import AppKit
import Combine
import Foundation
import StoreKit

enum PurchaseError: Equatable {
    case productsLoadTimeout
    case subscriptionUnavailable
    case planUnavailable
    case purchaseNotVerified
    case purchasePending
    case noActiveSubscriptions
    case generic

    var message: String {
        switch self {
        case .productsLoadTimeout:
            "Couldn't load subscription products right now. Check your StoreKit configuration / internet and try again."
        case .subscriptionUnavailable:
            "This subscription is currently unavailable. Please try again in a moment."
        case .planUnavailable:
            "This plan isn't available right now. Please try again later."
        case .purchaseNotVerified:
            "Apple couldn't verify this purchase."
        case .purchasePending:
            "This purchase is waiting for approval (for example, Ask to Buy)."
        case .noActiveSubscriptions:
            "No active subscriptions were found for this Apple ID."
        case .generic:
            "Something went wrong with your subscription. Please try again."
        }
    }
}

@MainActor
final class SubscriptionManager: ObservableObject {
    private enum ProductLoadError: Error {
        case timeout
    }

    @Published private(set) var productsByID: [String: Product] = [:]
    @Published private(set) var isLoadingProducts = false
    @Published private(set) var purchasingPlan: PaywallPlan?
    @Published private(set) var hasPremiumAccess = false
    @Published private(set) var hasResolvedPremiumStatus = false
    @Published var purchaseError: PurchaseError?

    var hasAllProductsLoaded: Bool {
        SubscriptionProductID.all.allSatisfy { productsByID[$0] != nil }
    }

    private var inFlightProductLoad: Task<Void, Never>?

    init() {
        Task { await listenForTransactionUpdates() }
        Task { await refreshPremiumAccess() }
        Task { await loadProducts(presentLoadingUI: false) }
    }

    func loadProducts(presentLoadingUI: Bool? = nil) async {
        if let existing = inFlightProductLoad {
            await existing.value
            return
        }

        let uiFlag = presentLoadingUI
        let task = Task { @MainActor in
            await performLoadProducts(presentLoadingUI: uiFlag)
        }
        inFlightProductLoad = task
        await task.value
        inFlightProductLoad = nil
    }

    func product(for plan: PaywallPlan) -> Product? {
        productsByID[plan.productID]
    }

    func mainPrice(for plan: PaywallPlan) -> String {
        product(for: plan)?.displayPrice ?? plan.fallbackMainPrice
    }

    func priceSuffix(for plan: PaywallPlan) -> String? {
        switch plan {
        case .monthly: "/mo"
        case .yearly: "/yr"
        case .lifetime: nil
        }
    }

    func billingDescription(for plan: PaywallPlan) -> String {
        guard let product = product(for: plan) else {
            return plan.fallbackBillingDescription
        }

        if let subscription = product.subscription,
           let intro = subscription.introductoryOffer,
           intro.paymentMode == .freeTrial {
            let trialPeriod = formattedPeriod(intro.period)
            let billingPeriod = formattedSubscriptionPeriod(subscription.subscriptionPeriod)
            return "\(trialPeriod) Free Trial, then \(product.displayPrice) per \(billingPeriod)"
        }

        switch plan {
        case .monthly:
            return "Billed at \(product.displayPrice) every month"
        case .yearly:
            return "Billed at \(product.displayPrice) every year"
        case .lifetime:
            return "One-time payment of \(product.displayPrice)"
        }
    }

    func purchase(_ plan: PaywallPlan) async -> Bool {
        purchaseError = nil

        var product = productsByID[plan.productID]
        if product == nil {
            await loadProducts(presentLoadingUI: false)
            product = productsByID[plan.productID]
        }

        guard let product else {
            let missingProductIDs = SubscriptionProductID.all.filter { productsByID[$0] == nil }
            if missingProductIDs.isEmpty {
                purchaseError = .subscriptionUnavailable
            } else {
                purchaseError = .planUnavailable
                #if DEBUG
                print(
                    """
                    [SubscriptionManager] Missing StoreKit products: \(missingProductIDs.joined(separator: ", "))
                    To test locally, attach `Paywall.storekit` in Xcode:
                    Product > Scheme > Edit Scheme > Run > Options > StoreKit Configuration.
                    """
                )
                #endif
            }
            return false
        }

        purchasingPlan = plan
        defer { purchasingPlan = nil }

        do {
            let result = try await product.purchase()
            switch result {
            case .success(let verification):
                guard case .verified(let transaction) = verification else {
                    purchaseError = .purchaseNotVerified
                    return false
                }
                await transaction.finish()
                await refreshPremiumAccess()
                return hasPremiumAccess
            case .userCancelled:
                return false
            case .pending:
                purchaseError = .purchasePending
                return false
            @unknown default:
                return false
            }
        } catch {
            purchaseError = .generic
            return false
        }
    }

