StateView.swift

import UIKit
import GenericViewKit

public class StateView: GenericView {
    public enum State {
        case Loading
        case Loaded
        case Error
    }

    public var state: State = .Loading {
        didSet { didUpdateState() }
    }

    public var style: ContentStyle = .Dark {
        didSet {
            errorView.style = style
            activityIndicator.color = style.primaryColor
        }
    }

    public var minimumIntrinsicContentHeight: CGFloat = 0 {
        didSet { invalidateIntrinsicContentSize() }
    }

    public let errorView = ErrorView()
    
    public let contentView = UIView().then {
        $0.backgroundColor = .blackColor()
        $0.hidden = true
    }

    private let activityIndicator = (UIActivityIndicatorView(activityIndicatorStyle: .WhiteLarge).then {
        $0.hidesWhenStopped = true
    }

    public override func intrinsicContentSize() -> CGSize {
        let size: CGSize

        switch state {
        case .Loading: size = activityIndicator.intrinsicContentSize()
        case .Loaded: size = contentView.intrinsicContentSize()
        case .Error: size = errorView.intrinsicContentSize()
        }

        return CGSize(width: size.width, height: max(minimumIntrinsicContentHeight, size.height))
    }

    public override func configureView() {
        super.configureView()

        addSubview(contentView)
        addSubview(activityIndicator)
        addSubview(errorView)

        contentView.setEdgesEqualToSuperview()
        activityIndicator.setCenterInSuperview()

        errorView.setCenterInSuperview()
        errorView.setWidthEqual(self, multiplier: 2/3)

        didUpdateState()
        translatesAutoresizingMaskIntoConstraints = true
    }
    
    public func showError(message: String?) {
        let fallbackError = R.string.localizable.genericErrorSomethingWrong()
        errorView.errorLabel.text = message ?? fallbackError
        state = .Error
    }

    private func didUpdateState() {
        switch state {
        case .Loading:
            contentView.hidden = false
            errorView.hidden = true

            activityIndicator.startAnimating()
        case .Loaded:
            contentView.hidden = false
            errorView.hidden = true

            activityIndicator.stopAnimating()
        case .Error:
            contentView.hidden = true
            errorView.hidden = false

            activityIndicator.stopAnimating()
        }

        invalidateIntrinsicContentSize()
    }
}