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// TypeScript port of koa-compose (https://github.com/koajs/compose)export type NextFunction = () => Promise<any>;
export type Middleware<T = any> = (context: T, next: NextFunction) => Promise<any>;
export function compose<T = any> (middleware: Middleware<T>[]) {  if (!Array.isArray(middleware)) {    throw new TypeError('Middleware stack must be an array!');  }
  for (const fn of middleware) {    if (typeof fn !== 'function') {      throw new TypeError('Middleware must be composed of functions!');    }  }
  return function (this: any, context: T, next?: Middleware<T>) {    // last called middleware #    let index: number = -1;
    return dispatch.call(this, 0);
    function dispatch (this: any, i: number): Promise<any> {      if (i <= index) {        return Promise.reject(new Error('next() called multiple times'));      }
      index = i;
      let fn: Middleware|undefined = middleware[i];
      if (i === middleware.length) {        fn = next;      }
      if (!fn) {        return Promise.resolve();      }
      try {        return Promise.resolve(fn.call(this, context, dispatch.bind(this, i + 1)));      } catch (err) {        return Promise.reject(err);      }    }  };}