    func openSubscriptionManagement() {
        guard let url = URL(string: "https://apps.apple.com/account/subscriptions") else { return }
        NSWorkspace.shared.open(url)
    }

    func restorePurchases() async {
        purchaseError = nil
        do {
            try await AppStore.sync()
            await refreshPremiumAccess()
            if !hasPremiumAccess {
                purchaseError = .noActiveSubscriptions
            }
        } catch {
            purchaseError = .generic
        }
    }

    private func performLoadProducts(presentLoadingUI: Bool?) async {
        let missingAny = SubscriptionProductID.all.contains { productsByID[$0] == nil }
        let shouldShowLoading = presentLoadingUI ?? missingAny

        if !missingAny, presentLoadingUI != true {
            purchaseError = nil
            await refreshPremiumAccess()
            return
        }

        if shouldShowLoading {
            isLoadingProducts = true
        }
        defer {
            if shouldShowLoading {
                isLoadingProducts = false
            }
        }

        purchaseError = nil
        do {
            let loaded = try await loadProductsWithTimeout(seconds: 12)
            var map: [String: Product] = [:]
            for product in loaded {
                map[product.id] = product
            }
            productsByID = map
            await refreshPremiumAccess()
        } catch is ProductLoadError {
            purchaseError = .productsLoadTimeout
        } catch {
            purchaseError = .generic
        }
    }

    private func loadProductsWithTimeout(seconds: TimeInterval) async throws -> [Product] {
        try await withThrowingTaskGroup(of: [Product].self) { group in
            group.addTask {
                try await Product.products(for: SubscriptionProductID.all)
            }
            group.addTask {
                let timeoutNanoseconds = UInt64(seconds * 1_000_000_000)
                try await Task.sleep(nanoseconds: timeoutNanoseconds)
                throw ProductLoadError.timeout
            }

            guard let first = try await group.next() else {
                throw ProductLoadError.timeout
            }
            group.cancelAll()
            return first
        }
    }

    private func refreshPremiumAccess() async {
        var hasPremium = false

        for await result in Transaction.currentEntitlements {
            guard case .verified(let transaction) = result else { continue }
            guard SubscriptionProductID.all.contains(transaction.productID) else { continue }
            guard transaction.revocationDate == nil else { continue }

            if let expirationDate = transaction.expirationDate, expirationDate < Date() {
                continue
            }

            hasPremium = true
            break
        }

        if !hasPremium {
            hasPremium = await hasActiveSubscriptionStatus()
        }

        #if DEBUG
        // Local Xcode runs should exercise AI tools without a StoreKit purchase.
        if !hasPremium {
            hasPremium = true
        }
        #endif

        hasPremiumAccess = hasPremium
        hasResolvedPremiumStatus = true
    }

    private func hasActiveSubscriptionStatus() async -> Bool {
        if productsByID.isEmpty {
            do {
                let loaded = try await Product.products(for: SubscriptionProductID.all)
                var map: [String: Product] = [:]
                for product in loaded { map[product.id] = product }
                productsByID = map
            } catch {
                return false
            }
        }

        for product in productsByID.values {
            guard let subscription = product.subscription else { continue }
            do {
                let statuses = try await subscription.status
                let isActive = statuses.contains { status in
                    switch status.state {
                    case .subscribed, .inGracePeriod, .inBillingRetryPeriod:
                        return true
                    case .expired, .revoked:
                        return false
                    default:
                        return false
                    }
                }
                if isActive { return true }
            } catch {
                continue
            }
        }

        return false
    }

    private func listenForTransactionUpdates() async {
        for await update in Transaction.updates {
            guard case .verified(let transaction) = update else { continue }
            await transaction.finish()
            await refreshPremiumAccess()
        }
    }

    private func formattedPeriod(_ period: Product.SubscriptionPeriod) -> String {
        switch period.unit {
        case .day where period.value == 1: "1 Day"
        case .day: "\(period.value) Days"
        case .week where period.value == 1: "1 Week"
        case .week: "\(period.value) Weeks"
        case .month where period.value == 1: "1 Month"
        case .month: "\(period.value) Months"
        case .year where period.value == 1: "1 Year"
        case .year: "\(period.value) Years"
        @unknown default: "\(period.value) Days"
        }
    }

    private func formattedSubscriptionPeriod(_ period: Product.SubscriptionPeriod) -> String {
        switch period.unit {
        case .day: period.value == 1 ? "day" : "\(period.value) days"
        case .week: period.value == 1 ? "week" : "\(period.value) weeks"
        case .month: period.value == 1 ? "month" : "\(period.value) months"
        case .year: period.value == 1 ? "year" : "\(period.value) years"
        @unknown default: "billing period"
        }
    }
}

