class Promise{
  constructor(excutor){
    this.value = '';
    this.reason = '';
    this.status = 'padding'
    this.onFulfilledCallback = []
    this.onRejectedCallback = []
    let resolve = (value)=>{
      /*2.這個(gè)判斷是為了status不可逆 只能從 padding轉(zhuǎn)化為 成功或者失敗*/
      if (this.status == 'padding') {
        this.status = 'fulfilled'
        this.value = value
        /*3.當(dāng)轉(zhuǎn)態(tài)改變的時(shí)候依次執(zhí)行隊(duì)列里面儲存的then函數(shù)里面對應(yīng)的回調(diào)*/
        this.onFulfilledCallback.forEach(fn=>{
          fn()
        })
      }
    };
    let reject = (reason)=>{
      /*2.這個(gè)判斷是為了status不可逆 只能從 padding轉(zhuǎn)化為 成功或者失敗*/
      if (this.status == 'padding') {
        this.status = 'rejected'
        this.reason = reason
        /*3.當(dāng)轉(zhuǎn)態(tài)改變的時(shí)候依次執(zhí)行隊(duì)列里面儲存的then函數(shù)里面對應(yīng)的回調(diào)*/
        this.onRejectedCallback.forEach(fn=>{
          fn()
        })
      }
    };
    /*1. 當(dāng)發(fā)生異常是捕獲異常 */
    try{
      excutor(resolve,reject)
    }catch (e){
      reject(e)
    }

  }
  then(onFulfilled,onRejected){
    //4.防止使用者不傳成功或失敗回調(diào)函數(shù)，所以成功失敗回調(diào)都給了默認(rèn)回調(diào)函數(shù)
    onFulfilled = typeof onFulfilled === "function" ? onFulfilled : value => value;
    onRejected = typeof onRejected === "function" ? onRejected : error => { throw error };
    let newPromise;
    if(this.status == 'fulfilled'){
      return newPromise = new Promise((resolve,reject)=>{
        setTimeout(()=>{
          try{
            let x = onFulfilled(this.value)
            this.resolvePromise(newPromise, x, resolve, reject);
          }catch (e){
            reject(e)
          }
        })

      })

    }
    if(this.status == 'rejected'){
      return newPromise = new Promise((resolve,reject)=>{
        setTimeout(()=>{
          try{
            let x = onRejected(this.reason)
            this.resolvePromise(newPromise, x, resolve, reject);
          }catch (e){
            reject(e)
          }
        })

      })

    }
    if(this.status == 'padding'){
      return newPromise = new Promise((resolve,reject)=> {
        /*3.當(dāng)excutor為異步的時(shí)候先把then方法里面的回調(diào)儲存在失敗或者成功的隊(duì)列里面*/
       // 一個(gè)promise可以then多次 ，等會改變狀態(tài)后會讓then中的函數(shù)執(zhí)行
       // promise.then((data)=>{
       //    console.log('res',data);
      // },(err)=>{ 
      //     console.log(err);
     // });
     // promise.then((data)=>{
     //    console.log('res',data);
     //},(err)=>{ 
     //    console.log(err);
    //});
        this.onFulfilledCallback.push(() => {
          //這里可以寫其他的代碼對resolve做一層封裝todo
          setTimeout(()=> {
            try {
              let x = onFulfilled(this.value)
              this.resolvePromise(newPromise, x, resolve, reject);
            } catch (e) {
              reject(e)
            }
          })
        })
        this.onRejectedCallback.push(() => {
          setTimeout(()=> {
            try {
              let x = onRejected(this.reason)
              this.resolvePromise(newPromise, x, resolve, reject);
            } catch (e) {
              reject(e)
            }
          })
        })
      })
    }
    //4.保證鏈?zhǔn)秸{(diào)用 返回this  這樣做雖然能鏈?zhǔn)秸{(diào)用但是 所有鏈?zhǔn)秸{(diào)用的回調(diào)函數(shù)都掛載到同一個(gè)對象上 且當(dāng)后面的then方法執(zhí)行
    //的時(shí)候promise的狀態(tài)已經(jīng)確定會馬上執(zhí)行其對應(yīng)的回調(diào)，并且參數(shù)都為this.value這一個(gè)值
    //return this
  }
  catch(onRejected){
    this.then(null,onRejected)
  }
  resolvePromise(newPromise,x,resolve,reject){
    //2.3.1規(guī)范，避免循環(huán)引用
    if (newPromise === x) {
      return reject(new TypeError('Circular reference'));
    }
    //called變量主要是用來判斷如果resolvePromise函數(shù)已經(jīng)resolve或者reject了，那就不需要在執(zhí)行下面的resolce或者reject。
    //設(shè)置一個(gè)標(biāo)志位，在執(zhí)行resolve或者reject其中之一后，講不能再執(zhí)行resolve或者reject  eg:resolve();reject()
    let called = false;
    if (x != null && ((typeof x === 'object') || (typeof x === 'function'))) {
      try{
        let then = x.then;
        if (typeof then === 'function') {
          //2.3.3.3 如果 then 是一個(gè)函數(shù)，以x為this調(diào)用then函數(shù)，且第一個(gè)參數(shù)是resolve，第二個(gè)參數(shù)是reject
          then.call(x, y => {
            if (called) return;
            called = true;
            this.resolvePromise(newPromise, y, resolve, reject);
          }, error => {
            if (called) return;
            called = true;
            reject(error);
          })
        } else {
          //2.3.3.4 如果 then不是一個(gè)函數(shù)，則 以x為值fulfill promise。
          resolve(x);
        }
      }catch(e){
        if (called) return;
        called = true;
        reject(e);
      }

    }else {
      resolve(x)
    }
  }

}
// 執(zhí)行測試用例需要用到的代碼
Promise.deferred = function() {
  let defer = {};
  defer.promise = new Promise((resolve, reject) => {
    defer.resolve = resolve;
    defer.reject = reject;
  });
  return defer;
}
try {
  module.exports = Promise
} catch (e) {}

// 1.npm i -g promises-aplus-tests
// 2.promises-aplus-tests mypromise.js