import Hummingbird

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

    public static func buildExpression(
        _ collection: RouteCollection<Context>
    ) -> [RouteCollection<Context>] {
        [collection]
    }

    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 }
    }

}

// MARK: - Helpers

public extension RouterMethods {

    // MARK: Methods

    /// Adds route collections to the router using the ``RouteCollectionBuilder`` result builder.
    ///
    /// Mirrors `addMiddleware`, letting controllers be listed declaratively:
    ///
    /// ```swift
    /// router.addRoutes {
    ///     RootController<AppRequestContext>().routes
    ///     HealthController<AppRequestContext>().routes
    /// }
    /// ```
    ///
    /// Each collection is added at the router's root, exactly as a sequence of
    /// `addRoutes(_:)` calls would.
    /// - Parameter build: the route-collection stack result builder.
    /// - Returns: the router, so calls can be chained.
    @discardableResult
    func addRoutes(
        @RouteCollectionBuilder<Context> _ build: () -> [RouteCollection<Context>]
    ) -> Self {
        for collection in build() {
            addRoutes(collection)
        }

        return self
    }

}