Sample implementation of In-App purchase manager class

InAppPurchaseManager.swift

// MIT License
// 
// Copyright (c) 2019 Rostyslav Dovhaliuk
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

import RxSwift
import RxCocoa
import StoreKit
import Kvitto
import Crashlytics

enum RestorePurchaseStatus {
    case loading
    case finished
    case failed(error: Error)
}

enum ProductsStatus {
    case pending
    case loading
    case loaded(subscription: SKProduct, proVersion: SKProduct)
    case failed(error: Error)
}

enum TransactionStatus {
    case pending
    case purchasing
    case purchased
    case failed(error: Error?)
    case deferred
}

enum PurchaseStatus {
    case noPurchases
    case purchasedProVersion
    case activeSubscription(expDate: Date)
    case expiredSubscription(expDate: Date)
    case purchasedProVersionAndSubscription(expDate: Date)
    
    var givesAccessToProTools: Bool {
        switch self {
        case .purchasedProVersion, .activeSubscription, .purchasedProVersionAndSubscription: return true
        default: return false
        }
    }
    
    var proVersionPurchased: Bool {
        switch self {
        case .purchasedProVersion, .purchasedProVersionAndSubscription: return true
        default: return false
        }
    }
}

enum PurchaseError: LocalizedError {
    case noMatchingProductFound
    
    var errorDescription: String? {
        switch self {
        case .noMatchingProductFound:
            return "Can't find SKProduct with matching identifier"
        }
    }
}

private enum InAppID: String, CaseIterable {
    case subscription = "com.eehelper.pro_subscription"
    case proVersion = "com.eehelper.pro_version"
}

private let inAppPurchasesIdentifiers = Set(InAppID.allCases.map { $0.rawValue })

class InAppPurchaseManager: NSObject {
    static let shared = InAppPurchaseManager()
    
    let inAppPurchaseStatus: BehaviorRelay<PurchaseStatus> = BehaviorRelay(value: .noPurchases)
    let purchaseRestorationEvents: PublishRelay<RestorePurchaseStatus> = PublishRelay()
    let productsEvents: BehaviorRelay<ProductsStatus> = BehaviorRelay(value: .pending)
    let transactionEvents: BehaviorRelay<TransactionStatus> = BehaviorRelay(value: .pending)
    
    func loadProducts() {
        productsEvents.accept(.loading)
        
        let request = SKProductsRequest(productIdentifiers: inAppPurchasesIdentifiers)
        request.delegate = self
        request.start()
    }
    
    func purchase(_ product: SKProduct) {
        let payment = SKPayment(product: product)
        SKPaymentQueue.default().add(payment)
    }
    
    func restorePurchase() {
        purchaseRestorationEvents.accept(.loading)
        SKPaymentQueue.default().restoreCompletedTransactions()
    }
    
    // MARK: - Private
    private override init() {
        super.init()
        inAppPurchaseStatus.accept(readReceipt())
        SKPaymentQueue.default().add(self)
    }
    
    private func readReceipt() -> PurchaseStatus {
        guard let url = Bundle.main.appStoreReceiptURL,
              let receipt = Receipt(contentsOfURL: url)
        else {
            return .noPurchases
        }
        
        let proVersionReceipt = receipt.inAppPurchaseReceipts?
            .filter({ $0.productIdentifier == InAppID.proVersion.rawValue })
            .first
        
        let subscriptionLatestExpDate = receipt.inAppPurchaseReceipts?
            .filter({ $0.productIdentifier == InAppID.subscription.rawValue })
            .compactMap({ $0.subscriptionExpirationDate })
            .sorted(by: { $0 > $1 })
            .first
        
        switch (proVersionReceipt, subscriptionLatestExpDate) {
        case (nil, nil): return .noPurchases
        case (.some, nil): return .purchasedProVersion
        case (nil, .some(let date)):
            return date > Date() ? .activeSubscription(expDate: date) : .expiredSubscription(expDate: date)
        case (.some, .some(let date)):
            return date > Date() ? .purchasedProVersionAndSubscription(expDate: date) : .purchasedProVersion
        }
    }
}

extension InAppPurchaseManager: SKProductsRequestDelegate {
    func productsRequest(_ request: SKProductsRequest, didReceive response: SKProductsResponse) {
        let products = response.products
        guard
            let subscription = products.first(where: { $0.productIdentifier == InAppID.subscription.rawValue }),
            let nonconsumable = products.first(where: { $0.productIdentifier == InAppID.proVersion.rawValue })
        else {
            Crashlytics.sharedInstance().recordError(PurchaseError.noMatchingProductFound)
            productsEvents.accept(.failed(error: PurchaseError.noMatchingProductFound))
            return
        }
        productsEvents.accept(.loaded(subscription: subscription, proVersion: nonconsumable))
    }
    
    func request(_ request: SKRequest, didFailWithError error: Error) {
        productsEvents.accept(.failed(error: error))
    }
    
    func paymentQueue(_ queue: SKPaymentQueue, updatedTransactions transactions: [SKPaymentTransaction]) {
        for transaction in transactions where inAppPurchasesIdentifiers.contains(transaction.payment.productIdentifier) {
            switch transaction.transactionState {
            case .purchasing:
                transactionEvents.accept(.purchasing)
            case .purchased, .restored:
                transactionEvents.accept(.purchased)
                queue.finishTransaction(transaction)
            case .failed:
                transactionEvents.accept(.failed(error: transaction.error))
                queue.finishTransaction(transaction)
            case .deferred:
                transactionEvents.accept(.deferred)
            }
        }
        inAppPurchaseStatus.accept(readReceipt())
    }
}

extension InAppPurchaseManager: SKPaymentTransactionObserver {
    func paymentQueueRestoreCompletedTransactionsFinished(_ queue: SKPaymentQueue) {
        purchaseRestorationEvents.accept(.finished)
    }
    
    func paymentQueue(_ queue: SKPaymentQueue, restoreCompletedTransactionsFailedWithError error: Error) {
        purchaseRestorationEvents.accept(.failed(error: error))
    }
    
    @available(iOS 14.0, *)
    func paymentQueue(_ queue: SKPaymentQueue, didRevokeEntitlementsForProductIdentifiers productIdentifiers: [String]) {
        inAppPurchaseStatusRelay.accept(readReceipt())
    }
}

This is great. I would like to implement in my app. but don't know what is "Receipt".
I know that is out of scope. but if you can provide class or structure of "Receipt" then it would be awesome.

@mrugeshtank You can find more information about receipt structure at
https://developer.apple.com/library/archive/releasenotes/General/ValidateAppStoreReceipt/Chapters/ReceiptFields.html
https://www.revenuecat.com/blog/dissecting-an-app-store-receipt
Or simply use Kvitto library, which hides all this complexity.