Paywalls: determine intro eligibility (#2808)

Follow up to #2796.
This also makes `PaywallData.Configuration`'s intro strings optional.

- Injected `TrialOrIntroEligibilityChecker`
- Created mock `TrialOrIntroEligibilityChecker` for previews
- Handling state and transitions for loading eligibility
- Snapshot tests for the different new cases
- Improved `SnapshotTesting` delay management
- Expanded `DebugErrorView` to customize release behavior

RevenueCatUI/Helpers/Constants.swift

@@ -0,0 +1,15 @@
+//
+//  Constants.swift
+//  
+//
+//  Created by Nacho Soto on 7/13/23.
+//
+
+import SwiftUI
+
+@available(iOS 16.0, macOS 13.0, tvOS 16.0, *)
+enum Constants {
+
+    static let defaultAnimation: Animation = .easeIn(duration: 0.2)
+
+}

RevenueCatUI/Helpers/DebugErrorView.swift

@@ -13,13 +13,25 @@ import SwiftUI
 struct DebugErrorView: View {
 
     private let description: String
+    private let releaseBehavior: ReleaseBehavior
+
+    enum ReleaseBehavior {
+
+        case emptyView
+        case fatalError
 
-    init(_ error: Error) {
-        self.init((error as NSError).localizedDescription)
     }
 
-    init(_ description: String) {
+    init(_ error: Error, releaseBehavior: ReleaseBehavior) {
+        self.init(
+            (error as NSError).localizedDescription,
+            releaseBehavior: releaseBehavior
+        )
+    }
+
+    init(_ description: String, releaseBehavior: ReleaseBehavior) {
         self.description = description
+        self.releaseBehavior = releaseBehavior
     }
 
     var body: some View {
@@ -30,12 +42,16 @@ struct DebugErrorView: View {
                     .edgesIgnoringSafeArea(.all)
             )
         #else
-        // Fix-me: implement a proper production error screen
-        // appropriate for each case
-        EmptyView()
-            .onAppear {
-                Logger.warning("Couldn't load paywall: \(self.description)")
-            }
+        switch self.releaseBehavior {
+        case .emptyView:
+            EmptyView()
+                .onAppear {
+                    Logger.warning("Couldn't load paywall: \(self.description)")
+                }
+
+        case let .fatalError:
+            fatalError(self.description)
+        }
         #endif
     }
 

RevenueCatUI/Helpers/ProcessedLocalizedConfiguration.swift

@@ -6,9 +6,9 @@ struct ProcessedLocalizedConfiguration: PaywallLocalizedConfiguration {
     var title: String
     var subtitle: String
     var callToAction: String
-    var callToActionWithIntroOffer: String
+    var callToActionWithIntroOffer: String?
     var offerDetails: String
-    var offerDetailsWithIntroOffer: String
+    var offerDetailsWithIntroOffer: String?
 
     init(
         _ configuration: PaywallData.LocalizedConfiguration,
@@ -18,19 +18,19 @@ struct ProcessedLocalizedConfiguration: PaywallLocalizedConfiguration {
             title: configuration.title.processed(with: dataProvider),
             subtitle: configuration.subtitle.processed(with: dataProvider),
             callToAction: configuration.callToAction.processed(with: dataProvider),
-            callToActionWithIntroOffer: configuration.callToActionWithIntroOffer.processed(with: dataProvider),
+            callToActionWithIntroOffer: configuration.callToActionWithIntroOffer?.processed(with: dataProvider),
             offerDetails: configuration.offerDetails.processed(with: dataProvider),
-            offerDetailsWithIntroOffer: configuration.offerDetailsWithIntroOffer.processed(with: dataProvider)
+            offerDetailsWithIntroOffer: configuration.offerDetailsWithIntroOffer?.processed(with: dataProvider)
         )
     }
 
     private init(
         title: String,
         subtitle: String,
         callToAction: String,
-        callToActionWithIntroOffer: String,
+        callToActionWithIntroOffer: String?,
         offerDetails: String,
-        offerDetailsWithIntroOffer: String
+        offerDetailsWithIntroOffer: String?
     ) {
         self.title = title
         self.subtitle = subtitle

