libnovel/ios/LibNovel/LibNovel/Extensions/NavDestination.swift

import SwiftUI

// MARK: - Navigation destination enum used across all tabs

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

// MARK: - View extensions for shared navigation + error alert patterns

extension View {
    /// Registers the app-wide navigation destinations for NavDestination values.
    /// Apply once per NavigationStack instead of repeating the switch in every tab.
    func appNavigationDestination() -> some View {
        modifier(AppNavigationDestinationModifier())
    }

    /// Presents a standard "Error" alert driven by an optional String binding.
    /// Dismissing the alert sets the binding back to nil.
    func errorAlert(_ error: Binding<String?>) -> some View {
        alert("Error", isPresented: Binding(
            get: { error.wrappedValue != nil },
            set: { if !$0 { error.wrappedValue = nil } }
        )) {
            Button("OK") { error.wrappedValue = nil }
        } message: {
            Text(error.wrappedValue ?? "")
        }
    }
}

// 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)
                    }
                }
                // Expose namespace to child views via environment
                .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)
                    }
                }
        }
    }
}

// MARK: - Environment key for 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: - Cover card zoom source modifier

/// Apply this to any cover image that should be a zoom source for book navigation.
/// Falls back to a no-op on iOS 17 or when no namespace is available.
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
        }
    }
}

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