import AppKit
import StoreKit
import SwiftUI

struct PaywallView: View {
    @EnvironmentObject private var subscriptions: SubscriptionManager
    @ObservedObject private var paywallConfigService = PaywallConfigService.shared
    @Bindable var viewModel: PaywallViewModel
    var onDismiss: () -> Void

    private var config: PaywallConfig { paywallConfigService.config }

    private var isPurchasingSelectedPlan: Bool {
        subscriptions.purchasingPlan == viewModel.selectedPlan
    }

    private var buttonsBusy: Bool {
        subscriptions.purchasingPlan != nil || subscriptions.isRestoringPurchases
    }

    private var isPremium: Bool {
        subscriptions.hasPremiumAccess
    }

    private var hasProductLoadFailure: Bool {
        subscriptions.productLoadError != nil && !subscriptions.hasAllProductsLoaded
    }

    private var isProductReady: Bool {
        subscriptions.product(for: viewModel.selectedPlan) != nil
    }

    private var availablePlans: [PaywallPlan] {
        subscriptions.availablePaywallPlans
    }

    var body: some View {
        GeometryReader { geometry in
            let metrics = PaywallLayoutMetrics(size: geometry.size)

            ZStack {
                AppTheme.background
                    .ignoresSafeArea()

                VStack(spacing: metrics.sectionSpacing) {
                    header(metrics: metrics)
                    featuresSection(metrics: metrics)

                    if hasProductLoadFailure {
                        productsErrorSection(metrics: metrics)
                    } else {
                        pricingCards(metrics: metrics)
                    }

                    ctaSection(metrics: metrics)
                    Spacer(minLength: 0)
                    footerLinks(metrics: metrics)
                }
                .padding(.horizontal, metrics.horizontalInset)
                .padding(.top, metrics.topInset)
                .padding(.bottom, metrics.bottomInset)
                .frame(width: geometry.size.width, height: geometry.size.height, alignment: .top)

                if subscriptions.isLoadingProducts && !subscriptions.hasAllProductsLoaded && !hasProductLoadFailure {
                    AppTheme.scrim
                        .ignoresSafeArea()
                        .allowsHitTesting(false)
                    ProgressView()
                        .controlSize(.large)
                }

                if isPremium {
                    closeButton(metrics: metrics)
                }
            }
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .ignoresSafeArea()
        .task {
            await subscriptions.ensureEntitlementsResolved()
            if !subscriptions.hasAllProductsLoaded, !subscriptions.isLoadingProducts {
                await subscriptions.loadProducts(presentLoadingUI: true)
            }
            await subscriptions.refreshTrialEligibility()
            await paywallConfigService.refreshFromRemote()
            viewModel.syncSelectedPlan(with: availablePlans)
        }
        .onChange(of: subscriptions.hasEverPurchasedPremium) { _, _ in
            Task { await subscriptions.refreshTrialEligibility() }
            viewModel.syncSelectedPlan(with: availablePlans)
            if let eligiblePlan = config.trialEligiblePlan,
               subscriptions.trialDisplay(for: eligiblePlan) != nil {
                viewModel.selectPlan(eligiblePlan)
            }
        }
        .onChange(of: subscriptions.hasPremiumAccess) { _, _ in
            Task { await subscriptions.refreshTrialEligibility() }
        }
        .onChange(of: subscriptions.hasAllProductsLoaded) { _, loaded in
            if loaded {
                Task { await subscriptions.refreshTrialEligibility() }
            }
        }
        .onChange(of: subscriptions.trialDisplayByPlan) { _, _ in
            if let eligiblePlan = config.trialEligiblePlan,
               subscriptions.trialDisplay(for: eligiblePlan) != nil {
                viewModel.selectPlan(eligiblePlan)
            }
        }
        .onReceive(NotificationCenter.default.publisher(for: .paywallConfigDidUpdate)) { _ in }
        .alert(
            config.messages.purchaseFailedTitle,
            isPresented: Binding(
                get: { subscriptions.purchaseError != nil },
                set: { presented in
                    if !presented { subscriptions.purchaseError = nil }
                }
            )
        ) {
            Button(config.messages.alertOK, role: .cancel) {}
        } message: {
            Text(subscriptions.purchaseError.map { config.message(for: $0) } ?? "")
        }
    }

