[in_app_purchase_storekit] Add support for purchase and transactions flutter#7574 (flutter#7812)

This PR contains the preliminary implementations for handling [purchases](https://developer.apple.com/documentation/storekit/product/3791971-purchase) and [transactions](https://developer.apple.com/documentation/storekit/transaction) 

Of note, as of StoreKit 2, the [result of a call to a purchase will only return a Transaction](https://developer.apple.com/documentation/storekit/product/purchaseresult) when the purchase is successful. If the status of purchase is pending, or cancelled, nothing will be returned. 

This is in contrast to StoreKit 1, where developers could check the state of a Transaction with [TransactionState](https://developer.apple.com/documentation/storekit/skpaymenttransaction/1411275-transactionstate). This means that migrating to StoreKit 2 will require developers to update their handling of transactions accordingly. 

Relands flutter#7574

Author: LouiseHsu

packages/in_app_purchase/in_app_purchase_storekit/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.3.18+2
+
+* Adds support for StoreKit2's `purchase` and `transactions`
+
 ## 0.3.18+1
 
 * Adds support for StoreKit2's `canMakePayments` and `products` 

packages/in_app_purchase/in_app_purchase_storekit/darwin/Classes/InAppPurchasePlugin.swift

@@ -27,6 +27,21 @@ public class InAppPurchasePlugin: NSObject, FlutterPlugin, InAppPurchaseAPI {
   // This property is optional, as it requires self to exist to be initialized.
   public var paymentQueueHandler: FLTPaymentQueueHandlerProtocol?
 
+  // This should be an Task, but Task is on available >= iOS 13
+  private var _updateListenerTask: Any?
+
+  @available(iOS 13.0, *)
+  var updateListenerTask: Task<(), Never> {
+    return self._updateListenerTask as! Task<(), Never>
+  }
+
+  @available(iOS 13.0, *)
+  func setListenerTaskAsTask(task: Task<(), Never>) {
+    self._updateListenerTask = task
+  }
+
+  var transactionCallbackAPI: InAppPurchase2CallbackAPI? = nil
+
   public static func register(with registrar: FlutterPluginRegistrar) {
     #if os(iOS)
       let messenger = registrar.messenger()
@@ -93,6 +108,7 @@ public class InAppPurchasePlugin: NSObject, FlutterPlugin, InAppPurchaseAPI {
       let messenger = registrar.messenger
     #endif
     setupTransactionObserverChannelIfNeeded(withMessenger: messenger)
+    self.transactionCallbackAPI = InAppPurchase2CallbackAPI(binaryMessenger: messenger)
   }
 
   // MARK: - Pigeon Functions

packages/in_app_purchase/in_app_purchase_storekit/darwin/Classes/StoreKit2/InAppPurchaseStoreKit2.swift

@@ -4,16 +4,17 @@
 
 @available(iOS 15.0, macOS 12.0, *)
 extension InAppPurchasePlugin: InAppPurchase2API {
+
   // MARK: - Pigeon Functions
 
-  // Wrapper method around StoreKit2's canMakePayments() method
-  // https://developer.apple.com/documentation/storekit/appstore/3822277-canmakepayments
+  /// Wrapper method around StoreKit2's canMakePayments() method
+  /// https://developer.apple.com/documentation/storekit/appstore/3822277-canmakepayments
   func canMakePayments() throws -> Bool {
     return AppStore.canMakePayments
   }
 
