Make embedded confirm handle in-flight and failed update calls. (#4174)

Previous PR: #4168

Still to come:

- Restore previous customer input in form (2) + E2E tests (e.g. load PI
-> fill out card form -> update to SI -> expect form to be preserved but
w/o checkbox)
- (Bonus) Cancel network calls etc. from previous update to reduce
battery/network usage. Can apply this to FC.update as well.

## Motivation
https://jira.corp.stripe.com/browse/MOBILESDK-2583

## Testing
See unit tests

## Changelog
Not user facing

Example/PaymentSheet Example/PaymentSheetUITest/XCUITest+Utilities.swift

@@ -285,23 +285,30 @@ extension XCTestCase {
     }
 
     func waitForReload(_ app: XCUIApplication, settings: PaymentSheetTestPlaygroundSettings) {
-        if settings.uiStyle == .paymentSheet {
+        switch settings.uiStyle {
+        case .paymentSheet:
             let presentButton = app.buttons["Present PaymentSheet"]
             expectation(
                 for: NSPredicate(format: "enabled == true"),
                 evaluatedWith: presentButton,
                 handler: nil
             )
-            waitForExpectations(timeout: 10, handler: nil)
-        } else {
+        case .flowController:
             let confirm = app.buttons["Confirm"]
             expectation(
                 for: NSPredicate(format: "enabled == true"),
                 evaluatedWith: confirm,
                 handler: nil
             )
-            waitForExpectations(timeout: 10, handler: nil)
+        case .embedded:
+            let confirm = app.buttons["Present embedded payment element"]
+            expectation(
+                for: NSPredicate(format: "enabled == true"),
+                evaluatedWith: confirm,
+                handler: nil
+            )
         }
+        waitForExpectations(timeout: 10, handler: nil)
     }
     func loadPlayground(_ app: XCUIApplication, _ settings: PaymentSheetTestPlaygroundSettings) {
         if #available(iOS 15.0, *) {

StripePaymentSheet/StripePaymentSheet/Source/PaymentSheet/Embedded/EmbeddedPaymentElement.swift

@@ -164,8 +164,25 @@ public final class EmbeddedPaymentElement {
     /// Completes the payment or setup.
     /// - Returns: The result of the payment after any presented view controllers are dismissed.
     /// - Note: This method presents authentication screens on the instance's  `presentingViewController` property.
+    /// - Note: This method requires that the last call to `update` succeeded. If the last `update` call failed, this call will fail. If this method is called while a call to `update` is in progress, it waits until the `update` call completes.
     public func confirm() async -> EmbeddedPaymentElementResult {
-        // TODO
+        // Wait for the last update to finish and fail if didn't succeed. A failure means the view is out of sync with the intent and could e.g. not be showing a required mandate.
+        if let currentUpdateTask {
+            switch await currentUpdateTask.value {
+            case .succeeded:
+                // The view is in sync with the intent. Continue on with confirm!
+                break
+            case .failed(error: let error):
+                return .failed(error: error)
+            case .canceled:
+                let errorMessage = "confirm was called when the current update task is canceled. This shouldn't be possible; the current update task should only cancel if another task began."
+                stpAssertionFailure(errorMessage)
+                let error = PaymentSheetError.flowControllerConfirmFailed(message: errorMessage)
+                let errorAnalytic = ErrorAnalytic(event: .unexpectedPaymentSheetError, error: error)
+                STPAnalyticsClient.sharedClient.log(analytic: errorAnalytic)
+                return .failed(error: error)
+            }
+        }
         return .canceled
     }
 
@@ -286,6 +303,7 @@ extension EmbeddedPaymentElement {
     /// Completes the payment or setup.
     /// - Parameter completion: Called with the result of the payment after any presented view controllers are dismissed. Called on the mai thread.
     /// - Note: This method presents authentication screens on the instance's  `presentingViewController` property.
+    /// - Note: This method requires that the last call to `update` succeeded. If the last `update` call failed, this call will fail. If this method is called while a call to `update` is in progress, it waits until the `update` call completes.
     public func confirm(completion: @escaping (EmbeddedPaymentElementResult) -> Void) {
         Task {
             let result = await confirm()

