import SwiftUI
import CoreLocation
import UserNotifications
import Network

/// First-launch onboarding: introduces FuelBoard, walks the user through the
/// two system permissions (location and notifications) with in-context prompts,
/// then offers Best Value — explained, switched on or declined, and configured
/// with the same sliders Settings uses. Price data downloads over HTTPS with no
/// Local Network permission. In production it appears once at initial launch
/// (driven by `FuelStore.loadHasCompletedOnboarding()`); the Settings tab has a
/// row that re-opens it anytime.
///
/// The Best Value page itself lives in `BestValueIntroContent`, because the same
/// page is also shown to EXISTING users (once per announcement version, by
/// `BestValueIntroView`) — one source for its copy, controls and rules, so the
/// two can never drift apart.
struct OnboardingView: View {
    var onFinish: () -> Void

    @Environment(\.dismiss) private var dismiss
    @StateObject private var prompter = OnboardingPermissionPrompter()
    @State private var page = OnboardingView.initialPage()
    /// Best Value's own copy of the stored settings. Loaded so a replay starts
    /// from what the user already has; the shared page view saves on every
    /// change — the same immediate-persist rule as Settings — so a swipe past
    /// the page cannot lose a choice the user has already made.
    @State private var fuelSavings = OnboardingView.initialFuelSavings()

    private static let totalPages = 6

    var body: some View {
        VStack(spacing: 0) {
            // Top bar: page dots only — onboarding is mandatory, no skip.
            HStack {
                Spacer()
                HStack(spacing: 8) {
                    ForEach(0..<Self.totalPages, id: \.self) { index in
                        Circle()
                            .fill(index == page ? Color.accentColor : Color.gray.opacity(0.25))
                            .frame(width: 8, height: 8)
                    }
                }
                Spacer()
            }
            .padding(.horizontal, 20)
            .padding(.top, 12)

            TabView(selection: $page) {
                welcomePage.tag(0)
                locationPage.tag(1)
                notificationsPage.tag(2)
                dataPage.tag(3)
                bestValuePage.tag(4)
                donePage.tag(5)
            }
            .tabViewStyle(.page(indexDisplayMode: .never))

            bottomAction
                .padding(.horizontal, 20)
                .padding(.bottom, 24)
        }
        // Auto-advance once the user grants a permission.
        .onChange(of: prompter.locationGranted) { _, granted in
            if granted, page == 1 { page = 2 }
        }
        .onChange(of: prompter.notificationsGranted) { _, granted in
            if granted, page == 2 { page = 3 }
        }
        // Fire each permission when the user LEAVES its page by advancing
        // forward (swipe or Continue) — by then the screen has been read.
        // Never on arrival: a fast swipe can't stack prompts before a page
        // is seen. Forward-only: swiping back never fires. Idempotent —
        // an already-determined permission just refreshes, so the
        // auto-advance path and replays stay clean (no duplicate alerts).
        .onChange(of: page) { oldPage, newPage in
            guard newPage > oldPage else { return }
            if oldPage == 1 {
                prompter.requestLocation()
            } else if oldPage == 2 {
                prompter.requestNotifications()
            }
        }
        // No data-permission step: prices download from the internet (GitHub
        // mirror) with no permission at all — Local Network was removed from
        // the app when the relay left the consumer chain.
        .background(
            LinearGradient(
                colors: [Color(.systemBackground), Color.accentColor.opacity(0.06)],
                startPoint: .top, endPoint: .bottom
            )
            .ignoresSafeArea()
        )
    }

    // MARK: - Pages

    private var welcomePage: some View {
        VStack(spacing: 0) {
            Spacer()
            AnimatedOnboardingIcon(tint: .accentColor) {
                // The app icon itself, with the standard iOS rounded-corner
                // treatment (~22% of the size), so onboarding matches the
                // Home Screen.
                Image("AppIconArtwork")
                    .resizable()
                    .scaledToFill()
                    .frame(width: 96, height: 96)
                    .clipShape(RoundedRectangle(cornerRadius: 21, style: .continuous))
            }
            .padding(.bottom, 28)

