import Hummingbird
import Infrastructure

/// Keeps the site out of search engines: every response — pages, files, redirects, errors — is marked `X-Robots-Tag: noindex, nofollow`.
///
/// A header rather than `robots.txt`, which stays open on purpose: a crawler barred from a page never reads its `noindex`, and may still
/// list the bare URL from links elsewhere. A header also covers what carries no markup, such as the photos sellers upload.
public struct NoIndexMiddleware<Context: RequestContext>: RouterMiddleware {

    // MARK: Constants

    /// The directive stamped on every response.
    public static var directive: String { "noindex, nofollow" }

    // MARK: Initializers

    /// Creates the middleware.
    public init() {}

    // MARK: Methods

    public func handle(
        _ request: Request,
        context: Context,
        next: (Request, Context) async throws -> Response
    ) async throws -> Response {
        do {
            var response = try await next(request, context)

            response.headers[.robotsTag] = Self.directive

            return response
        } catch let error as HTTPError {
            // An error thrown past this point becomes a response further out: the mark travels with it.
            var error = error

            error.headers[.robotsTag] = Self.directive

            throw error
        }
    }

}