add error alert

Cheetah/Views/AuthTokenView.swift

@@ -30,7 +30,7 @@ struct AuthTokenView: View {
     }
 }
 
-struct APIKeyView_Previews: PreviewProvider {
+struct AuthTokenView_Previews: PreviewProvider {
     static var previews: some View {
         return AuthTokenView(
             storedToken: Binding.constant(nil),

Cheetah/Views/CoachView.swift

@@ -7,6 +7,9 @@ struct CoachView: View {
     @State var answer: String
     @State var answerSelection = NSRange()
     
+    @State var showError = false
+    @State var errorDescription = ""
+    
     init(viewModel: AppViewModel) {
         self.viewModel = viewModel
         self.answer = viewModel.answer ?? ""
@@ -55,6 +58,17 @@ struct CoachView: View {
                 }
             }
         }
+        .onReceive(viewModel.$errorDescription) {
+            if let error = $0 {
+                self.showError = true
+                self.errorDescription = error
+            }
+        }
+        .alert(errorDescription, isPresented: $showError) {
+            Button("OK", role: .cancel) {
+                self.showError = false
+            }
+        }
         HStack {
             VStack(alignment: .leading, spacing: 20) {
                 if let transcript = viewModel.transcript {

Cheetah/Views/ContentView.swift

@@ -6,7 +6,7 @@ struct ContentView: View {
     
     @ViewBuilder
     var body: some View {
-        if viewModel.authToken != nil {
+        if viewModel.authToken?.isEmpty == false {
             VStack(spacing: 16) {
                 switch viewModel.downloadState {
                 case .pending: