import SwiftUI

extension EnvironmentValues {
    /// Set on a list shown as a `NavigationSplitView` sidebar: what it
    /// selects opens in the detail column's stack. Nil in a plain stack.
    @Entry var sidebarSelection: Binding<AnyHashable?>?

    /// Appends a route to the enclosing stack's path. Screens that push
    /// from a button use it instead of `navigationDestination(item:)`,
    /// which puts any later value-link push underneath the pushed screen.
    @Entry var pushRoute: (any Hashable) -> Void = { _ in }
}

extension View {
    /// Lets screens in this stack push onto `path` with `pushRoute`.
    func pushesRoutes(into path: Binding<NavigationPath>) -> some View {
        environment(\.pushRoute) { path.wrappedValue.append($0) }
    }
}

/// A `List` whose rows select into `sidebarSelection` when there is one.
/// A value-based link in a sidebar only reaches the detail column's stack
/// through the list's selection.
struct RoutingList<Content: View>: View {
    @ViewBuilder let content: () -> Content
    @Environment(\.sidebarSelection) private var selection

    var body: some View {
        if let selection {
            List(selection: selection) { content() }
        } else {
            List { content() }
        }
    }
}

/// A `NavigationLink` in a stack; in a sidebar, a button that opens the
/// route in the detail column. For links outside the list, such as
/// toolbar items, which the list's selection does not cover.
struct RouteLink<Value: Hashable, Label: View>: View {
    let value: Value
    @ViewBuilder let label: () -> Label
    @Environment(\.sidebarSelection) private var selection

    var body: some View {
        if let selection {
            Button { selection.wrappedValue = AnyHashable(value) } label: { label() }
        } else {
            NavigationLink(value: value) { label() }
        }
    }
}