    private func closeButton(metrics: PaywallLayoutMetrics) -> some View {
        VStack {
            HStack {
                Spacer()
                Button(action: onDismiss) {
                    Image(systemName: "xmark")
                        .font(.system(size: metrics.closeButtonSize, weight: .medium))
                        .foregroundStyle(AppTheme.textSecondary)
                        .frame(width: metrics.closeButtonHitArea, height: metrics.closeButtonHitArea)
                        .background(
                            Circle()
                                .fill(AppTheme.cardBackground)
                                .overlay(
                                    Circle()
                                        .stroke(AppTheme.cardBorder, lineWidth: 1)
                                )
                        )
                }
                .buttonStyle(AppPlainButtonStyle())
                .help(config.closeButtonHelp)
            }
            Spacer()
        }
        .padding(.trailing, metrics.horizontalInset * 0.55)
        .padding(.top, metrics.topInset * 0.28)
    }

    private func header(metrics: PaywallLayoutMetrics) -> some View {
        VStack(spacing: metrics.headerSpacing) {
            Text(config.rightTitle)
                .font(.system(size: metrics.titleFontSize, weight: .bold))
                .foregroundStyle(AppTheme.textPrimary)

            Text(config.rightSubtitle)
                .font(.system(size: metrics.subtitleFontSize))
                .foregroundStyle(AppTheme.textSecondary)
                .multilineTextAlignment(.center)
                .frame(maxWidth: metrics.subtitleMaxWidth)
        }
        .frame(maxWidth: .infinity)
    }

    private func featuresSection(metrics: PaywallLayoutMetrics) -> some View {
        VStack(alignment: .leading, spacing: metrics.featureSectionSpacing) {
            Text(config.leftPanelTitle)
                .font(.system(size: metrics.sectionTitleFontSize, weight: .semibold))
                .foregroundStyle(AppTheme.textPrimary)

            LazyVGrid(columns: metrics.featureColumns, alignment: .leading, spacing: metrics.featureRowSpacing) {
                ForEach(Array(config.features.enumerated()), id: \.offset) { _, feature in
                    PaywallFeatureRow(title: feature, metrics: metrics)
                }
            }
        }
        .frame(maxWidth: .infinity, alignment: .leading)
    }

    private func productsErrorSection(metrics: PaywallLayoutMetrics) -> some View {
        VStack(spacing: metrics.ctaSpacing) {
            Text(subscriptions.productLoadError ?? config.messages.plansLoadFailed)
                .font(.system(size: metrics.footerNoteFontSize))
                .foregroundStyle(AppTheme.textSecondary)
                .multilineTextAlignment(.center)

            Button(subscriptions.isLoadingProducts ? config.messages.retrying : config.messages.retry) {
                Task { await subscriptions.loadProducts(presentLoadingUI: true) }
            }
            .buttonStyle(AppTextLinkButtonStyle())
            .font(.system(size: metrics.footerLinkFontSize))
            .foregroundStyle(AppTheme.textSecondary)
            .disabled(subscriptions.isLoadingProducts)
        }
        .frame(maxWidth: .infinity, minHeight: metrics.cardMinHeight)
    }

    private func pricingCards(metrics: PaywallLayoutMetrics) -> some View {
        HStack(alignment: .top, spacing: metrics.cardSpacing) {
            ForEach(availablePlans) { plan in
                PaywallPricingCard(
                    plan: plan,
                    config: config,
                    product: subscriptions.product(for: plan),
                    trial: subscriptions.trialDisplay(for: plan),
                    isSelected: viewModel.selectedPlan == plan,
                    metrics: metrics
                ) {
                    viewModel.selectPlan(plan)
                    subscriptions.purchaseError = nil
                }
            }
        }
        .frame(maxWidth: .infinity)
    }

