ViewController using JavaScript

JSViewController.swift

import UIKit
import JavaScriptCore

class JSViewController: UIViewController {

    @IBOutlet weak var vPluginContainer: UIView!

    let jsContext = JSContext()!
    var timer: Timer? = nil

    let updateProperty: @convention(block) (Int, String, Any) -> Void = { tag, property, value in
        NotificationCenter.default.post(name: NSNotification.Name("updateWidgetProperty"), object: (tag, property, value))
    }

    let addWidget: @convention(block) (String, [String: Any]) -> Void = { widgetName, widgetProperties in
        print("Creating \(widgetName) with properties \(widgetProperties)")

        switch widgetName {
        case "Circle":
            guard let x = widgetProperties["x"] as? Double, 
                  let y = widgetProperties["y"] as? Double,
                  let r = widgetProperties["radius"] as? Double else {
                break
            }
            let color = widgetProperties["color"] as? String ?? "#ffffff"
            let tag = widgetProperties["tag"] as? Int ?? 0
            let v = UIView(frame: CGRect(x: x - r, y: y - r, width: r * 2, height: r * 2))
            v.layer.cornerRadius = CGFloat(r)
            v.tag = tag
            let uiColor = UIColor(hex: color) ?? .black
            v.backgroundColor = uiColor
            NotificationCenter.default.post(name: NSNotification.Name("addWidget"), object: v)
            break

        default:
            print("Unknown widget - \(widgetName)")
        }
    }

    @objc func addWidget(notification: NSNotification) {
        guard let w = notification.object as? UIView else { return }
        self.vPluginContainer.addSubview(w)
    }

    @objc func updateWidgetProperty(notification: NSNotification) {
        guard let attr = notification.object as? (tag: Int, property: String, value: Any) else { return }
        guard let w = vPluginContainer.viewWithTag(attr.tag) else { return }

        switch attr.property {
        case "color":
            if let strValue = attr.value as? String,
                let color = UIColor(hex: strValue) {
                w.backgroundColor = color
            }

        default:
            break
        }
    }

    private func loadJavaScript() {
        NotificationCenter.default.addObserver(self, selector: #selector(addWidget(notification:)), name: NSNotification.Name("addWidget"), object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(updateWidgetProperty(notification:)), name: NSNotification.Name("updateWidgetProperty"), object: nil)

        // Add an exception handler.
        jsContext.exceptionHandler = { _, exception in
            print("JS Exception: ", exception?.toString() ?? "Unknown")
        }

        guard let jsSourcePath = Bundle.main.path(forResource: "jsPluginCode", ofType: "js") else {
            print("JS file not found")
            return
        }
        
        do {
            let jsCode = try String(contentsOfFile: jsSourcePath)
            jsContext.evaluateScript(jsCode)

            let addWidgetObject = unsafeBitCast(self.addWidget, to: ViewController.self)
            jsContext.setObject(addWidgetObject, forKeyedSubscript: "addWidget" as NSString)
            let updatePropertyObject = unsafeBitCast(self.updateProperty, to: ViewController.self)
            jsContext.setObject(updatePropertyObject, forKeyedSubscript: "updateProperty" as NSString)
        }
        catch {
            print(error.localizedDescription)
        }
    }

    @IBAction func runPlugin() {
        loadJavaScript()

        let startFunction = jsContext.objectForKeyedSubscript("start")
        startFunction?.call(withArguments: [vPluginContainer.bounds.width, vPluginContainer.bounds.height])

        timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(tick), userInfo: nil, repeats: true)
    }

    @objc func tick() {
        let tickFunction = jsContext.objectForKeyedSubscript("tick")
        tickFunction?.call(withArguments: [10.0])
    }

}