How To - Using iOS to listen for events

import UIKit
import WebKit

//Class that handles iFrame display, response retrieval and decoding of the JSON response
class ViewController: UIViewController, WKUIDelegate, WKNavigationDelegate, WKScriptMessageHandler {
    var webView: WKWebView!
    
    //Global variables that are changed based on which merchant is creating a transaction
    var appid: String = "T6554252567241061980"
    var clientid: String = "01dffeb784c64d098c8c691ea589eb82"
    
    //Codable object that represents first level of response JSON object
    struct response: Codable {
        let event: String
        let data: Body
    }
    
    //Codable object that represents second level of response JSON object (is dependent on actual contents and will throw an error if field does not exist when decoding JSON)
    struct Body: Codable {
        let token: String
    }
    
    //View object that handles what is being displayed to screen
    override func loadView() {
        //Initial WebKit config and content controller creation
        let webConfiguration = WKWebViewConfiguration()
        let contentController = WKUserContentController()
        
        //JS script creation and setup for when in process of loading iFrame to inject script
        let js: String = "window.addEventListener('message', function(e){ window.webkit.messageHandlers.callbackHandler.postMessage(JSON.stringify(e.data)); });"
        let userScript = WKUserScript(source: js, injectionTime: WKUserScriptInjectionTime.atDocumentEnd, forMainFrameOnly: false)
        contentController.removeAllUserScripts()
        contentController.addUserScript(userScript)
        
        //Setup to allow for ContentController class to find and receive response as a result of JS script injection
        contentController.add(
            self,
            name: "callbackHandler"
        )
        webConfiguration.userContentController = contentController
        
        //Required calls to allow iFrame to be displayed on screen
        webView = WKWebView(frame: .zero, configuration: webConfiguration)
        webView.uiDelegate = self
        webView.navigationDelegate = self
        view = webView
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        //URL to iFrame initialization
        let myURL = URL(string: "https://secure.forms.qorcommerce.io/vault/card/token/?app_id=\(appid)&client_id=\(clientid)&profile_id=10203047&request_id=12345909&intent=create&cvv_field=true&button_text=Save%20Payment%20Method&textfield_type=filled")
        let myRequest = URLRequest(url: myURL!)
        
        //URL to iFrame loaded
        webView.load(myRequest)
    }
    
    //Function to handle the content being returned from iFrame JS script injection (in this case it is the JSON responses)
    func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        
        //Checking to see if message.body is not empty, and if so then setting a new variable as a String version of it
        if let bodyString = message.body as? String {
            //Converting new string as a Data object encoded as utf-8 which will allow for it to be decoded as JSON
            let body = Data(bodyString.utf8)
            do {
                //JSON decoder code using the Codable objects initialized at beginning of file
                let jsonResponse: response = try JSONDecoder().decode(response.self, from: body)
                //Checks the "event" field which coincides with the JSON response type received
                if (jsonResponse.event == "success_response") {
                    //Calls PopUpWindow class created in another swift file and displays the token that is created and returned from iFrame
                    //Note: Extra swift file is simply the popup window initializer that contains all the configurations desired such as size, colors and what information it contains for example
                    var popUpWindow: PopUpWindow!
                    popUpWindow = PopUpWindow(title: "Payment Token", text: "\(jsonResponse.data.token)", buttontext: "OK")
                    self.present(popUpWindow, animated: true, completion: nil)
                }
            //Used to catch errors thrown that include JSON encode/decode problems
            } catch {
                //Will print error only to the console of application in Xcode and not to the actual screen
                print(error)
            }
        }
        
    }

}

import SwiftUI
import WebKit

//Global variable to hold response token id
var token = ""

//Global variables that are changed based on which merchant is creating a transaction
var appid: String = "T6554252567241061980"
var clientid: String = "01dffeb784c64d098c8c691ea589eb82"

//Codable object that represents first level of response JSON object
struct response: Codable {
    let event: String
    let data: Body
}

