extension ConversationVC {
    
    final class ScrollToBottomButton : UIView {
        private let delegate: ScrollToBottomButtonDelegate
        
        // MARK: Settings
        private static let size: CGFloat = 40
        private static let iconSize: CGFloat = 16
        
        // MARK: Lifecycle
        init(delegate: ScrollToBottomButtonDelegate) {
            self.delegate = delegate
            super.init(frame: CGRect.zero)
            setUpViewHierarchy()
        }
        
        override init(frame: CGRect) {
            preconditionFailure("Use init(delegate:) instead.")
        }
        
        required init?(coder: NSCoder) {
            preconditionFailure("Use init(delegate:) instead.")
        }
        
        private func setUpViewHierarchy() {
            // Background & blur
            let backgroundView = UIView()
            backgroundView.backgroundColor = isLightMode ? .white : .black
            backgroundView.alpha = Values.lowOpacity
            addSubview(backgroundView)
            backgroundView.pin(to: self)
            let blurView = UIVisualEffectView(effect: UIBlurEffect(style: .regular))
            addSubview(blurView)
            blurView.pin(to: self)
            // Size & shape
            let size = ScrollToBottomButton.size
            set(.width, to: size)
            set(.height, to: size)
            layer.cornerRadius = size / 2
            layer.masksToBounds = true
            // Border
            layer.borderWidth = 1
            let borderColor = (isLightMode ? UIColor.black : UIColor.white).withAlphaComponent(Values.veryLowOpacity)
            layer.borderColor = borderColor.cgColor
            // Icon
            let tint = isLightMode ? UIColor.black : UIColor.white
            let icon = UIImage(named: "ic_chevron_down")!.withTint(tint)
            let iconImageView = UIImageView(image: icon)
            iconImageView.set(.width, to: ScrollToBottomButton.iconSize)
            iconImageView.set(.height, to: ScrollToBottomButton.iconSize)
            iconImageView.contentMode = .scaleAspectFit
            addSubview(iconImageView)
            iconImageView.center(in: self)
            // Gesture recognizer
            let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleTap))
            addGestureRecognizer(tapGestureRecognizer)
        }
        
        // MARK: Interaction
        @objc private func handleTap() {
            delegate.handleScrollToBottomButtonTapped()
        }
    }
}

protocol ScrollToBottomButtonDelegate {
    
    func handleScrollToBottomButtonTapped()
}