For @kadanas

//
// Created for ErrorAlert
// by Stewart Lynch on 2022-06-22
// Using Swift 5.0
//
// Follow me on Twitter: @StewartLynch
// Subscribe on YouTube: https://youTube.com/StewartLynch
//

import SwiftUI

struct ContentView: View {
    @StateObject private var viewModel = ViewModel()
    var body: some View {
        VStack {
            Text(viewModel.authenticationStatus)
            Button {
                try? viewModel.authenticate()
            } label: {
                Text("Login")
            }
            .buttonStyle(.borderedProminent)
        }
        .alert(item: $viewModel.alertString) { alertString in
            Alert(title: Text("Login Error"),
                  message: Text(alertString.errorString))
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}


class ViewModel: ObservableObject {
    @Published var authenticationStatus = "Please Log in"
    @Published var alertString: AlertString?

    
    enum AuthenticationError: Error {
        case failed
    }
    
    struct AlertString: Identifiable {
        let errorString: String
        var id: String {
            errorString
        }
    }
    
    func authenticate() throws {
        // This simulates a login that will sometimes fail.
        // If it is successful, it just updates the athenticationStatus property with that string
        // If it fails, it sets authenticationStatus to Try again but also sets the alertString
        // Published property to a non-optional instance of the AlertString struct and
        // The errorString property can then be used in your view for your alert Message
        // The key to this is to use the .alert(item:   ) constructor instead of the .alert(.isPresented: ) one
        // This one triggers every time an optional property is set (alertString?) and the alert will
        // then give you that instance of that property from which we can extract the errorString
        // And use it in the Alert.
        
        let random = Bool.random()
            if random {
                authenticationStatus = "Logged in Successfully"
            } else {
                authenticationStatus = "Try again"
                self.alertString = AlertString(errorString: "Login Failed")
                throw AuthenticationError.failed
            }
    }
}