import type { Layer } from "../layer/index.js";
import type { AnyService, Service } from "../service/index.js";
export type FromFnClosure<Next extends AnyService, Request, Response> = (req: Request, next: Next) => Promise<Response> | Response;
/**
 * Creates a layer from a function.
 *
 * @example
 * ```ts
 * import { fromFn } from "@taxum/core/middleware/from-fn";
 * import { m, Router } from "@taxum/core/routing";
 *
 * const router = new Router()
 *     .route("/", m.get(() => "Hello World))
 *     .layer(fromFn((req, next) => {
 *         // do something with `req`
 *
 *         const res = await next.invoke(req);
 *
 *         // do something with `res`
 *
 *         return res;
 *     }));
 * ```
 */
export declare const fromFn: <Next extends AnyService, Request, Response>(f: FromFnClosure<Next, Request, Response>) => FromFnLayer<Next, Request, Response>;
/**
 * A layer that wraps a service with a function.
 *
 * @see {@link fromFn}
 */
export declare class FromFnLayer<Next extends AnyService, Request, Response> implements Layer<Service<Request, Response>, Next> {
    private readonly f;
    /**
     * Creates a new {@link FromFnLayer}.
     */
    constructor(f: FromFnClosure<Next, Request, Response>);
    layer(inner: Next): Service<Request, Response>;
}