import Foundation

/// Encapsulates the premium status sync state machine.
/// Extracted from ContentView to be independently testable.
@MainActor
final class PremiumSyncService {

    /// Injectable for testing — defaults to real StoreKit check.
    var hasActiveSubscription: () async -> Bool = {
        await StoreManager.hasActiveSubscription()
    }

    /// Determine whether the user should be premium after a sync.
    ///
    /// Rules:
    /// - Active subscription found  → always return `true` (upgrade).
    /// - No subscription, currently free → return `false`.
    /// - No subscription, currently premium, **cold launch** → return `false`
    ///   (subscription likely expired between sessions).
    /// - No subscription, currently premium, **foreground activation** → return `true`
    ///   (StoreKit `currentEntitlements` can return empty for a few seconds immediately
    ///   after a purchase while the receipt propagates; never downgrade mid-session).
    func sync(currentIsPremium: Bool, isColdLaunch: Bool) async -> Bool {
        let active = await hasActiveSubscription()
        switch (active, currentIsPremium, isColdLaunch) {
        case (true, _, _):
            return true
        case (false, false, _):
            return false
        case (false, true, true):
            return false   // Subscription expired → downgrade on cold launch
        case (false, true, false):
            return true    // Keep premium on foreground (timing protection)
        }
    }
}