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// Copyright 2018-2024 the oak authors. All rights reserved. MIT license.
// deno-lint-ignore-file
import type { State } from "./application.ts";import type { Context } from "./context.ts";
/** A function for chaining middleware. */export type Next = () => Promise<unknown>;
/** Middleware are functions which are chained together to deal with * requests. */export interface Middleware<  S extends State = Record<string, any>,  T extends Context = Context<S>,> {  (context: T, next: Next): Promise<unknown> | unknown;}
/** Middleware objects allow encapsulation of middleware along with the ability * to initialize the middleware upon listen. */export interface MiddlewareObject<  S extends State = Record<string, any>,  T extends Context<S> = Context<S>,> {  /** Optional function for delayed initialization which will be called when   * the application starts listening. */  init?: () => Promise<unknown> | unknown;  /** The method to be called to handle the request. */  handleRequest(context: T, next: Next): Promise<unknown> | unknown;}
/** Type that represents {@linkcode Middleware} or * {@linkcode MiddlewareObject}. */export type MiddlewareOrMiddlewareObject<  S extends State = Record<string, any>,  T extends Context = Context<S>,> = Middleware<S, T> | MiddlewareObject<S, T>;
/** A type guard that returns true if the value is * {@linkcode MiddlewareObject}. */export function isMiddlewareObject<  S extends State = Record<string, any>,  T extends Context = Context<S>,>(value: MiddlewareOrMiddlewareObject<S, T>): value is MiddlewareObject<S, T> {  return value && typeof value === "object" && "handleRequest" in value;}
/** Compose multiple middleware functions into a single middleware function. */export function compose<  S extends State = Record<string, any>,  T extends Context = Context<S>,>(  middleware: MiddlewareOrMiddlewareObject<S, T>[],): (context: T, next?: Next) => Promise<unknown> {  return function composedMiddleware(    context: T,    next?: Next,  ): Promise<unknown> {    let index = -1;
    async function dispatch(i: number): Promise<void> {      if (i <= index) {        throw new Error("next() called multiple times.");      }      index = i;      let m: MiddlewareOrMiddlewareObject<S, T> | undefined = middleware[i];      let fn: Middleware<S, T> | undefined;      if (typeof m === "function") {        fn = m;      } else if (m && typeof m.handleRequest === "function") {        fn = (m as MiddlewareObject).handleRequest.bind(m);      }      if (i === middleware.length) {        fn = next;      }      if (!fn) {        return;      }      await fn(context, dispatch.bind(null, i + 1));    }
    return dispatch(0);  };}