            Text(String(localized: "Welcome to FuelBoard", comment: "Onboarding welcome title"))
                .font(.largeTitle.bold())
                .multilineTextAlignment(.center)

            Text(String(localized: "The cheapest petrol, diesel and premium fuel near you — from the official UK Fuel Finder data.", comment: "Onboarding welcome subtitle"))
                .font(.body)
                .foregroundStyle(.secondary)
                .multilineTextAlignment(.center)
                .padding(.horizontal, 32)
                .padding(.top, 12)

            featureRow(icon: "globe.europe.africa.fill", text: String(localized: "UK-wide prices — 8,000+ stations, updated twice a day", comment: "Onboarding feature row"))
            featureRow(icon: "scope", text: String(localized: "Cheapest within your chosen radius, or closest station first", comment: "Onboarding feature row"))
            featureRow(icon: "star.fill", text: String(localized: "Favourites with instant price comparison", comment: "Onboarding feature row"))
            featureRow(icon: "chart.bar.fill", text: String(localized: "Green/amber/red rating vs the best nearby price", comment: "Onboarding feature row"))
            featureRow(icon: "square.grid.2x2.fill", text: String(localized: "Home-screen widget showing the cheapest nearby", comment: "Onboarding feature row"))
            featureRow(icon: "bell.fill", text: String(localized: "Alerts when you approach the cheapest station", comment: "Onboarding feature row"))

            Spacer()
        }
    }

    private var locationPage: some View {
        VStack(spacing: 0) {
            Spacer()
            AnimatedOnboardingIcon(tint: .blue, motion: .locationArrow) {
                Image(systemName: "location.fill")
                    .font(.system(size: 40, weight: .semibold))
                    .foregroundStyle(.blue)
            }
            .padding(.bottom, 28)

            Text(String(localized: "Prices near you", comment: "Onboarding location permission title"))
                .font(.largeTitle.bold())

            Text(String(localized: "FuelBoard uses your location to show prices around you and rank stations by distance. Your position never leaves the device.", comment: "Onboarding location permission explanation"))
                .font(.body)
                .foregroundStyle(.secondary)
                .multilineTextAlignment(.center)
                .padding(.horizontal, 32)
                .padding(.top, 12)

            permissionStatusLabel(
                granted: prompter.locationGranted,
                denied: prompter.locationDenied,
                deniedText: String(localized: "Location was denied. You can still browse all stations, but \"nearest\" sorting needs it.", comment: "Onboarding location denied text")
            )
            .padding(.top, 24)

            Spacer()
        }
    }

    private var notificationsPage: some View {
        VStack(spacing: 0) {
            Spacer()
            AnimatedOnboardingIcon(tint: .orange, motion: .alarmBell) {
                Image(systemName: "bell.badge.fill")
                    .font(.system(size: 40, weight: .semibold))
                    .foregroundStyle(.orange)
            }
            .padding(.bottom, 28)

            Text(String(localized: "Cheapest-station alerts", comment: "Onboarding notifications title"))
                .font(.largeTitle.bold())

            Text(String(localized: "FuelBoard can notify you when you're approaching the cheapest station in your alert radius — even with the app closed. You can switch this off in the Alerts tab.", comment: "Onboarding notifications explanation"))
                .font(.body)
                .foregroundStyle(.secondary)
                .multilineTextAlignment(.center)
                .padding(.horizontal, 32)
                .padding(.top, 12)

            permissionStatusLabel(
                granted: prompter.notificationsGranted,
                denied: prompter.notificationsDenied,
                deniedText: String(localized: "Notifications were denied — you can still use FuelBoard, just without alert banners.", comment: "Onboarding notifications denied text")
            )
            .padding(.top, 24)

            Spacer()
        }
    }

    private var dataPage: some View {
        VStack(spacing: 0) {
            Spacer()
            AnimatedOnboardingIcon(tint: .teal, motion: .downloadArrow) {
                Image(systemName: "arrow.down.circle.fill")
                    .font(.system(size: 40, weight: .semibold))
                    .foregroundStyle(.teal)
            }
            .padding(.bottom, 28)

