ContentView.swift

import SwiftUI

struct ContentView: View {
    @EnvironmentObject var twitterAPI: TwitterAPI // 1

    var body: some View {
        VStack {
            if let screenName = twitterAPI.user?.screenName { // 2
                Text("Welcome").font(.largeTitle)
                Text(screenName).font(.largeTitle)
            } else { // 3
                Button("Signin with Twitter", action: {
                    twitterAPI.authorize()
                })
            }
        }
        .sheet(isPresented: $twitterAPI.authorizationSheetIsPresented) { // 4
            SafariView(url: $twitterAPI.authorizationURL) // 5
        }
    }
}

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