import Hummingbird

/// A result builder that collects the route collections of ``RouterController`` values into a stack.
///
/// Mirrors the `MiddlewareFixedTypeBuilder` Hummingbird uses for `addMiddleware`, letting controllers be listed declaratively rather than having
/// their routes added one statement at a time.
@resultBuilder
public enum RouteCollectionBuilder<Context: RequestContext> {

    public static func buildExpression(
        _ controller: some RouterController<Context>
    ) -> [RouteCollection<Context>] {
        [controller.routes]
    }

    public static func buildBlock(
        _ collections: [RouteCollection<Context>]...
    ) -> [RouteCollection<Context>] {
        collections.flatMap { $0 }
    }

    public static func buildOptional(
        _ collections: [RouteCollection<Context>]?
    ) -> [RouteCollection<Context>] {
        collections ?? []
    }

    public static func buildEither(
        first collections: [RouteCollection<Context>]
    ) -> [RouteCollection<Context>] {
        collections
    }

    public static func buildEither(
        second collections: [RouteCollection<Context>]
    ) -> [RouteCollection<Context>] {
        collections
    }

    public static func buildArray(
        _ collections: [[RouteCollection<Context>]]
    ) -> [RouteCollection<Context>] {
        collections.flatMap { $0 }
    }

}