import SwiftUI

// MARK: - Navigation destination enum

enum NavDestination: Hashable {
    case book(String)               // slug
    case chapter(String, Int)       // slug + chapter number
    case userProfile(String)        // username
    case browseCategory(sort: String, genre: String, status: String, title: String)
}

// MARK: - View helpers

extension View {
    /// Registers app-wide navigationDestination for NavDestination values.
    /// Apply once per NavigationStack.
    func appNavigationDestination() -> some View {
        modifier(AppNavigationDestinationModifier())
    }

    /// Standard "Error" alert driven by an optional String binding.
    /// Suppresses network errors silently when offline (banner handles them).
    func errorAlert(_ error: Binding<String?>) -> some View {
        modifier(ErrorAlertModifier(error: error))
    }

    /// Signal to the root overlay that the mini player should be hidden.
    func hideMiniPlayer() -> some View {
        preference(key: HideMiniPlayerKey.self, value: true)
    }

    /// Marks a cover image as the zoom source for a book navigation transition (iOS 18+).
    func bookCoverZoomSource(slug: String) -> some View {
        modifier(BookCoverZoomSource(slug: slug))
    }
}

// MARK: - Error alert modifier

private struct ErrorAlertModifier: ViewModifier {
    @Binding var error: String?
    @EnvironmentObject var networkMonitor: NetworkMonitor

    private var shouldShowAlert: Bool {
        guard let msg = error else { return false }
        if !networkMonitor.isConnected {
            let keywords = ["internet", "offline", "network", "connection", "unreachable", "timed out", "no data"]
            if keywords.contains(where: { msg.lowercased().contains($0) }) {
                DispatchQueue.main.async { self.error = nil }
                return false
            }
        }
        return true
    }

    func body(content: Content) -> some View {
        content.alert("Error", isPresented: Binding(
            get:  { shouldShowAlert },
            set:  { if !$0 { error = nil } }
        )) {
            Button("OK") { error = nil }
        } message: {
            Text(error ?? "")
        }
    }
}

// MARK: - Navigation destination modifier

private struct AppNavigationDestinationModifier: ViewModifier {
    @Namespace private var zoomNamespace

    func body(content: Content) -> some View {
        if #available(iOS 18.0, *) {
            content
                .navigationDestination(for: NavDestination.self) { dest in
                    switch dest {
                    case .book(let slug):
                        BookDetailView(slug: slug)
                            .navigationTransition(.zoom(sourceID: slug, in: zoomNamespace))
                    case .chapter(let slug, let n):
                        ChapterReaderView(slug: slug, chapterNumber: n)
                    case .userProfile(let username):
                        UserProfileView(username: username)
                    case .browseCategory(let sort, let genre, let status, let title):
                        BrowseCategoryView(sort: sort, genre: genre, status: status, title: title)
                    }
                }
                .environment(\.bookZoomNamespace, zoomNamespace)
        } else {
            content
                .navigationDestination(for: NavDestination.self) { dest in
                    switch dest {
                    case .book(let slug):           BookDetailView(slug: slug)
                    case .chapter(let slug, let n): ChapterReaderView(slug: slug, chapterNumber: n)
                    case .userProfile(let username): UserProfileView(username: username)
                    case .browseCategory(let sort, let genre, let status, let title):
                        BrowseCategoryView(sort: sort, genre: genre, status: status, title: title)
                    }
                }
        }
    }
}

// MARK: - Environment key: zoom namespace

struct BookZoomNamespaceKey: EnvironmentKey {
    static var defaultValue: Namespace.ID? { nil }
}

extension EnvironmentValues {
    var bookZoomNamespace: Namespace.ID? {
        get { self[BookZoomNamespaceKey.self] }
        set { self[BookZoomNamespaceKey.self] = newValue }
    }
}

// MARK: - Preference key: hide mini player

struct HideMiniPlayerKey: PreferenceKey {
    static var defaultValue = false
    static func reduce(value: inout Bool, nextValue: () -> Bool) { value = value || nextValue() }
}

// MARK: - Cover zoom source modifier

struct BookCoverZoomSource: ViewModifier {
    let slug: String
    @Environment(\.bookZoomNamespace) private var namespace

    func body(content: Content) -> some View {
        if #available(iOS 18.0, *), let ns = namespace {
            content.matchedTransitionSource(id: slug, in: ns)
        } else {
            content
        }
    }
}