iap: move StoreKit logic out of DamusPurpleView and into a new PurpleStoreKitManager

This commit moves most of StoreKit-specific logic that was embedded into
DamusPurpleView and places it into a new PurpleStoreKitManager struct,
to make code more reusable and readable by separating view concerns from
StoreKit-specific concerns.

Most of the code here should be in feature parity with the previous
behavior. However, a few logical improvements were made alongside this
refactoring:

- Improved StoreKit transaction update monitoring logic: Previously the
  view would stop listening for purchase updates after the first update.
  However, I made the program continuously listen for purchase updates,
  as recommended by Apple's documentation
  (https://developer.apple.com/documentation/storekit/transaction/3851206-updates)

- Improved/simplified logic around getting extra information from the
  products: Information and the handling of product information was
  spread in a few separate places. I incorporated those bits of
  information into central and uniform interfaces on DamusPurpleType, to
  simplify logic and future changes.

Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
Reviewed-by: William Casarin <jb55@jb55.com>
Signed-off-by: William Casarin <jb55@jb55.com>

damus/Views/Purple/DamusPurpleView.swift

@@ -8,8 +8,6 @@
 import SwiftUI
 import StoreKit
 
-fileprivate let damus_products = ["purpleyearly","purple"]
-
 // MARK: - Helper structures
 
 enum AccountInfoState {
@@ -19,25 +17,16 @@ enum AccountInfoState {
     case error(message: String)
 }
 
-func non_discounted_price(_ product: Product) -> String {
-    return (product.price * 1.1984569224).formatted(product.priceFormatStyle)
-}
-
-enum DamusPurpleType: String {
-    case yearly = "purpleyearly"
-    case monthly = "purple"
-}
-
 // MARK: - Main view
 
-struct DamusPurpleView: View {
+struct DamusPurpleView: View, DamusPurpleStoreKitManagerDelegate {
     let damus_state: DamusState
     let keypair: Keypair
     
     @State var my_account_info_state: AccountInfoState = .loading
     @State var products: ProductState
     @State var purchased: PurchasedProduct? = nil
-    @State var selection: DamusPurpleType = .yearly
+    @State var selection: DamusPurple.StoreKitManager.DamusPurpleType = .yearly
     @State var show_welcome_sheet: Bool = false
     @State var show_manage_subscriptions = false
     @State private var shouldDismissView = false
@@ -48,6 +37,7 @@ struct DamusPurpleView: View {
         self._products = State(wrappedValue: .loading)
         self.damus_state = damus_state
         self.keypair = damus_state.keypair
+        damus_state.purple.storekit_manager.delegate = self
     }
     
     // MARK: - Top level view
@@ -159,30 +149,10 @@ struct DamusPurpleView: View {
         }
     }
     
-    func handle_transactions(products: [Product]) async {
-        for await update in StoreKit.Transaction.updates {
-            switch update {
-                case .verified(let tx):
-                    let prod = products.filter({ prod in tx.productID == prod.id }).first
-                    
-                    if let prod,
-                       let expiration = tx.expirationDate,
-                       Date.now < expiration
-                    {
-                        self.purchased = PurchasedProduct(tx: tx, product: prod)
-                        break
-                    }
-                case .unverified:
-                    continue
-            }
-        }
-    }
-    
     func load_products() async {
         do {
-            let products = try await Product.products(for: damus_products)
+            let products = try await self.damus_state.purple.storekit_manager.get_products()
             self.products = .loaded(products)
-            await handle_transactions(products: products)
 
             print("loaded products", products)
         } catch {
@@ -191,8 +161,13 @@ struct DamusPurpleView: View {
         }
     }
     
+    // For DamusPurple.StoreKitManager.Delegate conformance. This gets called by the StoreKitManager when a new product was purchased
+    func product_was_purchased(product: DamusPurple.StoreKitManager.PurchasedProduct) {
+        self.purchased = product
+    }
+    
     func subscribe(_ product: Product) async throws {
-        let result = try await product.purchase()
+        let result = try await self.damus_state.purple.make_iap_purchase(product: product)
         switch result {
             case .success(.verified(let tx)):
                 print("success \(tx.debugDescription)")
@@ -219,12 +194,6 @@ struct DamusPurpleView: View {
                 break
         }
     }
-    
-    var product: Product? {
-        return self.products.products?.filter({
-            prod in prod.id == selection.rawValue
-        }).first
-    }
 }
 
 struct DamusPurpleView_Previews: PreviewProvider {

damus/Views/Purple/Detail/IAPProductStateView.swift

@@ -11,6 +11,8 @@ import StoreKit
 // MARK: - IAPProductStateView
 
 extension DamusPurpleView {
+    typealias PurchasedProduct = DamusPurple.StoreKitManager.PurchasedProduct
+    
     struct IAPProductStateView: View {
         let products: ProductState
         let purchased: PurchasedProduct?
@@ -82,28 +84,20 @@ extension DamusPurpleView {
         }
         
         func price_description(product: Product) -> some View {
-            if product.id == "purpleyearly" {
-                return (
-                    AnyView(
-                        HStack(spacing: 10) {
-                            Text(NSLocalizedString("Annually", comment: "Annual renewal of purple subscription"))
-                            Spacer()
-                            Text(verbatim: non_discounted_price(product)).strikethrough().foregroundColor(DamusColors.white.opacity(0.5))
-                            Text(verbatim: product.displayPrice).fontWeight(.bold)
-                        }
-                    )
-                )
-            } else {
-                return (
-                    AnyView(
-                        HStack(spacing: 10) {
-                            Text(NSLocalizedString("Monthly", comment: "Monthly renewal of purple subscription"))
-                            Spacer()
-                            Text(verbatim: product.displayPrice).fontWeight(.bold)
-                        }
-                    )
-                )
-            }
+            let purple_type = DamusPurple.StoreKitManager.DamusPurpleType(rawValue: product.id)
+            return (
+                HStack(spacing: 10) {
+                    Text(purple_type?.label() ?? product.displayName)
+                    Spacer()
+                    if let non_discounted_price = purple_type?.non_discounted_price(product: product) {
+                        Text(verbatim: non_discounted_price)
+                            .strikethrough()
+                            .foregroundColor(DamusColors.white.opacity(0.5))
+                    }
+                    Text(verbatim: product.displayPrice)
+                        .fontWeight(.bold)
+                }
+            )
         }
     }
 }
@@ -127,11 +121,6 @@ extension DamusPurpleView {
             }
         }
     }
-    
-    struct PurchasedProduct {
-        let tx: StoreKit.Transaction
-        let product: Product
-    }
 }
 
 #Preview {