@IBDesignable
class RevealView: UIView {

    var contentHeight: CGFloat = 300

    @IBInspectable var title: String = "" {
        didSet {
            titleLabel.text = title
        }
    }

    @IBInspectable var titleColor: UIColor = .lightGray {
        didSet {
            titleLabel.textColor = titleColor
        }
    }

    lazy var toggleExpandButton: UIButton = {
        let button = UIButton(type: .custom)
        button.tintColor = .black
        button.setTitleColor(.black, for: .normal)
        button.setTitle("Show less", for: .normal)
        button.titleLabel?.font = UIFont.systemFont(ofSize: 14.0)
        button.translatesAutoresizingMaskIntoConstraints = false
        return button
    }()

    lazy var footerView: UIView = {
        let view = UIView()
        view.translatesAutoresizingMaskIntoConstraints = false
        view.backgroundColor = .white
        view.clipsToBounds = true
        return view
    }()

    lazy var contentView: UIView = {
        let view = UIView()
        view.translatesAutoresizingMaskIntoConstraints = false
        view.backgroundColor = .lightGray
        return view
    }()

    lazy var titleLabel: UILabel = {
        let label = UILabel()
        label.textColor = .lightGray
        label.font = UIFont.boldSystemFont(ofSize: 18.0)
        label.numberOfLines = 1
        label.translatesAutoresizingMaskIntoConstraints = false
        return label
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupViews()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override func awakeFromNib() {
        setupViews()
    }

    override func prepareForInterfaceBuilder() {
        super.prepareForInterfaceBuilder()
        toggleExpandButton.setTitle("View less", for: .normal)
    }

    func compressingConstant(for subview: UIView) -> CGFloat {
        let footerHeight = footerView.frame.height
        let origin = subview.alignmentRect(forFrame: subview.frame).origin
        let originPoint = contentView.convert(origin, to: self)
        return originPoint.y + footerHeight
    }

    private func setupViews() {
        clipsToBounds = true
        addSubview(titleLabel)
        addSubview(contentView)
        addSubview(footerView)
        footerView.addSubview(toggleExpandButton)

        NSLayoutConstraint.activate([
            footerView.bottomAnchor.constraint(equalTo: bottomAnchor),
            footerView.rightAnchor.constraint(equalTo: rightAnchor),
            footerView.leftAnchor.constraint(equalTo: leftAnchor),
            footerView.heightAnchor.constraint(equalToConstant: 35),
            ])

        NSLayoutConstraint.activate([
            toggleExpandButton.heightAnchor.constraint(equalTo: footerView.heightAnchor),
            toggleExpandButton.centerYAnchor.constraint(equalTo: footerView.centerYAnchor),
            toggleExpandButton.rightAnchor.constraint(equalTo: footerView.rightAnchor, constant: -10.0),
            ])

        NSLayoutConstraint.activate([
            titleLabel.topAnchor.constraint(equalTo: topAnchor, constant: 16.0),
            titleLabel.leftAnchor.constraint(equalTo: leftAnchor, constant: 8.0),
            titleLabel.rightAnchor.constraint(equalTo: rightAnchor, constant: -8.0),
            ])

        NSLayoutConstraint.activate([
            contentView.topAnchor.constraint(equalTo: titleLabel.bottomAnchor, constant: 16.0),
            contentView.rightAnchor.constraint(equalTo: rightAnchor, constant: -8.0),
            contentView.leftAnchor.constraint(equalTo: leftAnchor, constant: 8.0),
            contentView.heightAnchor.constraint(equalToConstant: contentHeight)
            ])
    }

    override func layoutSubviews() {
        super.layoutSubviews()
        bringSubviewToFront(toggleExpandButton)
    }

}