Merge pull request #5303 from woocommerce/issue/4911-minimum-amount

[Mobile Payments] Cancel payment capture if order amount is below minimum (USD only)

Author: ctarda

Hardware/Hardware/CardReader/CardReaderServiceError.swift

@@ -186,6 +186,9 @@ public enum UnderlyingError: Error {
     /// The SDK will attempt to auto-disconnect for you and you should instruct your user to reconnect it.
     case readerSessionExpired
 
+    /// The underlying request returned an API error.
+    case processorAPIError
+
     /// Catch-all error case. Indicates there is something wrong with the
     /// internal state of the CardReaderService.
     case internalServiceError
@@ -305,6 +308,9 @@ updating the application or using a different reader
         case .readerSessionExpired:
             return NSLocalizedString("The card reader session has expired - please disconnect and reconnect the card reader and then try again",
                                      comment: "Error message when the card reader session has timed out.")
+        case .processorAPIError:
+            return NSLocalizedString("The payment can not be processed by the payment processor.",
+                                     comment: "Error message when the payment can not be processed (i.e. order amount is below the minimum amount allowed.)")
         case .internalServiceError:
             return NSLocalizedString("Sorry, this payment couldn’t be processed",
                                      comment: "Error message when the card reader service experiences an unexpected internal service error.")

Hardware/Hardware/CardReader/StripeCardReader/UnderlyingError+Stripe.swift

@@ -79,6 +79,8 @@ extension UnderlyingError {
             self = .requestTimedOut
         case ErrorCode.Code.sessionExpired.rawValue:
             self = .readerSessionExpired
+        case ErrorCode.Code.stripeAPIError.rawValue:
+            self = .processorAPIError
         default:
             self = .internalServiceError
         }

Hardware/HardwareTests/ErrorCodesTests.swift

@@ -154,6 +154,10 @@ final class CardReaderServiceErrorTests: XCTestCase {
         XCTAssertEqual(.readerSessionExpired, domainError(stripeCode: 9060))
     }
 
+    func test_stripe_error_api_maps_to_stripeAPI() {
+        XCTAssertEqual(.processorAPIError, domainError(stripeCode: 9020))
+    }
+
     func test_stripe_catch_all_error() {
         // Any error code not mapped to an specific error will be
         // mapped to `internalServiceError`

WooCommerce/Classes/ViewModels/CardPresentPayments/PaymentCaptureOrchestrator.swift

@@ -20,6 +20,13 @@ final class PaymentCaptureOrchestrator {
                         onClearMessage: @escaping () -> Void,
                         onProcessingMessage: @escaping () -> Void,
                         onCompletion: @escaping (Result<CardPresentReceiptParameters, Error>) -> Void) {
+        /// Bail out if the order amount is below the minimum allowed:
+        /// https://stripe.com/docs/currencies#minimum-and-maximum-charge-amounts
+        guard isTotalAmountValid(order: order) else {
+            DDLogError("💳 Error: failed to capture payment for order. Order amount is below minimum")
+            onCompletion(.failure(minimumAmountError(order: order, minimumAmount: Constants.minimumAmount)))
+            return
+        }
         /// First ask the backend to create/assign a Stripe customer for the order
         ///
         var customerID: String?
@@ -258,6 +265,30 @@ private extension PaymentCaptureOrchestrator {
     }
 }
 
+private extension PaymentCaptureOrchestrator {
+    enum Constants {
+        /// Minimum order amount in USD:
+        /// https://stripe.com/docs/currencies#minimum-and-maximum-charge-amounts
+        static let minimumAmount = NSDecimalNumber(string: "0.5")
+    }
+
+    func isTotalAmountValid(order: Order) -> Bool {
+        guard let orderTotal = currencyFormatter.convertToDecimal(from: order.total) else {
+            return false
+        }
+
+        return orderTotal as Decimal >= Constants.minimumAmount as Decimal
+    }
+
+    func minimumAmountError(order: Order, minimumAmount: NSDecimalNumber) -> Error {
+        guard let minimum = currencyFormatter.formatAmount(minimumAmount, with: order.currency) else {
+            return NotValidAmountError.other
+        }
+
+        return NotValidAmountError.belowMinimumAmount(amount: minimum)
+    }
+}
+
 private extension PaymentCaptureOrchestrator {
     enum Localization {
         static let receiptDescription = NSLocalizedString("In-Person Payment for Order #%1$@ for %2$@",
@@ -268,3 +299,31 @@ private extension PaymentCaptureOrchestrator {
                                                             + "%2$@ - store name")
     }
 }
+
+private extension PaymentCaptureOrchestrator {
+    private enum NotValidAmountError: Error, LocalizedError {
+        case belowMinimumAmount(amount: String)
+        case other
+
+        public var errorDescription: String? {
+            switch self {
+            case .belowMinimumAmount(let amount):
+                return String.localizedStringWithFormat(Localizations.belowMinimumAmount, amount)
+            case .other:
+                return Localizations.defaultMessage
+            }
+        }
+
+        enum Localizations {
+            static let defaultMessage = NSLocalizedString(
+                "Unable to process payment. Order total amount is not valid.",
+                comment: "Error message when the order amount is not valid."
+            )
+
+            static let belowMinimumAmount = NSLocalizedString(
+                "Unable to process payment. Order total amount is below the minimum amount you can charge, which is %1$@",
+                comment: "Error message when the order amount is below the minimum amount allowed."
+            )
+        }
+    }
+}