//Codable object that represents second level of response JSON object (is dependent on actual contents and will throw an error if field does not exist when decoding JSON)
struct Body: Codable {
    let token: String
}

//View object that handles what is being displayed to screen
struct ContentView: View {
    
    //State variable that allows for Alert to toggle on and off
    @State private var showingAlert = false
        
    var body: some View {
        //Class that handles all JS iFrame needs
        WebView()
        //Example of a UI popup to show the resulting token from tokenization response
        .alert(isPresented: $showingAlert) {
            Alert(title: Text("Response Token"), message: Text("\(token)"), dismissButton: .default(Text("OK")))
        }
        .onReceive(NotificationCenter.default.publisher(for: WebView.showAlertMsg)) { msg in
            self.showingAlert = true // simply change the state of the View
        }
    }
}

//Class that handles calling JS iFrame and injecting JS script to get response back from tokenization process
struct WebView: UIViewRepresentable {
    
    //Static variable that is used when sending a notification to listener in the ContentView to create our example popup
    static let showAlertMsg = Notification.Name("ALERT_MSG")
    
    //Function that sets up WebKit config to handle JS script injection and content controller
    func makeUIView(context: Context) -> WKWebView {
        //Initial WebKit config and content controller creation
        let webConfiguration = WKWebViewConfiguration()
        let wkcontentController = WKUserContentController()
        
        //JS script creation and setup for when in process of loading iFrame to inject script
        let js: String = "window.addEventListener('message', function(e){ window.webkit.messageHandlers.callbackHandler.postMessage(JSON.stringify(e.data)); });"
        let userScript = WKUserScript(source: js, injectionTime: WKUserScriptInjectionTime.atDocumentEnd, forMainFrameOnly: false)
        wkcontentController.addUserScript(userScript)
        
        //Setup to allow for ContentController class to find and receive response as a result of JS script injection
        wkcontentController.add(context.coordinator, name: "callbackHandler")
        webConfiguration.userContentController = wkcontentController
        
        //Required calls to allow iFrame to be displayed on screen
        let webView = WKWebView(frame: .zero, configuration: webConfiguration)
        context.coordinator.parent = webView
        
        return webView
    }
    
    func updateUIView(_ uiView: WKWebView, context: Context) {
        //URL to iFrame initialization
        let request = URLRequest(url: URL(string: "https://secure.forms.qorcommerce.io/vault/card/token/?app_id=\(appid)&client_id=\(clientid)&profile_id=10203047&request_id=12345909&intent=create&cvv_field=true&button_text=Save%20Payment%20Method&textfield_type=filled")!)
        
        //URL to iFrame loaded
        uiView.load(request)
    }
    
    //Function that allows ContentController to be handled by an iOS handler
    func makeCoordinator() -> ContentController {
        ContentController()
    }
    
    //Class that contains ContentController functionality
    class ContentController: NSObject, WKScriptMessageHandler {

        weak var parent: WKWebView?

        //Function to handle the content being returned from iFrame JS script injection (in this case it is the JSON responses)
        func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
            
            //Checking to see if message.body is not empty, and if so then setting a new variable as a String version of it
            if let bodyString = message.body as? String {
                //Converting new string as a Data object encoded as utf8 which will allow for it to be decoded as JSON
                let body = Data(bodyString.utf8)
                do {
                    //JSON decoder code using the Codable objects initialized at beginning of file
                    let jsonResponse: response = try JSONDecoder().decode(response.self, from: body)
                    //Checks the "event" field which coincides with the JSON response type received
                    if (jsonResponse.event == "success_response") {
                        //Set global "token" variable as the token found in JSON response
                        token = jsonResponse.data.token
                        //Send out notification so that the Alert created in ContentView knows to display itself on screen
                        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
                            NotificationCenter.default.post(name: WebView.showAlertMsg, object: nil)
                        }
                    }
                //Used to catch errors thrown that include JSON encode/decode problems
                } catch {
                    //Will print error only to the console of application in Xcode and not to the actual screen
                    print(error)
                }
            }
        }
    }

}