Improve error reporting for onboarding, use async/await

Tusker/Controllers/MastodonController.swift

@@ -67,29 +67,42 @@ class MastodonController: ObservableObject {
         return client.run(request, completion: completion)
     }
     
-    func registerApp(completion: @escaping (_ clientID: String, _ clientSecret: String) -> Void) {
+    /// - Returns: A tuple of client ID and client secret.
-        guard client.clientID == nil,
+    func registerApp() async throws -> (String, String) {
-            client.clientSecret == nil else {
+        if let clientID = client.clientID,
-                
+           let clientSecret = client.clientSecret {
-                completion(client.clientID!, client.clientSecret!)
+            return (clientID, clientSecret)
-                return
+        } else {
-        }
+            let app: RegisteredApplication = try await withCheckedThrowingContinuation({ continuation in
-
                 client.registerApp(name: "Tusker", redirectURI: "tusker://oauth", scopes: [.read, .write, .follow]) { response in
-            guard case let .success(app, _) = response else { fatalError() }
+                    switch response {
+                    case .failure(let error):
+                        continuation.resume(throwing: error)
+                    case .success(let app, _):
+                        continuation.resume(returning: app)
+                    }
+                }
+            })
             self.client.clientID = app.clientID
             self.client.clientSecret = app.clientSecret
-            completion(app.clientID, app.clientSecret)
+            return (app.clientID, app.clientSecret)
         }
     }
     
-    func authorize(authorizationCode: String, completion: @escaping (_ accessToken: String) -> Void) {
+    /// - Returns: The access token
+    func authorize(authorizationCode: String) async throws -> String {
+        return try await withCheckedThrowingContinuation({ continuation in
             client.getAccessToken(authorizationCode: authorizationCode, redirectURI: "tusker://oauth") { response in
-            guard case let .success(settings, _) = response else { fatalError() }
+                switch response {
+                case .failure(let error):
+                    continuation.resume(throwing: error)
+                case .success(let settings, _):
                     self.client.accessToken = settings.accessToken
-            completion(settings.accessToken)
+                    continuation.resume(returning: settings.accessToken)
                 }
             }
+        })
+    }
     
     func getOwnAccount(completion: ((Result<Account, Client.Error>) -> Void)? = nil) {
         if account != nil {
@@ -120,6 +133,18 @@ class MastodonController: ObservableObject {
         }
     }
     
+    func getOwnAccount() async throws -> Account {
+        if let account = account {
+            return account
+        } else {
+            return try await withCheckedThrowingContinuation({ continuation in
+                self.getOwnAccount { result in
+                    continuation.resume(with: result)
+                }
+            })
+        }
+    }
+    
     func getOwnInstance(completion: ((Instance) -> Void)? = nil) {
         getOwnInstanceInternal(retryAttempt: 0, completion: completion)
     }

Tusker/Screens/Onboarding/OnboardingViewController.swift

@@ -8,8 +8,10 @@
 
 import UIKit
 import AuthenticationServices
+import Pachyderm
 
 protocol OnboardingViewControllerDelegate {
+    @MainActor
     func didFinishOnboarding(account: LocalData.UserAccountInfo)
 }
 
@@ -41,13 +43,43 @@ class OnboardingViewController: UINavigationController {
         instanceSelector.delegate = self
     }
     
-}
+    @MainActor
-
+    private func tryLoginTo(instanceURL: URL) async throws {
-extension OnboardingViewController: InstanceSelectorTableViewControllerDelegate {
-    func didSelectInstance(url instanceURL: URL) {
         let mastodonController = MastodonController(instanceURL: instanceURL)
-        mastodonController.registerApp { (clientID, clientSecret) in
+        let clientID: String
+        let clientSecret: String
+        do {
+            (clientID, clientSecret) = try await mastodonController.registerApp()
+        } catch {
+            throw Error.registeringApp(error)
+        }
+        let authCode = try await getAuthorizationCode(instanceURL: instanceURL, clientID: clientID)
+        let accessToken: String
+        do {
+            accessToken = try await mastodonController.authorize(authorizationCode: authCode)
+        } catch {
+            throw Error.gettingAccessToken(error)
+        }
         