            Text(String(localized: "Prices, ready when you are", comment: "Onboarding data title"))
                .font(.largeTitle.bold())

            Text(String(localized: "FuelBoard downloads the latest prices from the internet automatically — the full UK dataset, refreshed twice a day. No extra permissions needed.", comment: "Onboarding data explanation"))
                .font(.body)
                .foregroundStyle(.secondary)
                .multilineTextAlignment(.center)
                .padding(.horizontal, 32)
                .padding(.top, 12)

            Spacer()
        }
    }

    /// The Best Value page — the shared body, so the first-run page and the
    /// announcement existing users see can never drift apart.
    private var bestValuePage: some View {
        BestValueIntroContent(settings: $fuelSavings)
    }

    private var donePage: some View {
        VStack(spacing: 0) {
            Spacer()
            ZStack {
                Circle()
                    .fill(LinearGradient(colors: [.green, .mint], startPoint: .topLeading, endPoint: .bottomTrailing))
                    .frame(width: 96, height: 96)
                Image(systemName: "checkmark")
                    .font(.system(size: 44, weight: .bold))
                    .foregroundStyle(.white)
            }
            .padding(.bottom, 28)

            Text(String(localized: "You're all set", comment: "Onboarding final title"))
                .font(.largeTitle.bold())

            Text(String(localized: "Find your cheapest fuel, add favourites, drop the widget on your Home Screen, and let alerts point you to the best price nearby.", comment: "Onboarding final explanation"))
                .font(.body)
                .foregroundStyle(.secondary)
                .multilineTextAlignment(.center)
                .padding(.horizontal, 32)
                .padding(.top, 12)

            Spacer()
        }
    }

    // MARK: - Bottom action

    @ViewBuilder
    private var bottomAction: some View {
        switch page {
        case 0:
            primaryButton(String(localized: "Continue", comment: "Onboarding continue button")) { page = 1 }
        case 1:
            primaryButton(String(localized: "Continue", comment: "Onboarding continue button")) {
                if prompter.locationDenied {
                    openSettings()
                } else if prompter.locationGranted {
                    page = 2  // already decided — just move on
                } else {
                    // Fire the system prompt NOW, while this page is still on
                    // screen (after it's been read) and BEFORE advancing — so
                    // the prompt never covers the next page's animation. Auto-
                    // advance on grant moves us on once the user responds;
                    // denying leaves the page's Settings path.
                    prompter.requestLocation()
                }
            }
        case 2:
            primaryButton(String(localized: "Continue", comment: "Onboarding continue button")) {
                if prompter.notificationsDenied || prompter.notificationsGranted {
                    page = 3  // decided either way — move on
                } else {
                    // Same rule as Location: prompt now, before advancing.
                    prompter.requestNotifications()
                }
            }
        case 3:
            // No permission on this page — prices need none. Straight on.
            primaryButton(String(localized: "Continue", comment: "Onboarding continue button")) { page = 4 }
        case 4:
            // Best Value: the settings were saved when the toggle moved, so a
            // swipe past this page keeps the choice.
            primaryButton(BestValueIntroContent.primaryTitle) { page = 5 }
        default:
            primaryButton(String(localized: "Start Using FuelBoard", comment: "Finish onboarding button")) { finish() }
        }
    }

    private func primaryButton(_ title: String, action: @escaping () -> Void) -> some View {
        OnboardingPrimaryButton(title: title, action: action)
    }

    private func featureRow(icon: String, text: String) -> some View {
        HStack(spacing: 12) {
            Image(systemName: icon)
                .font(.system(size: 20, weight: .semibold))
                .foregroundStyle(Color.accentColor)
                .frame(width: 32)
            Text(text)
                .font(.subheadline)
            Spacer(minLength: 0)
        }
        .padding(.horizontal, 36)
        .padding(.vertical, 10)
    }

