JSONRepresentable.swift

//: A UIKit based Playground for presenting user interface

import UIKit
import PlaygroundSupport


public struct Renderable {
    private let handle: () -> Void
    
    public init(_ handle: @escaping () -> Void) {
        self.handle = handle
    }
    
    func render() {
        handle()
    }
    
}


public typealias Configuration = [String: Any]

public protocol JSONRepresentable {
    var identifier: String { get }
    func render(with configuration: Configuration) -> Renderable
}

extension JSONRepresentable where Self: NSObject {
    
    public var identifier: String {
        return String(describing: Self.classForCoder())
    }
    
    public func render(with configuration: Configuration) -> Renderable {
        
        return Renderable {
            let myReflection = Mirror(reflecting: self)
            configuration.forEach { [myReflection] key, configuration in
                // if we can configure the property using KVC else use mirroring
                if Self.instancesRespond(to: Selector(key)) {
                    // For not straight forward keys like layer we need to perform it's render pass
                    if let element = self.value(forKey: key) as? JSONRepresentable,
                        let elementConfiguration = configuration as? Configuration {
                        element.render(with: elementConfiguration).render()
                    } else {
                        self.setValue(configuration, forKeyPath: key)
                    }
                } else {
                    // There can't be two properties with same name, so taking the first one
                    if let property = myReflection.children.filter({ $0.label == key }).first {
                        if let renderable = property.value as? JSONRepresentable,
                            let elementConfiguration = configuration as? Configuration {
                            renderable.render(with: elementConfiguration).render()
                        }
                    } else {
                        print("Invalid '\(key)' key found while rendering \(self.identifier)")
                    }
                }
            }
        }
    }
}

extension CALayer: JSONRepresentable {}
extension UILabel: JSONRepresentable {}

class TestView: UIView, JSONRepresentable {
    var titleLabel = UILabel()
    var subtitleLabel = UILabel()
    override init(frame: CGRect) {
        super.init(frame: frame)
        addSubview(titleLabel)
        addSubview(subtitleLabel)
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        titleLabel.frame = CGRect(origin: .zero, size: .init(width: 144, height: 44))
        subtitleLabel.frame = CGRect(origin: .init(x: 0, y: 46), size: .init(width: 144, height: 44))
    }
    
    required init?(coder aDecoder: NSCoder) {
        return nil
    }
    
}
let view = TestView(frame: .init(origin: .zero, size: .init(width: 144, height: 144)))

view.backgroundColor = .red

let testViewRenderable = view.render(with: [
    "backgroundColor": UIColor.darkGray,
    "titleLabel": [
        "text": "Hello",
        "textAlignment": NSTextAlignment.center.rawValue,
        "numberOfLines": 1,
        "textColor": UIColor.white,
        "layer": [
            "borderColor": UIColor.blue.cgColor,
            "borderWidth": 2
        ]
    ],
    "subtitleLabel": [
        "text": "World",
        "textAlignment": NSTextAlignment.center.rawValue,
        "numberOfLines": 1,
        "textColor": UIColor.white,
        "layer": [
            "borderColor": UIColor.blue.cgColor,
            "borderWidth": 2
        ]
    ],
    "layer": [
        "cornerRadius": 5,
        "borderWidth": 1,
        "borderColor": UIColor.red.cgColor
    ]
])

PlaygroundPage.current.liveView = view
testViewRenderable.render()
PlaygroundPage.current.needsIndefiniteExecution = true