+        // construct a temporary UserAccountInfo instance for the MastodonController to use to fetch its own account
+        let tempAccountInfo = LocalData.UserAccountInfo(id: "temp", instanceURL: instanceURL, clientID: clientID, clientSecret: clientSecret, username: nil, accessToken: accessToken)
+        mastodonController.accountInfo = tempAccountInfo
+        
+        let ownAccount: Account
+        do {
+            ownAccount = try await mastodonController.getOwnAccount()
+        } catch {
+            throw Error.gettingOwnAccount(error)
+        }
+        
+        let accountInfo = LocalData.shared.addAccount(instanceURL: instanceURL, clientID: clientID, clientSecret: clientSecret, username: ownAccount.username, accessToken: accessToken)
+        mastodonController.accountInfo = accountInfo
+        
+        self.onboardingDelegate?.didFinishOnboarding(account: accountInfo)
+    }
+    
+    @MainActor
+    private func getAuthorizationCode(instanceURL: URL, clientID: String) async throws -> String {
         var components = URLComponents(url: instanceURL, resolvingAgainstBaseURL: false)!
         components.path = "/oauth/authorize"
         components.queryItems = [
@@ -58,42 +90,62 @@ extension OnboardingViewController: InstanceSelectorTableViewControllerDelegate
         ]
         let authorizeURL = components.url!
         
-            self.authenticationSession = ASWebAuthenticationSession(url: authorizeURL, callbackURLScheme: "tusker") { url, error in
+        return try await withCheckedThrowingContinuation({ continuation in
-                guard error == nil,
+            self.authenticationSession = ASWebAuthenticationSession(url: authorizeURL, callbackURLScheme: "tusker", completionHandler: { url, error in
-                    let url = url,
+                if let error = error {
+                    continuation.resume(throwing: Error.authenticationSessionError(error))
+                } else if let url = url,
                           let components = URLComponents(url: url, resolvingAgainstBaseURL: true),
                           let item = components.queryItems?.first(where: { $0.name == "code" }),
-                    let authCode = item.value else { return }
+                          let code = item.value {
-                
+                    continuation.resume(returning: code)
-                mastodonController.authorize(authorizationCode: authCode) { (accessToken) in
+                } else {
-                    // construct a temporary UserAccountInfo instance for the MastodonController to use to fetch it's own account
+                    continuation.resume(throwing: Error.noAuthorizationCode)
-                    let tempAccountInfo = LocalData.UserAccountInfo(id: "temp", instanceURL: instanceURL, clientID: clientID, clientSecret: clientSecret, username: nil, accessToken: accessToken)
-                    mastodonController.accountInfo = tempAccountInfo
-                    
-                    mastodonController.getOwnAccount { (result) in
-                        DispatchQueue.main.async {
-                            switch result {
-                            case let .failure(error):
-                                let alert = UIAlertController(title: "Unable to Verify Credentials", message: "Your account could not be fetched at this time: \(error.localizedDescription)", preferredStyle: .alert)
-                                alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
-                                self.present(alert, animated: true)
-                                
-                            case let .success(account):
-                                // this needs to happen on the main thread because it publishes a new value for the ObservableObject
-                                let accountInfo = LocalData.shared.addAccount(instanceURL: instanceURL, clientID: clientID, clientSecret: clientSecret, username: account.username, accessToken: accessToken)
-                                mastodonController.accountInfo = accountInfo
-                                
-                                self.onboardingDelegate?.didFinishOnboarding(account: accountInfo)
                 }
-                        }
+            })
-                    }
-                }
-            }
-            DispatchQueue.main.async {
             // Prefer ephemeral sessions to make it easier to sign into multiple accounts on the same instance.
             self.authenticationSession!.prefersEphemeralWebBrowserSession = true
             self.authenticationSession!.presentationContextProvider = self
             self.authenticationSession!.start()
+        })
+    }
+
+}
+
+extension OnboardingViewController {
+    enum Error: Swift.Error {
+        case registeringApp(Swift.Error)
+        case authenticationSessionError(Swift.Error)
+        case noAuthorizationCode
+        case gettingAccessToken(Swift.Error)
+        case gettingOwnAccount(Swift.Error)
+        
+        var localizedDescription: String {
+            switch self {
+            case .registeringApp(let error):
+                return "Couldn't register app: \(error)"
+            case .authenticationSessionError(let error):
+                return error.localizedDescription
+            case .noAuthorizationCode:
+                return "No authorization code"
+            case .gettingAccessToken(let error):
+                return "Couldn't get access token: \(error)"
+            case .gettingOwnAccount(let error):
+                return "Couldn't fetch account: \(error)"
+            }
+        }
+    }
+}
+
+extension OnboardingViewController: InstanceSelectorTableViewControllerDelegate {
+    func didSelectInstance(url instanceURL: URL) {
+        Task {
+            do {
+                try await self.tryLoginTo(instanceURL: instanceURL)
+            } catch let error as Error {
+                let alert = UIAlertController(title: "Error Logging In", message: error.localizedDescription, preferredStyle: .alert)
+                alert.addAction(UIAlertAction(title: "Ok", style: .default))
+                self.present(alert, animated: true)
             }
         }
     }