import { HttpRequest } from '@angular/common/http';
import { InjectionToken, Injector, Injectable } from '@angular/core';

export const NA_HTTP_INTERCEPTOR_PREPARABLE = new InjectionToken<NaHttpInterceptorPreparable[]>('NA_HTTP_INTERCEPTOR_PREPARABLE');

/**
 * HTTP请求拦截器前置处理器
 *
 * @export
 * @interface NaHttpInterceptorPreparable
 */
export interface NaHttpInterceptorPreparable {
  /**
   * 拦截器前置处理
   *
   * @param {HttpRequest<any>} req
   * @returns {HttpRequest<any>}
   * @memberof NaHttpInterceptorPreparable
   */
  prepare(req: HttpRequest<any>, next: NaHttpRequestHandler): HttpRequest<any>;
}

export abstract class NaHttpRequestHandler {
  abstract handle(req: HttpRequest<any>): HttpRequest<any>;
}

export class NaHttpInterceptorHandler implements NaHttpRequestHandler {
  constructor(private next: NaHttpRequestHandler, private preparable: NaHttpInterceptorPreparable) {}

  handle(req: HttpRequest<any>): HttpRequest<any> {
    return this.preparable.prepare(req, this.next);
  }
}

@Injectable()
export class NaHttpInterceptorPreparableHandler implements NaHttpRequestHandler {
  private chain: NaHttpRequestHandler | null = null;

  constructor(private injector: Injector) {}

  handle(req: HttpRequest<any>): HttpRequest<any> {
    if (this.chain === null) {
      const preparables = this.injector.get(NA_HTTP_INTERCEPTOR_PREPARABLE, []);
      this.chain = preparables.reduceRight((next, interceptor) => new NaHttpInterceptorHandler(next, interceptor), new DefaultNaHttpRequestHandler());
    }
    return this.chain.handle(req);
  }
}

export class DefaultNaHttpRequestHandler implements NaHttpRequestHandler {

  handle(req: HttpRequest<any>): HttpRequest<any> {
    return req;
  }
}