-  // Wrapper method around StoreKit2's products() method
-  // https://developer.apple.com/documentation/storekit/product/3851116-products
+  /// Wrapper method around StoreKit2's products() method
+  /// https://developer.apple.com/documentation/storekit/product/3851116-products
   func products(
     identifiers: [String], completion: @escaping (Result<[SK2ProductMessage], Error>) -> Void
   ) {
@@ -34,4 +35,146 @@ extension InAppPurchasePlugin: InAppPurchase2API {
       }
     }
   }
+
+  /// Gets the appropriate product, then calls purchase on it.
+  /// https://developer.apple.com/documentation/storekit/product/3791971-purchase
+  func purchase(
+    id: String, options: SK2ProductPurchaseOptionsMessage?,
+    completion: @escaping (Result<SK2ProductPurchaseResultMessage, Error>) -> Void
+  ) {
+    Task { @MainActor in
+      do {
+        guard let product = try await Product.products(for: [id]).first else {
+          let error = PigeonError(
+            code: "storekit2_failed_to_fetch_product",
+            message: "Storekit has failed to fetch this product.",
+            details: "Product ID : \(id)")
+          return completion(.failure(error))
+        }
+
+        let result = try await product.purchase(options: [])
+
+        switch result {
+        case .success(let verification):
+          switch verification {
+          case .verified(let transaction):
+            self.sendTransactionUpdate(transaction: transaction)
+            completion(.success(result.convertToPigeon()))
+          case .unverified(_, let error):
+            completion(.failure(error))
+          }
+        case .pending:
+          completion(
+            .failure(
+              PigeonError(
+                code: "storekit2_purchase_pending",
+                message:
+                  "This transaction is still pending and but may complete in the future. If it completes, it will be delivered via `purchaseStream`",
+                details: "Product ID : \(id)")))
+        case .userCancelled:
+          completion(
+            .failure(
+              PigeonError(
+                code: "storekit2_purchase_cancelled",
+                message: "This transaction has been cancelled by the user.",
+                details: "Product ID : \(id)")))
+        @unknown default:
+          fatalError("An unknown StoreKit PurchaseResult has been encountered.")
+        }
+      } catch {
+        completion(.failure(error))
+      }
+    }
+  }
+
+  /// Wrapper method around StoreKit2's transactions() method
+  /// https://developer.apple.com/documentation/storekit/product/3851116-products
+  func transactions(
+    completion: @escaping (Result<[SK2TransactionMessage], Error>) -> Void
+  ) {
+    Task {
+      @MainActor in
+      do {
+        let transactionsMsgs = await rawTransactions().map {
+          $0.convertToPigeon()
+        }
+        completion(.success(transactionsMsgs))
+      }
+    }
+  }
+
+  /// Wrapper method around StoreKit2's finish() method https://developer.apple.com/documentation/storekit/transaction/3749694-finish
+  func finish(id: Int64, completion: @escaping (Result<Void, Error>) -> Void) {
+    Task {
+      let transaction = try await fetchTransaction(by: UInt64(id))
+      if let transaction = transaction {
+        await transaction.finish()
+      }
+    }
+  }
+
+  /// This Task listens  to Transation.updates as shown here
+  /// https://developer.apple.com/documentation/storekit/transaction/3851206-updates
+  /// This function should be called as soon as the app starts to avoid missing any Transactions done outside of the app.
+  func startListeningToTransactions() throws {
+    self.setListenerTaskAsTask(
+      task: Task { [weak self] in
+        for await verificationResult in Transaction.updates {
+          switch verificationResult {
+          case .verified(let transaction):
+            self?.sendTransactionUpdate(transaction: transaction)
+          case .unverified:
+            break
+          }
+        }
+      })
+  }
+
+  /// Stop subscribing to Transaction.updates
+  func stopListeningToTransactions() throws {
+    updateListenerTask.cancel()
+  }
+
+  /// Sends an transaction back to Dart. Access these transactions with `purchaseStream`
+  func sendTransactionUpdate(transaction: Transaction) {
+    let transactionMessage = transaction.convertToPigeon()
+    transactionCallbackAPI?.onTransactionsUpdated(newTransaction: transactionMessage) { result in
+      switch result {
+      case .success: break
+      case .failure(let error):
+        print("Failed to send transaction updates: \(error)")
+      }
+    }
+  }
+
+  // MARK: - Convenience Functions
+
+  /// Helper function that fetches and unwraps all verified transactions
+  private func rawTransactions() async -> [Transaction] {
+    var transactions: [Transaction] = []
+    for await verificationResult in Transaction.all {
+      switch verificationResult {
+      case .verified(let transaction):
+        transactions.append(transaction)
+      case .unverified:
+        break
+      }
+    }
+    return transactions
+  }
+
+  /// Helper function to fetch specific transaction
+  private func fetchTransaction(by id: UInt64) async throws -> Transaction? {
+    for await result in Transaction.all {
+      switch result {
+      case .verified(let transaction):
+        if transaction.id == id {
+          return transaction
+        }
+      case .unverified:
+        continue
+      }
+    }
+    return nil
+  }
 }

packages/in_app_purchase/in_app_purchase_storekit/darwin/Classes/StoreKit2/StoreKit2Translators.swift

@@ -167,3 +167,38 @@ extension SK2PriceLocaleMessage: Equatable {
     return lhs.currencyCode == rhs.currencyCode && lhs.currencySymbol == rhs.currencySymbol
   }
 }
+
+@available(iOS 15.0, macOS 12.0, *)
+extension Product.PurchaseResult {
+  func convertToPigeon() -> SK2ProductPurchaseResultMessage {
+    switch self {
+    case .success(_):
+      return SK2ProductPurchaseResultMessage.success
+    case .userCancelled:
+      return SK2ProductPurchaseResultMessage.userCancelled
+    case .pending:
+      return SK2ProductPurchaseResultMessage.pending
+    @unknown default:
+      fatalError()
+    }
+  }
+}
+
+@available(iOS 15.0, macOS 12.0, *)
+extension Transaction {
+  func convertToPigeon(restoring: Bool = false) -> SK2TransactionMessage {
+
+    let dateFromatter: DateFormatter = DateFormatter()
+    dateFromatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
+
+    return SK2TransactionMessage(
+      id: Int64(id),
+      originalId: Int64(originalID),
+      productId: productID,
+      purchaseDate: dateFromatter.string(from: purchaseDate),
+      purchasedQuantity: Int64(purchasedQuantity),
+      appAccountToken: appAccountToken?.uuidString,
+      restoring: restoring
+    )
+  }
+}