import Adw
import Gtk

// MARK: - Destination Registry

/// Maps a destination value's dynamic type to the builder that renders it.
///
/// Registration happens at mount time: `.navigationDestination(for:)` looks the
/// registry up in the environment injected by the enclosing `NavigationView`.
/// A second registration for the same type replaces the first, so the innermost
/// (latest-mounted) declaration wins, matching SwiftUI.
@MainActor final class NavigationDestinationRegistry {
    private var builders: [ObjectIdentifier: (AnyHashable) -> [AnyView]] = [:]

    func register<D: Hashable>(_ type: D.Type, _ build: @escaping (D) -> [AnyView]) {
        builders[ObjectIdentifier(type)] = { erased in
            guard let value = erased.base as? D else { return [] }
            return build(value)
        }
    }

    /// The views for `value`, or `nil` when no builder is registered for its
    /// exact dynamic type.
    func build(_ value: AnyHashable) -> [AnyView]? {
        builders[ObjectIdentifier(type(of: value.base))]?(value)
    }
}

// MARK: - Environment slots

private enum NavigationDestinationsKey: EnvironmentKey {
    static var defaultValue: NavigationDestinationRegistry? { nil }
}

private enum NavigationPageKey: EnvironmentKey {
    static var defaultValue: Adw.NavigationPage? { nil }
}

extension EnvironmentValues {
    /// The destination registry of the innermost enclosing `NavigationView`.
    var navigationDestinations: NavigationDestinationRegistry? {
        get { self[NavigationDestinationsKey.self] }
        set { self[NavigationDestinationsKey.self] = newValue }
    }

    /// The `Adw.NavigationPage` this subtree is mounted into.
    var navigationPage: Adw.NavigationPage? {
        get { self[NavigationPageKey.self] }
        set { self[NavigationPageKey.self] = newValue }
    }
}

// MARK: - navigationDestination(for:destination:)

extension View {
    /// Associates a destination view with a presented data type, for use within
    /// the enclosing path-driven `NavigationView`.
    ///
    /// Registration happens when this view mounts, so a destination declared
    /// inside another destination is only available once that outer page has
    /// been pushed - the same lazy-registration caveat SwiftUI has.
    ///
    /// - Parameters:
    ///   - data: The exact type of value this destination renders. Lookup is by
    ///     dynamic type; subclasses are not matched.
    ///   - destination: Builds the page content from a value snapshot.
    /// - Returns: The receiver, unchanged, with the destination registered.
    public func navigationDestination<D: Hashable>(
        for data: D.Type,
        @ViewBuilder destination: @escaping (D) -> [AnyView]
    ) -> AnyView {
        AnyView(makeWidget: { ctx in
            ctx.environment.navigationDestinations?.register(data, destination)
            return AnyView(self).makeWidget(ctx)
        })
    }
}

// MARK: - navigationTitle

extension View {
    /// Sets the title of the `Adw.NavigationPage` this view is mounted into
    /// (static, applied once at mount).
    ///
    /// `Adw.HeaderBar` inside the page displays this title automatically, and
    /// the next page's back button uses it as its tooltip. No-op outside a
    /// `NavigationView` page.
    public func navigationTitle(_ title: String) -> AnyView {
        AnyView(makeWidget: { ctx in
            ctx.environment.navigationPage?.setTitle(title: title)
            return AnyView(self).makeWidget(ctx)
        })
    }

    /// Sets the page title, tracking a ``Binding``.
    public func navigationTitle(_ title: Binding<String>) -> AnyView {
        AnyView(makeWidget: { ctx in
            if let page = ctx.environment.navigationPage {
                page.setTitle(title: title.wrappedValue)
                ctx.registry.add(title.subscribe { [page] t in page.setTitle(title: t) })
            }
            return AnyView(self).makeWidget(ctx)
        })
    }

    /// Sets the page title from a tracked closure, re-evaluated when any
    /// `@State` or observable property it reads changes.
    public func navigationTitle(_ title: @escaping () -> String) -> AnyView {
        AnyView(makeWidget: { ctx in
            if let page = ctx.environment.navigationPage {
                let tracker = DependencyTracker { [page] in page.setTitle(title: title()) }
                tracker.run()
                ctx.registry.add(tracker)
            }
            return AnyView(self).makeWidget(ctx)
        })
    }
}