import Hummingbird

/// Serves the website's root routes.
///
/// The controller exposes its routes as a `RouteCollection` so they can be added to a router
/// (or a sub-group) by the application that composes it:
///
/// ```swift
/// router.addRoutes(RootController<AppRequestContext>().routes)
/// ```
///
/// - Note: `Context` is the request context the routes are resolved against, and must match the
///   context of the router the routes are added to.
public struct RootController<Context: LocalizedRequestContext>: Sendable {

    // MARK: Properties

    /// The landing page, rendered once per supported language and reused for every request.
    private let responses: LocalizedHTMLCollectionResponse

    // MARK: Initializers

    /// Creates a root controller.
    public init() {
        self.responses = .init { IndexPage(locale: $0) }
    }

    // MARK: Computed

    /// The routes served by the controller.
    ///
    /// Serves a `GET` request for the root path (`/`) by rendering the ``IndexPage`` in the
    /// language negotiated for the request.
    public var routes: RouteCollection<Context> {
        let routes = RouteCollection(context: Context.self)

        routes.get(
            .Root.index,
            use: index
        )

        return routes
    }

}

// MARK: - Helpers

private extension RootController {

    // MARK: Methods

    /// Handles a request for the landing page.
    ///
    /// Renders the ``IndexPage`` in the language stored on the context by ``LocalizationMiddleware``,
    /// falling back to the default language.
    /// - Parameters:
    ///   - request: the incoming request.
    ///   - context: the context the request is resolved against.
    /// - Returns: the cached ``IndexPage`` response for the context's language.
    @Sendable
    func index(
        request: Request,
        context: Context
    ) -> Response {
        responses.response(for: context.language)
    }

}

// MARK: - Constants

private extension RouterPath {
    /// A namespace for the ``RootController`` route paths.
    enum Root {
        /// The path of the landing page.
        static let index: RouterPath = "/"
    }
}