Add StoreProduct.pricePerYear

Sources/Purchasing/StoreKitAbstractions/StoreProduct.swift

@@ -132,6 +132,7 @@ internal protocol StoreProductType: Sendable {
     ///
     /// #### Related Symbols
     /// - ``pricePerMonth``
+    /// - ``pricePerYear``
     var price: Decimal { get }
 
     /// The price of this product using ``priceFormatter``.
@@ -202,6 +203,7 @@ public extension StoreProduct {
     ///
     /// #### Related Symbols
     /// - ``pricePerMonth``
+    /// - ``pricePerYear``
     @objc(price) var priceDecimalNumber: NSDecimalNumber {
         return self.price as NSDecimalNumber
     }
@@ -213,6 +215,13 @@ public extension StoreProduct {
         return self.subscriptionPeriod?.pricePerMonth(withTotalPrice: self.price) as NSDecimalNumber?
     }
 
+    /// Calculates the price of this subscription product per year.
+    /// - Returns: `nil` if the product is not a subscription.
+    @available(iOS 11.2, macOS 10.13.2, tvOS 11.2, watchOS 6.2, *)
+    @objc var pricePerYear: NSDecimalNumber? {
+        return self.subscriptionPeriod?.pricePerYear(withTotalPrice: self.price) as NSDecimalNumber?
+    }
+
     /// The price of the `introductoryPrice` formatted using ``priceFormatter``.
     /// - Returns: `nil` if there is no `introductoryPrice`.
     @objc var localizedIntroductoryPriceString: String? {

Sources/Purchasing/StoreKitAbstractions/SubscriptionPeriod.swift

@@ -102,18 +102,38 @@ extension SubscriptionPeriod.Unit: Sendable {}
 extension SubscriptionPeriod: Sendable {}
 
 extension SubscriptionPeriod {
+
     func pricePerMonth(withTotalPrice price: Decimal) -> Decimal {
-        let periodsPerMonth: Decimal = {
-            switch self.unit {
-            case .day: return 1 / 30
-            case .week: return 1 / 4
-            case .month: return 1
-            case .year: return 12
-            }
-        }() * Decimal(self.value)
-
-        return (price as NSDecimalNumber)
-            .dividing(by: periodsPerMonth as NSDecimalNumber,
+        return self.pricePerPeriod(for: self.unitsPerMonth, totalPrice: price)
+    }
+
+    func pricePerYear(withTotalPrice price: Decimal) -> Decimal {
+        return self.pricePerPeriod(for: self.unitsPerYear, totalPrice: price)
+    }
+
+    private var unitsPerMonth: Decimal {
+        switch self.unit {
+        case .day: return 1 / 30
+        case .week: return 1 / 4
+        case .month: return 1
+        case .year: return 12
+        }
+    }
+
+    private var unitsPerYear: Decimal {
+        switch self.unit {
+        case .day: return 1 / 365
+        case .week: return 1 / 52.14 // Number of weeks in a year
+        case .month: return 1 / 12
+        case .year: return 1
+        }
+    }
+
+    private func pricePerPeriod(for units: Decimal, totalPrice: Decimal) -> Decimal {
+        let periods: Decimal = units * Decimal(self.value)
+
+        return (totalPrice as NSDecimalNumber)
+            .dividing(by: periods as NSDecimalNumber,
                       withBehavior: Self.roundingBehavior) as Decimal
     }
 
@@ -125,6 +145,7 @@ extension SubscriptionPeriod {
         raiseOnUnderflow: false,
         raiseOnDivideByZero: false
     )
+
 }
 
 extension SubscriptionPeriod.Unit: CustomDebugStringConvertible {

Tests/APITesters/ObjCAPITester/ObjCAPITester/RCStoreProductAPI.m

@@ -27,6 +27,7 @@ + (void)checkAPI {
     RCStoreProductDiscount *introductoryPrice = product.introductoryDiscount;
     NSArray<RCStoreProductDiscount *> *discounts = product.discounts;
     NSDecimalNumber *pricePerMonth = product.pricePerMonth;
+    NSDecimalNumber *pricePerYear = product.pricePerYear;
     NSString *localizedIntroductoryPriceString = product.localizedIntroductoryPriceString;
 
     SKProduct *sk1 = product.sk1Product;
@@ -46,6 +47,7 @@ + (void)checkAPI {
           introductoryPrice,
           discounts,
           pricePerMonth,
+          pricePerYear,
           localizedIntroductoryPriceString,
           sk1
       );

Tests/APITesters/SwiftAPITester/SwiftAPITester/StoreProductAPI.swift

@@ -28,6 +28,7 @@ func checkStoreProductAPI() {
     let discounts: [StoreProductDiscount] = product.discounts
 
     let pricePerMonth: NSDecimalNumber? = product.pricePerMonth
+    let pricePerYear: NSDecimalNumber? = product.pricePerYear
     let localizedIntroductoryPriceString: String? = product.localizedIntroductoryPriceString
     let sk1Product: SK1Product? = product.sk1Product
     let sk2Product: SK2Product? = product.sk2Product
@@ -56,6 +57,7 @@ func checkStoreProductAPI() {
         introductoryPrice!,
         discounts,
         pricePerMonth!,
+        pricePerYear!,
         localizedIntroductoryPriceString!,
         sk1Product!,
         sk2Product!

Tests/UnitTests/Purchasing/StoreKitAbstractions/SubscriptionPeriodTests.swift

@@ -70,6 +70,33 @@ class SubscriptionPeriodTests: TestCase {
         }
     }
 
+    func testPricePerYear() {
+        let expectations: [(period: SubscriptionPeriod, price: Decimal, expected: Decimal)] = [
+            (p(1, .day), 1, 365),
+            (p(1, .day), 2, 730),
+            (p(15, .day), 5, 121.66),
+            (p(1, .week), 10, 521.4),
+            (p(2, .week), 10, 260.7),
+            (p(1, .month), 14.99, 179.88),
+            (p(1, .month), 5, 60),
+            (p(2, .month), 30, 180),
+            (p(3, .month), 40, 160),
+            (p(1, .year), 120, 120),
+            (p(1, .year), 29.99, 29.99),
+            (p(2, .year), 50, 25),
+            (p(3, .year), 720, 240)
+        ]
+
+        for expectation in expectations {
+            let pricePerYear = expectation.period.pricePerYear(withTotalPrice: expectation.price) as NSDecimalNumber
+            let result = Double(truncating: pricePerYear)
+            let expected = Double(truncating: expectation.expected as NSDecimalNumber)
+
+            expect(result).to(beCloseTo(expected),
+                              description: "\(expectation.price) / \(expectation.period.debugDescription)")
+        }
+    }
+
     private func p(_ value: Int, _ unit: SubscriptionPeriod.Unit) -> SubscriptionPeriod {
         return .init(value: value, unit: unit)
     }