Payments Module

protocol PaymentsClient: Sendable {
    func configure(_ config: PaymentsConfig) async
    func purchase(productID: String) async throws
    func restorePurchases() async throws
    func currentState() async -> PaymentsState
    func subscriptionStates() -> AsyncStream<PaymentsState>
}

struct PaymentsState: Sendable {
    let isSubscribed: Bool
    let expirationDate: Date?
    let activeEntitlementIDs: Set<String>
    let willRenew: Bool
}

// 1. Create RevenueCat client
let revenueCatClient = Payments.RevenueCatClient()

// 2. Configuration happens at app launch via AppDelegate
// Config comes from Secrets.xcconfig:
let paymentsConfig = PaymentsConfig(
    apiKey: ProcessInfo.processInfo.environment["REVENUECAT_API_KEY"]!,
    entitlementID: ProcessInfo.processInfo.environment["RC_ENTITLEMENT_ID"] ?? "pro"
)

revenueCatClient.configure(paymentsConfig)

// 3. Inject into composition
self.paymentsClient = revenueCatClient

// RevenueCat automatically:
// - Syncs with App Store
// - Tracks subscription status
// - Handles cross-platform receipts
// - Emits state changes via AsyncStream

# From RevenueCat Dashboard → Project Settings → API Keys
REVENUECAT_API_KEY = appl_YOUR_KEY

# Entitlement ID from RevenueCat Dashboard
RC_ENTITLEMENT_ID = pro

// In PaywallViewModel
func purchase(productID: String) async {
    do {
        try await paymentsClient.purchase(productID: productID)
        // Success! State updates automatically
    } catch {
        // Handle error (cancelled, failed, etc.)
    }
}

// Restore previous purchases
func restorePurchases() async {
    do {
        try await paymentsClient.restorePurchases()
        // Subscriptions restored
    } catch {
        // Handle error
    }
}

// Check if user has pro access
let state = await paymentsClient.currentState()
if state.isSubscribed {
    // Show premium features
} else {
    // Show paywall
}

// In SettingsView
if !viewModel.isSubscribed {
    Button("Go Premium") {
        showPaywall = true
    }
}
.sheet(isPresented: $showPaywall) {
    PaywallView(viewModel: paywallViewModel)
}

// 1. Create product in App Store Connect
// 2. Import to RevenueCat
// 3. Update paywall UI to show new tier

// In PaywallView, add:
PricingCard(
    name: "Basic",
    price: "$4.99",
    period: "month",
    features: [
        "100 messages/day",
        "GPT-3.5 Turbo"
    ],
    action: { 
        await viewModel.purchase(productID: "basic_monthly") 
    }
)

// Check remaining usage
func canSendMessage() async -> Bool {
    let state = await paymentsClient.currentState()
    
    if state.isSubscribed {
        return true  // Unlimited for pro
    } else {
        let count = await messageRepository.todayCount()
        return count < 20  // Free tier limit
    }
}

// Multiple entitlements
if state.activeEntitlementIDs.contains("pro") {
    // Pro features
}

if state.activeEntitlementIDs.contains("premium_support") {
    // Priority support
}

class MockPaymentsClient: PaymentsClient {
    // Simulates subscription states
    // Perfect for UI testing
    // No App Store Connect needed
}