RevenueCatUI/Helpers/TrialOrIntroEligibilityChecker.swift

@@ -0,0 +1,56 @@
+//
+//  TrialOrIntroEligibilityChecker.swift
+//  
+//
+//  Created by Nacho Soto on 7/13/23.
+//
+
+import Foundation
+import RevenueCat
+
+@available(iOS 13.0, tvOS 13.0, macOS 10.15, watchOS 6.2, *)
+final class TrialOrIntroEligibilityChecker: ObservableObject {
+
+    typealias Checker = @Sendable (StoreProduct) async -> IntroEligibilityStatus
+
+    let checker: Checker
+
+    convenience init(purchases: Purchases = .shared) {
+        self.init { product in
+            guard product.hasIntroDiscount else {
+                return .noIntroOfferExists
+            }
+
+            return await purchases.checkTrialOrIntroDiscountEligibility(product: product)
+        }
+    }
+
+    /// Creates an instance with a custom checker, useful for testing or previews.
+    init(checker: @escaping Checker) {
+        self.checker = checker
+    }
+
+}
+
+@available(iOS 13.0, tvOS 13.0, macOS 10.15, watchOS 6.2, *)
+extension TrialOrIntroEligibilityChecker {
+
+    func eligibility(for product: StoreProduct) async -> IntroEligibilityStatus {
+        return await self.checker(product)
+    }
+
+    func eligibility(for package: Package) async -> IntroEligibilityStatus {
+        return await self.eligibility(for: package.storeProduct)
+    }
+
+}
+
+@available(iOS 13.0, tvOS 13.0, macOS 10.15, watchOS 6.2, *)
+extension StoreProduct {
+
+    var hasIntroDiscount: Bool {
+        // Fix-me: this needs to handle other types of intro discounts
+        return self.introductoryDiscount != nil
+    }
+
+}

RevenueCatUI/Modifiers/ViewExtensions.swift

@@ -0,0 +1,23 @@
+//
+//  ViewExtensions.swift
+//  
+//
+//  Created by Nacho Soto on 7/13/23.
+//
+
+import Foundation
+import SwiftUI
+
+@available(iOS 13.0, tvOS 13.0, macOS 10.15, watchOS 6.2, *)
+extension View {
+
+    @ViewBuilder
+    func hidden(if condition: Bool) -> some View {
+        if condition {
+            self.hidden()
+        } else {
+            self
+        }
+    }
+
+}

RevenueCatUI/PaywallView.swift

@@ -1,21 +1,40 @@
 import RevenueCat
 import SwiftUI
 
-// swiftlint:disable missing_docs
-
+/// A full-screen SwiftUI view for displaying a `PaywallData` for an `Offering`.
 @available(iOS 16.0, macOS 13.0, tvOS 16.0, *)
 public struct PaywallView: View {
 
     private let offering: Offering
     private let paywall: PaywallData
+    private let introEligibility: TrialOrIntroEligibilityChecker?
 
+    /// Create a view for the given offering and paywal.
+    /// - Warning: `Purchases` must have been configured prior to displaying it.
     public init(offering: Offering, paywall: PaywallData) {
+        self.init(
+            offering: offering,
+            paywall: paywall,
+            introEligibility: Purchases.isConfigured ? .init() : nil
+        )
+    }
+
+    init(offering: Offering, paywall: PaywallData, introEligibility: TrialOrIntroEligibilityChecker?) {
         self.offering = offering
         self.paywall = paywall
+        self.introEligibility = introEligibility
     }
 
+    // swiftlint:disable:next missing_docs
     public var body: some View {
-        self.paywall.createView(for: self.offering)
+        if let checker = self.introEligibility {
+            self.paywall
+                .createView(for: self.offering)
+                .environmentObject(checker)
+        } else {
+            DebugErrorView("Purchases has not been configured.",
+                           releaseBehavior: .fatalError)
+        }
     }
 
 }
@@ -26,8 +45,19 @@ public struct PaywallView: View {
 struct PaywallView_Previews: PreviewProvider {
 
     static var previews: some View {
-        let offering = TestData.offeringWithIntroOffer
-        PaywallView(offering: offering, paywall: offering.paywall!)
+        let offering = TestData.offeringWithNoIntroOffer
+
+        if let paywall = offering.paywall {
+            PaywallView(
+                offering: offering,
+                paywall: paywall,
+                introEligibility: TrialOrIntroEligibilityChecker
+                    .producing(eligibility: .eligible)
+                    .with(delay: .seconds(1))
+            )
+        } else {
+            Text("Preview not correctly setup, offering has no paywall!")
+        }
     }
 
 }