StripePaymentSheet/StripePaymentSheet/Source/PaymentSheet/PaymentSheetFlowController.swift

@@ -341,12 +341,12 @@ extension PaymentSheet {
 
             switch latestUpdateContext?.status {
             case .inProgress:
-                assertionFailure("`confirmPayment` should only be called when the last update has completed.")
+                assertionFailure("`confirm` should only be called when the last update has completed.")
                 let error = PaymentSheetError.flowControllerConfirmFailed(message: "confirmPayment was called with an update API call in progress.")
                 completion(.failed(error: error))
                 return
             case .failed:
-                assertionFailure("`confirmPayment` should only be called when the last update has completed without error.")
+                assertionFailure("`confirm` should only be called when the last update has completed without error.")
                 let error = PaymentSheetError.flowControllerConfirmFailed(message: "confirmPayment was called when the last update API call failed.")
                 completion(.failed(error: error))
                 return
@@ -355,7 +355,7 @@ extension PaymentSheet {
             }
 
             guard let paymentOption = _paymentOption else {
-                assertionFailure("`confirmPayment` should only be called when `paymentOption` is not nil")
+                assertionFailure("`confirm` should only be called when `paymentOption` is not nil")
                 let error = PaymentSheetError.flowControllerConfirmFailed(message: "confirmPayment was called with a nil paymentOption")
                 completion(.failed(error: error))
                 return

StripePaymentSheet/StripePaymentSheetTests/PaymentSheet/EmbeddedPaymentElementTest.swift

@@ -134,6 +134,39 @@ class EmbeddedPaymentElementTest: XCTestCase {
         XCTAssertEqual(updateResult2, .succeeded)
         XCTAssertTrue(sut.loadResult.intent.isSettingUp)
     }
+
+    func testConfirmHandlesInflightUpdateThatSucceeds() async throws {
+        // Given a EmbeddedPaymentElement instance...
+        let sut = try await EmbeddedPaymentElement.create(intentConfiguration: paymentIntentConfig, configuration: configuration)
+        // ...updating...
+        async let _updateResult = sut.update(intentConfiguration: paymentIntentConfig)
+        // ...and immediately calling confirm, before the 1st update finishes...
+        let confirmResult = await sut.confirm()
+        // ...should make the confirm call wait for the update and then
+        switch confirmResult {
+        case .canceled: // TODO: When confirm works, change this to .completed
+            break
+        default:
+            XCTFail("Expected confirm to succeed")
+        }
+    }
+
+    func testConfirmHandlesInflightUpdateThatFails() async throws {
+        // Given a EmbeddedPaymentElement instance...
+        let sut = try await EmbeddedPaymentElement.create(intentConfiguration: paymentIntentConfig, configuration: configuration)
+        // ...updating w/ a broken config...
+        let brokenConfig = EmbeddedPaymentElement.IntentConfiguration(mode: .payment(amount: -1000, currency: "bad currency"), confirmHandler: { _, _, _ in })
+        async let _ = sut.update(intentConfiguration: brokenConfig)
+        // ...and immediately calling confirm, before the 1st update finishes...
+        async let confirmResult = sut.confirm() // Note: If this is `await`, it runs *before* the `update` call above is run.
+        // ...should make the confirm call wait for the update and then fail b/c the update failed
+        switch await confirmResult {
+        case let .failed(error: error):
+            XCTAssertEqual(error.nonGenericDescription.prefix(101), "An error occurred in PaymentSheet. The amount in `PaymentSheet.IntentConfiguration` must be non-zero!")
+        default:
+            XCTFail("Expected confirm to fail")
+        }
+    }
 }
 
 extension EmbeddedPaymentElementTest: EmbeddedPaymentElementDelegate {