const PENDING = "pending";
const RESOLVED = "resolved";
const REJECTED = "rejected";
function MyPromise(fn) {
  // 保存初始化狀態(tài)
  var self = this;
  // 初始化狀態(tài)
  this.state = PENDING;
  // 用于保存 resolve 或者 rejected 傳入的值
  this.value = null;
  // 用于保存 resolve 的回調(diào)函數(shù)
  this.resolvedCallbacks = [];
  // 用于保存 reject 的回調(diào)函數(shù)
  this.rejectedCallbacks = [];
  // 狀態(tài)轉(zhuǎn)變?yōu)?resolved 方法
  function resolve(value) {
    // 判斷傳入元素是否為 Promise 值，如果是，則狀態(tài)改變必須等待前一個(gè)狀態(tài)改變后再進(jìn)行改變
    if (value instanceof MyPromise) {
      return value.then(resolve, reject);
    }
    // 保證代碼的執(zhí)行順序?yàn)楸据喪录h(huán)的末尾
    setTimeout(() => {
      // 只有狀態(tài)為 pending 時(shí)才能轉(zhuǎn)變，
      if (self.state === PENDING) {
        // 修改狀態(tài)
        self.state = RESOLVED;
        // 設(shè)置傳入的值
        self.value = value;
        // 執(zhí)行回調(diào)函數(shù)
        self.resolvedCallbacks.forEach(callback => {
          callback(value);
        });
      }
    }, 0);
  }
  // 狀態(tài)轉(zhuǎn)變?yōu)?rejected 方法
  function reject(value) {
    // 保證代碼的執(zhí)行順序?yàn)楸据喪录h(huán)的末尾
    setTimeout(() => {
      // 只有狀態(tài)為 pending 時(shí)才能轉(zhuǎn)變
      if (self.state === PENDING) {
        // 修改狀態(tài)
        self.state = REJECTED;
        // 設(shè)置傳入的值
        self.value = value;
        // 執(zhí)行回調(diào)函數(shù)
        self.rejectedCallbacks.forEach(callback => {
          callback(value);
        });
      }
    }, 0);
  }
  // 將兩個(gè)方法傳入函數(shù)執(zhí)行
  try {
    fn(resolve, reject);
  } catch (e) {
    // 遇到錯(cuò)誤時(shí)，捕獲錯(cuò)誤，執(zhí)行 reject 函數(shù)
    reject(e);
  }
}
MyPromise.prototype.then = function(onResolved, onRejected) {
  // 首先判斷兩個(gè)參數(shù)是否為函數(shù)類型，因?yàn)檫@兩個(gè)參數(shù)是可選參數(shù)
  onResolved =
    typeof onResolved === "function"
      ? onResolved
      : function(value) {
          return value;
        };
  onRejected =
    typeof onRejected === "function"
      ? onRejected
      : function(error) {
          throw error;
        };
  // 如果是等待狀態(tài)，則將函數(shù)加入對應(yīng)列表中
  if (this.state === PENDING) {
    this.resolvedCallbacks.push(onResolved);
    this.rejectedCallbacks.push(onRejected);
  }
  // 如果狀態(tài)已經(jīng)凝固，則直接執(zhí)行對應(yīng)狀態(tài)的函數(shù)
  if (this.state === RESOLVED) {
    onResolved(this.value);
  }
  if (this.state === REJECTED) {
    onRejected(this.value);
  }
};

then(onFulfilled, onReject){
    // 保存前一個(gè)promise的this
    const self = this; 
    return new MyPromise((resolve, reject) => {
      // 封裝前一個(gè)promise成功時(shí)執(zhí)行的函數(shù)
      let fulfilled = () => {
        try{
          const result = onFulfilled(self.value); // 承前
          return result instanceof MyPromise? result.then(resolve, reject) : resolve(result); //啟后
        }catch(err){
          reject(err)
        }
      }
      // 封裝前一個(gè)promise失敗時(shí)執(zhí)行的函數(shù)
      let rejected = () => {
        try{
          const result = onReject(self.reason);
          return result instanceof MyPromise? result.then(resolve, reject) : reject(result);
        }catch(err){
          reject(err)
        }
      }
      switch(self.status){
        case PENDING: 
          self.onFulfilledCallbacks.push(fulfilled);
          self.onRejectedCallbacks.push(rejected);
          break;
        case FULFILLED:
          fulfilled();
          break;
        case REJECT:
          rejected();
          break;
      }
    })
   }

function promiseAll(promises) {
  return new Promise(function(resolve, reject) {
    if(!Array.isArray(promises)){
        throw new TypeError(`argument must be a array`)
    }
    var resolvedCounter = 0;
    var promiseNum = promises.length;
    var resolvedResult = [];
    for (let i = 0; i < promiseNum; i++) {
      Promise.resolve(promises[i]).then(value=>{
        resolvedCounter++;
        resolvedResult[i] = value;
        if (resolvedCounter == promiseNum) {
            return resolve(resolvedResult)
          }
      },error=>{
        return reject(error)
      })
    }
  })
}
// test
let p1 = new Promise(function (resolve, reject) {
    setTimeout(function () {
        resolve(1)
    }, 1000)
})
let p2 = new Promise(function (resolve, reject) {
    setTimeout(function () {
        resolve(2)
    }, 2000)
})
let p3 = new Promise(function (resolve, reject) {
    setTimeout(function () {
        resolve(3)
    }, 3000)
})
promiseAll([p3, p1, p2]).then(res => {
    console.log(res) // [3, 1, 2]
})

Promise.race = function (args) {
  return new Promise((resolve, reject) => {
    for (let i = 0, len = args.length; i < len; i++) {
      args[i].then(resolve, reject)
    }
  })
}