    private func ctaSection(metrics: PaywallLayoutMetrics) -> some View {
        let selectedProduct = subscriptions.product(for: viewModel.selectedPlan)
        let selectedTrial = subscriptions.trialDisplay(for: viewModel.selectedPlan)
        let ctaDisabled = buttonsBusy || subscriptions.isLoadingProducts || !isProductReady || hasProductLoadFailure

        return VStack(spacing: metrics.ctaSpacing) {
            Text(
                viewModel.selectedPlan.localizedRenewalDisclosure(
                    from: selectedProduct,
                    config: config,
                    trial: selectedTrial
                )
            )
            .font(.system(size: metrics.footerNoteFontSize))
            .foregroundStyle(AppTheme.textTertiary)
            .multilineTextAlignment(.center)

            Button {
                Task {
                    let purchased = await subscriptions.purchase(viewModel.selectedPlan)
                    if purchased {
                        onDismiss()
                    }
                }
            } label: {
                HStack(spacing: 8) {
                    if isPurchasingSelectedPlan {
                        ProgressView()
                            .controlSize(.small)
                            .tint(Color(hex: 0x0B0E14))
                    }
                    Text(
                        viewModel.selectedPlan.localizedCTATitle(
                            from: selectedProduct,
                            config: config,
                            trial: selectedTrial
                        )
                    )
                    .font(.system(size: metrics.ctaFontSize, weight: .bold))
                    .foregroundStyle(Color(hex: 0x0B0E14))
                }
                .frame(maxWidth: .infinity)
                .padding(.vertical, metrics.ctaVerticalPadding)
                .background(
                    LinearGradient(
                        colors: [AppTheme.accentPurpleLight, AppTheme.accentTeal],
                        startPoint: .leading,
                        endPoint: .trailing
                    )
                )
                .clipShape(RoundedRectangle(cornerRadius: metrics.cornerRadius))
            }
            .buttonStyle(AppPrimaryButtonStyle())
            .disabled(ctaDisabled)
            .opacity(ctaDisabled ? 0.7 : 1)

            HStack(spacing: 6) {
                Image(systemName: "lock.fill")
                    .font(.system(size: metrics.footerNoteFontSize))
                Text(config.securePaymentNote)
                    .font(.system(size: metrics.footerNoteFontSize))
            }
            .foregroundStyle(AppTheme.textTertiary)
        }
    }

    private func footerLinks(metrics: PaywallLayoutMetrics) -> some View {
        HStack(spacing: 0) {
            if !isPremium {
                footerLink(config.footer.continueFree, metrics: metrics) {
                    onDismiss()
                }

                Spacer(minLength: metrics.footerLinkSpacing)
            } else if subscriptions.hasActiveSubscription {
                footerLink(config.footer.manageSubscription, metrics: metrics) {
                    subscriptions.openSubscriptionManagement()
                }

                Spacer(minLength: metrics.footerLinkSpacing)
            }

            footerLink(
                subscriptions.isRestoringPurchases ? config.messages.retrying : config.footer.restorePurchase,
                metrics: metrics
            ) {
                Task {
                    await subscriptions.restorePurchases()
                    if subscriptions.hasPremiumAccess {
                        onDismiss()
                    }
                }
            }
            .disabled(subscriptions.isRestoringPurchases)

            Spacer(minLength: metrics.footerLinkSpacing)

            footerLink(config.footer.privacyPolicy, metrics: metrics) {
                openExternalLink(config.urls.privacy)
            }

            Spacer(minLength: metrics.footerLinkSpacing)

            footerLink(config.footer.support, metrics: metrics) {
                openExternalLink(config.urls.support)
            }

