// 添加一個(gè)請(qǐng)求攔截器
axios.interceptors.request.use(function (config) {
  // 在發(fā)送請(qǐng)求之前可以做一些事情
  return config;
}, function (error) {
  // 處理請(qǐng)求錯(cuò)誤
  return Promise.reject(error);
});
// 添加一個(gè)響應(yīng)攔截器
axios.interceptors.response.use(function (response) {
  // 處理響應(yīng)數(shù)據(jù)
  return response;
}, function (error) {
  // 處理響應(yīng)錯(cuò)誤
  return Promise.reject(error);
});

axios.interceptors.request.use(config => {
  config.headers.test += '1'
  return config
})
axios.interceptors.request.use(config => {
  config.headers.test += '2'
  return config
})

const myInterceptor = axios.interceptors.request.use(function () {/*...*/})
axios.interceptors.request.eject(myInterceptor)

export interface AxiosInterceptorManager<T> {
  use(resolved: ResolvedFn<T>, rejected?: RejectedFn): number
  eject(id: number): void
}
export interface ResolvedFn<T=any> {
  (val: T): T | Promise<T>
}
export interface RejectedFn {
  (error: any): any
}

import { ResolvedFn, RejectedFn } from '../types'
interface Interceptor<T> {
  resolved: ResolvedFn<T>
  rejected?: RejectedFn
}
export default class InterceptorManager<T> {
  private interceptors: Array<Interceptor<T> | null>
  constructor() {
    // 攔截器數(shù)組
    this.interceptors = []
  }
  // 收集攔截器  
  use(resolved: ResolvedFn<T>, rejected?: RejectedFn): number {
    this.interceptors.push({
      resolved,
      rejected
    })
    return this.interceptors.length - 1
  }
  // 遍歷用戶(hù)寫(xiě)的攔截器，并執(zhí)行fn函數(shù)把攔截器作為參數(shù)傳入
  forEach(fn: (interceptor: Interceptor<T>) => void): void {
    this.interceptors.forEach(interceptor => {
      if (interceptor !== null) {
        fn(interceptor)
      }
    })
  }
  eject(id: number): void {
    if (this.interceptors[id]) {
      // 置為null，不能直接刪除
      this.interceptors[id] = null
    }
  }
}

interface Interceptors {
  request: InterceptorManager<AxiosRequestConfig>
  response: InterceptorManager<AxiosResponse>
}
export default class Axios {
  interceptors: Interceptors
  constructor() {
    this.interceptors = {
      request: new InterceptorManager<AxiosRequestConfig>(),
      response: new InterceptorManager<AxiosResponse>()
    }
  }
}

interface PromiseChain {
  resolved: ResolvedFn | ((config: AxiosRequestConfig) => AxiosPromise)
  rejected?: RejectedFn
}
request(url: any, config?: any): AxiosPromise {
  if (typeof url === 'string') {
    if (!config) {
      config = {}
    }
    config.url = url
  } else {
    config = url
  }
  // 定義一個(gè)數(shù)組，這個(gè)數(shù)組就是要執(zhí)行的任務(wù)鏈，默認(rèn)有一個(gè)真正發(fā)送請(qǐng)求的任務(wù)
  const chain: PromiseChain[] = [{
    resolved: dispatchRequest,
    rejected: undefined
  }]
  // 把用戶(hù)定義的請(qǐng)求攔截器存放到任務(wù)鏈中，請(qǐng)求攔截器最后注冊(cè)的最先執(zhí)行，所以使用unshift方法
  this.interceptors.request.forEach(interceptor => {
    chain.unshift(interceptor)
  })
  // 把響應(yīng)攔截器存放到任務(wù)鏈中
  this.interceptors.response.forEach(interceptor => {
    chain.push(interceptor)
  })
  // 利用config初始化一個(gè)promise
  let promise = Promise.resolve(config)
  // 遍歷任務(wù)鏈
  while (chain.length) {
    // 取出任務(wù)鏈的首個(gè)任務(wù)
    const { resolved, rejected } = chain.shift()!
    // resolved的執(zhí)行時(shí)機(jī)是就是上一個(gè)promise執(zhí)行resolve()的時(shí)候，這樣就形成了鏈?zhǔn)秸{(diào)用
    promise = promise.then(resolved, rejected)
  }
  return promise
}