values.veryLargeSpacing
        stackView.alignment = .center
        // Constraints
        contentView.addSubview(stackView)
        stackView.pin(.leading, to: .leading, of: contentView, withInset: Values.veryLargeSpacing)
        stackView.pin(.top, to: .top, of: contentView, withInset: Values.largeSpacing)
        contentView.pin(.trailing, to: .trailing, of: stackView, withInset: Values.veryLargeSpacing)
        contentView.pin(.bottom, to: .bottom, of: stackView, withInset: Values.veryLargeSpacing + overshoot)
    }
    
    @objc private func upgradeNow() {
        Storage.prepareForV2KeyPairMigration()
    }
    
    @objc private func upgradeLater() {
        let alert = UIAlertController(title: "Warning", message: "You won't be able to send or receive messages until you upgrade.", preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "OK", accessibilityIdentifier: nil, style: .default, handler: nil))
        presentingViewController?.dismiss(animated: true, completion: nil) // Dismiss self
        presentingViewController?.present(alert, animated: true, completion: nil)
    }
}