            Spacer(minLength: metrics.footerLinkSpacing)

            footerLink(config.footer.termsOfService, metrics: metrics) {
                openExternalLink(config.urls.terms)
            }
        }
        .padding(.horizontal, metrics.footerLinksHorizontalInset)
        .frame(maxWidth: .infinity)
    }

    private func openExternalLink(_ urlString: String) {
        guard let url = URL(string: urlString) else { return }
        NSWorkspace.shared.open(url)
    }

    private func footerLink(_ title: String, metrics: PaywallLayoutMetrics, action: @escaping () -> Void) -> some View {
        Button(title, action: action)
            .buttonStyle(AppTextLinkButtonStyle())
            .font(.system(size: metrics.footerLinkFontSize))
            .foregroundStyle(AppTheme.textSecondary)
            .lineLimit(1)
            .minimumScaleFactor(0.8)
    }
}

// MARK: - Layout Metrics

private struct PaywallLayoutMetrics {
    let size: CGSize

    var horizontalInset: CGFloat { size.width * 0.06 }
    var topInset: CGFloat { size.height * 0.11 }
    var bottomInset: CGFloat { size.height * 0.05 }

    var sectionSpacing: CGFloat { size.height * 0.04 }
    var headerSpacing: CGFloat { size.height * 0.012 }
    var featureSectionSpacing: CGFloat { size.height * 0.018 }
    var featureRowSpacing: CGFloat { size.height * 0.016 }
    var cardSpacing: CGFloat { size.width * 0.018 }
    var ctaSpacing: CGFloat { size.height * 0.014 }
    var footerLinkSpacing: CGFloat { size.width * 0.018 }
    var footerLinksHorizontalInset: CGFloat { size.width * 0.035 }

    var titleFontSize: CGFloat { clamp(size.height * 0.043, min: 22, max: 36) }
    var subtitleFontSize: CGFloat { clamp(size.height * 0.02, min: 12, max: 16) }
    var sectionTitleFontSize: CGFloat { clamp(size.height * 0.018, min: 11, max: 14) }
    var featureFontSize: CGFloat { clamp(size.height * 0.017, min: 10, max: 13) }
    var ctaFontSize: CGFloat { clamp(size.height * 0.022, min: 13, max: 16) }
    var footerNoteFontSize: CGFloat { clamp(size.height * 0.015, min: 9, max: 12) }
    var footerLinkFontSize: CGFloat { clamp(size.height * 0.015, min: 9, max: 12) }

    var subtitleMaxWidth: CGFloat { size.width * 0.55 }
    var cardMinHeight: CGFloat { size.height * 0.32 }
    var cardPadding: CGFloat { size.width * 0.014 }
    var cornerRadius: CGFloat { clamp(size.height * 0.014, min: 8, max: 12) }
    var ctaVerticalPadding: CGFloat { size.height * 0.022 }
    var closeButtonSize: CGFloat { clamp(size.height * 0.016, min: 10, max: 14) }
    var closeButtonHitArea: CGFloat { clamp(size.height * 0.038, min: 28, max: 36) }

    var featureColumns: [GridItem] {
        [
            GridItem(.flexible(), spacing: featureRowSpacing),
            GridItem(.flexible(), spacing: featureRowSpacing),
            GridItem(.flexible(), spacing: featureRowSpacing),
        ]
    }

    private func clamp(_ value: CGFloat, min: CGFloat, max: CGFloat) -> CGFloat {
        Swift.min(Swift.max(value, min), max)
    }
}

// MARK: - Components

private struct PaywallFeatureRow: View {
    let title: String
    let metrics: PaywallLayoutMetrics

    var body: some View {
        HStack(spacing: 8) {
            Image(systemName: "checkmark")
                .font(.system(size: metrics.featureFontSize * 0.75, weight: .bold))
                .foregroundStyle(AppTheme.accentGreen)
                .frame(width: metrics.featureFontSize + 4)

            Text(title)
                .font(.system(size: metrics.featureFontSize))
                .foregroundStyle(AppTheme.textSecondary)
                .lineLimit(1)
                .minimumScaleFactor(0.85)
        }
    }
}

private struct PaywallPricingCard: View {
    let plan: PaywallPlan
    let config: PaywallConfig
    let product: Product?
    let trial: PaywallTrialDisplay?
    let isSelected: Bool
    let metrics: PaywallLayoutMetrics
    let onSelect: () -> Void

    private var planCopy: PaywallConfig.PlanCopy {
        plan.planCopy(from: config)
    }

    var body: some View {
        Button(action: onSelect) {
            VStack(alignment: .leading, spacing: 0) {
                Color.clear
                    .frame(height: metrics.cardPadding * 1.0)
                    .padding(.bottom, metrics.cardPadding * 0.15)

