import ManaCore
import SwiftUI

/// Top-Level-Switch: Login vs Haupt-App. Haupt-App ist eine TabBar mit
/// drei Tabs (Decks / Entdecken / Account).
struct RootView: View {
    @Environment(AuthClient.self) private var auth
    @State private var selectedTab: AppTab = .decks
    @State private var pendingDeepLinkSlug: String?
    @State private var showCreateDeck = false

    var body: some View {
        Group {
            switch auth.status {
            case .signedIn:
                mainTabs
                    .onOpenURL { url in handle(url: url) }
                    .onContinueUserActivity(NSUserActivityTypeBrowsingWeb) { activity in
                        if let url = activity.webpageURL { handle(url: url) }
                    }
            case .unknown, .signedOut, .signingIn, .error:
                LoginView()
            }
        }
        .task {
            await auth.ensureSignedIn()
        }
    }

    @ViewBuilder
    private var mainTabs: some View {
        TabView(selection: $selectedTab) {
            DeckListView(showCreate: $showCreateDeck)
                .tabItem { Label("Decks", systemImage: "rectangle.stack") }
                .tag(AppTab.decks)

            ExploreView(deepLinkSlug: $pendingDeepLinkSlug)
                .tabItem { Label("Entdecken", systemImage: "sparkles") }
                .tag(AppTab.explore)

            NavigationStack {
                AccountView()
            }
            .tabItem { Label("Account", systemImage: "person.crop.circle") }
            .tag(AppTab.account)
        }
        .decksCreateAccessory(visible: selectedTab == .decks) {
            showCreateDeck = true
        }
    }

    /// Universal-Link- und URL-Scheme-Handler:
    /// - `https://cardecky.mana.how/d/<slug>` → Explore-Tab + PublicDeckView
    /// - `cards://study/<deckId>` → später (β-6 Notifications)
    private func handle(url: URL) {
        Log.app.info("Open URL: \(url.absoluteString, privacy: .public)")
        if url.host == "cardecky.mana.how" || url.scheme == "cards" {
            let parts = url.pathComponents.filter { $0 != "/" }
            if parts.count >= 2, parts[0] == "d" {
                pendingDeepLinkSlug = parts[1]
                selectedTab = .explore
            }
        }
    }
}

enum AppTab: Hashable {
    case decks
    case explore
    case account
}

private extension View {
    /// iOS 26: floating „Neues Deck"-Pille via `.tabViewBottomAccessory`,
    /// nur sichtbar wenn der Decks-Tab aktiv ist. iOS 18 fällt auf den
    /// bestehenden `.bottomBar`-„+"-Toolbar-Button in `DeckListView` zurück.
    @ViewBuilder
    func decksCreateAccessory(visible: Bool, onTap: @escaping () -> Void) -> some View {
        if #available(iOS 26.0, *) {
            self.tabViewBottomAccessory {
                if visible {
                    DeckCreateAccessoryPill(action: onTap)
                }
            }
        } else {
            self
        }
    }
}

@available(iOS 26.0, *)
private struct DeckCreateAccessoryPill: View {
    let action: () -> Void

    var body: some View {
        Button(action: action) {
            Label("Neues Deck", systemImage: "plus")
                .font(.subheadline.weight(.semibold))
                .padding(.horizontal, 14)
                .padding(.vertical, 8)
        }
        .buttonStyle(.borderedProminent)
        .tint(CardsTheme.primary)
        .accessibilityLabel("Neues Deck erstellen")
    }
}