    private func permissionStatusLabel(granted: Bool, denied: Bool, deniedText: String) -> some View {
        Group {
            if granted {
                Label(String(localized: "Allowed", comment: "Permission granted status"), systemImage: "checkmark.circle.fill")
                    .foregroundStyle(.green)
            } else if denied {
                Text(deniedText)
                    .font(.footnote)
                    .foregroundStyle(.secondary)
                    .multilineTextAlignment(.center)
                    .padding(.horizontal, 32)
            } else {
                Text(String(localized: "The system prompt will appear next.", comment: "Permission prompt pending status"))
                    .font(.footnote)
                    .foregroundStyle(.secondary)
            }
        }
        .font(.subheadline)
    }

    private func openSettings() {
        if let url = URL(string: UIApplication.openSettingsURLString) {
            UIApplication.shared.open(url)
        }
    }

    private func finish() {
        // Anyone who goes through the whole of onboarding has now seen the Best
        // Value page — mark the announcement seen so they don't immediately get
        // the standalone one aimed at existing users.
        FuelStore.markBestValueIntroSeen()
        FuelStore.saveHasCompletedOnboarding(true)
        onFinish()
    }

    // MARK: - QA hooks

    /// DEBUG-only launch args in the same spirit as ContentView's `-tab` and
    /// `-skipOnboarding`, both no-ops in release:
    ///
    /// - `-onboardingPage 4` opens straight on a page, so the screenshot harness
    ///   can photograph a page it cannot swipe or tap its way to.
    /// - `-onboardingBestValue on|off` forces the Best Value page's choice, so
    ///   both of its states can be captured without driving the toggle.
    private static func initialPage() -> Int {
        #if DEBUG
        let args = ProcessInfo.processInfo.arguments
        if let index = args.firstIndex(of: "-onboardingPage"),
           index + 1 < args.count,
           let value = Int(args[index + 1]),
           (0..<totalPages).contains(value) {
            return value
        }
        #endif
        return 0
    }

    private static func initialFuelSavings() -> FuelSavingsSettings {
        var settings = FuelStore.loadFuelSavingsSettings()
        #if DEBUG
        let args = ProcessInfo.processInfo.arguments
        if let index = args.firstIndex(of: "-onboardingBestValue"), index + 1 < args.count {
            settings.enabled = args[index + 1].lowercased() == "on"
        }
        #endif
        return settings
    }
}

/// The animated badge behind each page's icon. Internal rather than private
/// because `BestValueIntroContent` lives in its own file and uses it too.
struct AnimatedOnboardingIcon<Content: View>: View {
    enum Motion {
        case gentle
        case locationArrow
        case alarmBell
        case downloadArrow
    }

    let tint: Color
    var motion: Motion = .gentle
    @ViewBuilder var content: Content

    @State private var settled = false
    @State private var iconRotation: Double = 0
    @State private var iconOffsetY: CGFloat = 0
    @State private var iconScale: CGFloat = 0.92

    var body: some View {
        ZStack {
            Circle()
                .fill(tint.opacity(0.10))
                .frame(width: 108, height: 108)
                .scaleEffect(settled ? 1.0 : 0.94)

            Circle()
                .stroke(tint.opacity(0.18), lineWidth: 1)
                .frame(width: 118, height: 118)
                .scaleEffect(settled ? 1.03 : 0.97)
                .opacity(settled ? 1.0 : 0.55)

            content
                .scaleEffect(iconScale)
                .rotationEffect(.degrees(iconRotation))
                .offset(y: iconOffsetY)
        }
        .shadow(color: tint.opacity(0.12), radius: settled ? 12 : 4, y: settled ? 6 : 2)
        .animation(.spring(response: 0.55, dampingFraction: 0.82), value: settled)
        .onAppear {
            playAnimation()
        }
    }

    private func playAnimation() {
        settled = false
        iconRotation = 0
        iconOffsetY = 4
        iconScale = 0.92

        switch motion {
        case .gentle:
            withAnimation(.spring(response: 0.55, dampingFraction: 0.82)) {
                settled = true
                iconOffsetY = 0
                iconScale = 1.0
            }