                Text(planCopy.title)
                    .font(.system(size: metrics.ctaFontSize, weight: .semibold))
                    .foregroundStyle(AppTheme.textPrimary)

                if product != nil {
                    Text(plan.localizedSubtitle(from: product, config: config, trial: trial))
                        .font(.system(size: metrics.featureFontSize * 0.85))
                        .foregroundStyle(AppTheme.textTertiary)
                        .fixedSize(horizontal: false, vertical: true)
                        .padding(.top, 2)
                }

                HStack(alignment: .firstTextBaseline, spacing: 2) {
                    Text(plan.localizedPrice(from: product, config: config))
                        .font(.system(size: metrics.titleFontSize * 0.85, weight: .bold))
                        .foregroundStyle(AppTheme.textPrimary)

                    if product != nil, let priceSuffix = planCopy.priceSuffix {
                        Text(priceSuffix)
                            .font(.system(size: metrics.featureFontSize))
                            .foregroundStyle(AppTheme.textSecondary)
                    }
                }
                .padding(.top, metrics.cardPadding)
                .padding(.bottom, metrics.cardPadding * 0.9)

                VStack(alignment: .leading, spacing: metrics.featureRowSpacing * 0.7) {
                    ForEach(planCopy.features, id: \.self) { feature in
                        HStack(alignment: .top, spacing: 8) {
                            Image(systemName: "checkmark")
                                .font(.system(size: metrics.featureFontSize * 0.75, weight: .bold))
                                .foregroundStyle(AppTheme.accentGreen)
                                .padding(.top, 2)

                            Text(feature)
                                .font(.system(size: metrics.featureFontSize * 0.92))
                                .foregroundStyle(AppTheme.textSecondary)
                                .fixedSize(horizontal: false, vertical: true)
                                .multilineTextAlignment(.leading)
                        }
                    }
                }

                Spacer(minLength: 0)
            }
            .padding(metrics.cardPadding)
            .frame(maxWidth: .infinity, minHeight: metrics.cardMinHeight, alignment: .topLeading)
            .background(
                RoundedRectangle(cornerRadius: metrics.cornerRadius)
                    .fill(AppTheme.cardBackground)
            )
            .overlay(
                RoundedRectangle(cornerRadius: metrics.cornerRadius)
                    .stroke(
                        isSelected ? AppTheme.accentTeal : AppTheme.cardBorder,
                        lineWidth: isSelected ? 2 : 1
                    )
            )
            .overlay(alignment: .topTrailing) {
                if let trial {
                    cardBadge(trial.badgeText)
                } else if let badge = planCopy.badge, plan == .lifetime {
                    cardBadge(badge)
                }
            }
        }
        .buttonStyle(AppPlainButtonStyle())
        .hoverCard(cornerRadius: metrics.cornerRadius, isSelected: isSelected)
    }

    private func cardBadge(_ text: String) -> some View {
        Text(text)
            .font(.system(size: metrics.featureFontSize * 0.75, weight: .bold))
            .foregroundStyle(Color(hex: 0x0B0E14))
            .padding(.horizontal, 10)
            .padding(.vertical, 4)
            .background(AppTheme.accentTeal)
            .clipShape(Capsule())
            .padding(.top, metrics.cardPadding * 0.65)
            .padding(.trailing, metrics.cardPadding * 0.65)
    }
}

#Preview {
    let subscriptions = SubscriptionManager()
    return PaywallView(viewModel: PaywallViewModel(), onDismiss: {})
        .environmentObject(subscriptions)
        .frame(width: AppWindow.width, height: AppWindow.height)
        .onAppear {
            subscriptions.start()
            PaywallConfigService.shared.start()
        }
}