Strategy Pattern

strategyPattern.swift

import UIKit
import Combine

// MADE UP CODE
typealias Package = Int

struct Offerings {
	var monthtly: Package?
	var annual: Package?
	var lifetime: Package?
}

protocol PurchaseStrategy {
	init(package: Package?)
	func purchase(completion: @escaping (Bool) -> Void)
}

struct MonthlyPurchaseStrategy: PurchaseStrategy {
	init(package: Package?) {}
	func purchase(completion: @escaping (Bool) -> Void) {
		print(#function, "Monthly")
		completion(true)
	}
}

struct AnnualPurchaseStrategy: PurchaseStrategy {
	init(package: Package?) {}
	func purchase(completion: @escaping (Bool) -> Void) {
		print(#function, "Annual")
		completion(true)
	}
}

struct LifetimePurchaseStrategy: PurchaseStrategy {
	init(package: Package?) {}
	func purchase(completion: @escaping (Bool) -> Void) {
		print(#function, "Lifetime")
		completion(true)
	}
}

struct EmptyPackagePurchaseStrategy: PurchaseStrategy {
	init(package: Package?) {}
	func purchase(completion: @escaping (Bool) -> Void) {
		print(#function, "Sad Panda")
		completion(false)
	}
}

enum PurchaseStrategyFactory {
	static func makePackage(offerings: Offerings?) -> PurchaseStrategy {
		guard let offerings = offerings else {
			return EmptyPackagePurchaseStrategy(package: nil)
		}
		if let monthly = offerings.monthtly {
			return MonthlyPurchaseStrategy(package: monthly)
		} else if let annual = offerings.annual {
			return AnnualPurchaseStrategy(package: annual)
		} else if let lifetime = offerings.lifetime {
			return LifetimePurchaseStrategy(package: lifetime)
		} else {
			return EmptyPackagePurchaseStrategy(package: nil)
		}
	}
}

class PaywallViewModel: ObservableObject {
	var offerings: Offerings?

	init(offerings: Offerings?) {
		self.offerings = offerings
	}

	func handleSubscribeButton() {
		let purchaseStrategy = PurchaseStrategyFactory.makePackage(
			offerings: offerings
		)
		purchaseStrategy.purchase { [weak self] completed in
			print(completed)
		}
	}
}

// Strategy can be swapped if needed
// Also makes it easier to unit test your strategies.
// This can be also improved by injecting factory etc.
let paywall = PaywallViewModel(offerings: Offerings(monthtly: 20))
paywall.handleSubscribeButton()

paywall.offerings = Offerings(annual: 20)
paywall.handleSubscribeButton()

paywall.offerings = Offerings(lifetime: 20)
paywall.handleSubscribeButton()

paywall.offerings = nil
paywall.handleSubscribeButton()