        case .locationArrow:
            iconRotation = -120
            withAnimation(.linear(duration: 0.45)) {
                settled = true
                iconRotation = 24
                iconOffsetY = 0
                iconScale = 1.02
            }
            withAnimation(.spring(response: 0.45, dampingFraction: 0.62).delay(0.45)) {
                iconRotation = 0
                iconScale = 1.0
            }

        case .alarmBell:
            settled = true
            iconOffsetY = 0
            iconScale = 1.0
            withAnimation(.linear(duration: 0.10)) { iconRotation = -14 }
            withAnimation(.linear(duration: 0.10).delay(0.10)) { iconRotation = 14 }
            withAnimation(.linear(duration: 0.10).delay(0.20)) { iconRotation = -10 }
            withAnimation(.linear(duration: 0.10).delay(0.30)) { iconRotation = 10 }
            withAnimation(.spring(response: 0.34, dampingFraction: 0.72).delay(0.40)) { iconRotation = 0 }

        case .downloadArrow:
            iconOffsetY = -22
            withAnimation(.easeIn(duration: 0.22)) {
                settled = true
                iconScale = 1.0
                iconOffsetY = 8
            }
            withAnimation(.spring(response: 0.42, dampingFraction: 0.62).delay(0.22)) {
                iconOffsetY = 0
            }
        }
    }
}

/// Owns the system permission requests during onboarding and publishes
/// their outcomes so the pages can reflect them live.
@MainActor
final class OnboardingPermissionPrompter: NSObject, ObservableObject, CLLocationManagerDelegate {
    @Published private(set) var locationGranted = false
    @Published private(set) var locationDenied = false
    @Published private(set) var notificationsGranted = false
    @Published private(set) var notificationsDenied = false

    private let manager = CLLocationManager()

    override init() {
        super.init()
        manager.delegate = self
        refreshLocationStatus()
        refreshNotificationStatus()
    }

    func requestLocation() {
        switch manager.authorizationStatus {
        case .notDetermined:
            manager.requestWhenInUseAuthorization()
        default:
            refreshLocationStatus()
        }
    }

    func requestNotifications() {
        UNUserNotificationCenter.current().getNotificationSettings { settings in
            Task { @MainActor in
                switch settings.authorizationStatus {
                case .notDetermined:
                    do {
                        let granted = try await UNUserNotificationCenter.current()
                            .requestAuthorization(options: [.alert, .sound, .badge])
                        self.notificationsGranted = granted
                        self.notificationsDenied = !granted
                    } catch {
                        self.notificationsGranted = false
                        self.notificationsDenied = true
                    }
                case .authorized:
                    self.notificationsGranted = true
                    self.notificationsDenied = false
                default:
                    self.notificationsGranted = false
                    self.notificationsDenied = true
                }
            }
        }
    }

    /// Replay pre-flight: NO data permission exists anymore — prices download
    /// from the internet with no prompt, so there is nothing to preflight.
    /// (The LAN relay left the consumer chain; Local Network is gone.)

    nonisolated func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
        Task { @MainActor in
            self.refreshLocationStatus()
        }
    }

    private func refreshLocationStatus() {
        switch manager.authorizationStatus {
        case .authorizedWhenInUse, .authorizedAlways:
            locationGranted = true
            locationDenied = false
        case .denied, .restricted:
            locationGranted = false
            locationDenied = true
        default:
            locationGranted = false
            locationDenied = false
        }
    }

    private func refreshNotificationStatus() {
        UNUserNotificationCenter.current().getNotificationSettings { settings in
            Task { @MainActor in
                switch settings.authorizationStatus {
                case .authorized:
                    self.notificationsGranted = true
                    self.notificationsDenied = false
                case .denied, .provisional, .ephemeral:
                    self.notificationsGranted = settings.authorizationStatus == .provisional
                    self.notificationsDenied = !self.notificationsGranted
                default:
                    break
                }
            }
        }
    }
}