Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Extensions/StoreKit/Sources/SKPaymentQueue+Promise.swift

@@ -0,0 +1,55 @@
+#if !PMKCocoaPods
+import PromiseKit
+#endif
+import StoreKit
+
+public extension SKPaymentQueue {
+    func restoreCompletedTransactions(_: PMKNamespacer) -> Promise<[SKPaymentTransaction]> {
+        return PaymentObserver(self).promise
+    }
+
+    func restoreCompletedTransactions(_: PMKNamespacer, withApplicationUsername username: String?) -> Promise<[SKPaymentTransaction]> {
+        return PaymentObserver(self, withApplicationUsername: true, userName: username).promise
+    }
+}
+
+private class PaymentObserver: NSObject, SKPaymentTransactionObserver {
+    let (promise, seal) = Promise<[SKPaymentTransaction]>.pending()
+    var retainCycle: PaymentObserver?
+    var finishedTransactions = [SKPaymentTransaction]()
+
+    //TODO:PMK7: this is weird, just have a `String?` parameter
+    init(_ paymentQueue: SKPaymentQueue, withApplicationUsername: Bool = false, userName: String? = nil) {
+        super.init()
+        paymentQueue.add(self)
+        withApplicationUsername ?
+            paymentQueue.restoreCompletedTransactions() :
+            paymentQueue.restoreCompletedTransactions(withApplicationUsername: userName)
+        retainCycle = self
+    }
+
+    func paymentQueue(_ queue: SKPaymentQueue, updatedTransactions transactions: [SKPaymentTransaction]) {
+        for transaction in transactions where transaction.transactionState == .restored {
+            finishedTransactions.append(transaction)
+            queue.finishTransaction(transaction)
+        }
+    }
+
+    func paymentQueueRestoreCompletedTransactionsFinished(_ queue: SKPaymentQueue) {
+        resolve(queue, nil)
+    }
+
+    func paymentQueue(_ queue: SKPaymentQueue, restoreCompletedTransactionsFailedWithError error: Error) {
+        resolve(queue, error)
+    }
+
+    func resolve(_ queue: SKPaymentQueue, _ error: Error?) {
+        if let error = error {
+            seal.reject(error)
+        } else {
+            seal.fulfill(finishedTransactions)
+        }
+        queue.remove(self)
+        retainCycle = nil
+    }
+}