// MARK: - App Rating

enum RatingPromptSource {
    case postPurchase
    case usageMilestone
}

@MainActor
final class AppRatingManager: ObservableObject {
    static let hasRatedKey = "hasRatedApp"
    static let hasShownUsagePromptKey = "hasShownUsageRatingPrompt"

    private static let continuousUsageThreshold: TimeInterval = 30 * 60

    @Published private(set) var showRatingPrompt = false
    @Published private(set) var ratingPromptSource: RatingPromptSource?

    private let defaults: UserDefaults
    private var isPremium = false
    private var continuousSessionStart: Date?
    private var usageTimerTask: Task<Void, Never>?
    private var cancellables = Set<AnyCancellable>()

    private var hasRatedApp: Bool {
        defaults.bool(forKey: Self.hasRatedKey)
    }

    private var hasShownUsagePrompt: Bool {
        defaults.bool(forKey: Self.hasShownUsagePromptKey)
    }

    init(defaults: UserDefaults = .standard) {
        self.defaults = defaults
        observeAppLifecycle()
    }

    func updatePremiumStatus(_ isPremium: Bool) {
        self.isPremium = isPremium

        guard isPremium, !hasRatedApp, !hasShownUsagePrompt else {
            pauseUsageTracking()
            return
        }

        if NSApplication.shared.isActive {
            beginContinuousUsageSession()
        }
    }

    func handleSubscriptionPurchased() {
        guard !hasRatedApp else { return }

        pauseUsageTracking()
        ratingPromptSource = .postPurchase
        showRatingPrompt = true
    }

    func userAcceptedRating() {
        showRatingPrompt = false
        ratingPromptSource = nil
        defaults.set(true, forKey: Self.hasRatedKey)
        pauseUsageTracking()
        requestAppStoreReview()
    }

    func userDeclinedRating() {
        let source = ratingPromptSource
        showRatingPrompt = false
        ratingPromptSource = nil

        if source == .usageMilestone {
            defaults.set(true, forKey: Self.hasShownUsagePromptKey)
            pauseUsageTracking()
            return
        }

        guard isPremium, !hasRatedApp, !hasShownUsagePrompt else { return }

        if NSApplication.shared.isActive {
            beginContinuousUsageSession()
        }
    }

    private func observeAppLifecycle() {
        NotificationCenter.default.publisher(for: NSApplication.didBecomeActiveNotification)
            .sink { [weak self] _ in
                self?.appDidBecomeActive()
            }
            .store(in: &cancellables)

        NotificationCenter.default.publisher(for: NSApplication.willResignActiveNotification)
            .sink { [weak self] _ in
                self?.appDidResignActive()
            }
            .store(in: &cancellables)
    }

    private func appDidBecomeActive() {
        guard isPremium, !hasRatedApp, !hasShownUsagePrompt, !showRatingPrompt else { return }
        beginContinuousUsageSession()
    }

    private func appDidResignActive() {
        pauseUsageTracking()
    }

    private func beginContinuousUsageSession() {
        guard isPremium, !hasRatedApp, !hasShownUsagePrompt, !showRatingPrompt else { return }

        continuousSessionStart = Date()
        startUsageTimer()
    }

    private func pauseUsageTracking() {
        continuousSessionStart = nil
        usageTimerTask?.cancel()
        usageTimerTask = nil
    }

    private func startUsageTimer() {
        usageTimerTask?.cancel()
        usageTimerTask = Task { [weak self] in
            while !Task.isCancelled {
                try? await Task.sleep(nanoseconds: 1_000_000_000)
                guard !Task.isCancelled else { break }
                self?.checkContinuousUsageThreshold()
            }
        }
    }

    private func checkContinuousUsageThreshold() {
        guard
            let sessionStart = continuousSessionStart,
            isPremium,
            !hasRatedApp,
            !hasShownUsagePrompt,
            !showRatingPrompt
        else {
            return
        }

        let elapsed = Date().timeIntervalSince(sessionStart)
        guard elapsed >= Self.continuousUsageThreshold else { return }

        pauseUsageTracking()
        defaults.set(true, forKey: Self.hasShownUsagePromptKey)
        ratingPromptSource = .usageMilestone
        showRatingPrompt = true
    }

    private func requestAppStoreReview() {
        SKStoreReviewController.requestReview()
    }
}