摘要：緩存默認狀態為此變量里放著此的結果存放的著所有成功的回調函數存放著所有的失敗的回調函數調用此方法可以把變成成功態的時候你把掙到的錢傳進來調用此方法可以把當前的變成失敗態如果當前狀態是初始態，則轉成失敗態立即執行傳入的任務如果就是循環引用成功

function Promise(task) {
    let that = this;//緩存this
    //默認狀態為pending
    that.status = "pending";
    //此變量里放著此promise的結果
    that.value = undefined;
    //存放的著所有成功的回調函數
    that.onResolvedCallbacks = [];
    //存放著所有的失敗的回調函數
    that.onRejectedCallbacks = [];
    //調用此方法可以把promise變成成功態
    //resolve的時候你把掙到的錢傳進來
    function resolve(value) {
        if(value instanceof Promise){
            return value.then(resolve,reject);
        }
        if (that.status == "pending") {
            that.status = "fulfilled";
            that.value = value;
            that.onResolvedCallbacks.forEach(item=>item(that.value));
        }
    }

    //調用此方法可以把當前的promise變成失敗態
    function reject(reason) {
        //如果當前狀態是初始態，則轉成失敗態
        if (that.status == "pending") {
            that.status = "rejected";
            that.value = reason;
            that.onRejectedCallbacks.forEach(item=>item(that.value));
        }
    }

    //立即執行傳入的任務
    try {
        task(resolve, reject);
    } catch (e) {
        reject(e);
    }
}
function resolvePromise(promise2,x,resolve,reject){
    let then;
    //如果x就是promise2
    if(promise2 === x){
        return reject(new TypeError("循環引用"));
    }
    if(x instanceof Promise){
        if(x.status == "pending"){
            x.then(function(y){
                resolvePromise(promise2,y,resolve,reject);
            },reject);
        }else if(x.status == "fulfilled"){
            resolve(x.value);
        }else if(x.status == "rejected"){
            reject(x.value);
        }
    }else if(x!=null && (typeof x == "object" || typeof x == "function")){
        try{
            then = x.then;
            if(typeof then == "function"){
                then.call(x,function(y){
                    resolvePromise(promise2,y,resolve,reject)
                },reject);
            }
        }catch(e){
            reject(e);
        };
    }else{
        resolve(x);
    }
}
//onFulfilled成功的回調，onReject失敗的回調
Promise.prototype.then = function (onFulfilled, onReject) {
    onFulfilled = typeof onFulfilled == "function"?onFulfilled:function(value){return value};
    onReject = typeof onReject=="function"?onReject:function(reason){
        throw reason;
    }
    let that = this;
    let promise2;
    if(that.status == "fulfilled"){
        promise2 = new Promise(function(resolve,reject){
            let x = onFulfilled(that.value);
            resolvePromise(promise2,x,resolve,reject);
        });
    }
    if(that.status == "rejected"){
        promise2 = new Promise(function(resolve,reject){
            let x = onReject(that.value);
            resolvePromise(promise2,x,resolve,reject);
        });

    }
    if(that.status == "pending"){
        promise2 = new Promise(function(resolve,reject){
            that.onResolvedCallbacks.push(function(){
                let x = onFulfilled(that.value);
                resolvePromise(promise2,x,resolve,reject);
            });
            that.onRejectedCallbacks.push(function(){
                let x = onReject(that.value);
                resolvePromise(promise2,x,resolve,reject);
            });
        });
    }
    return promise2;
}

Promise.all = function (arr) {
    return new Promise((resolve,reject) =>{
        let values = []
        let len = arr.length
        for(var i = 0;i < len; i++){
            let promise = arr[i]
            if(typeof promise.then == "function"){
                promise.then(res=>{
                    values.push(res)
                    if(values.length == len){
                        resolve(values)
                    }
                })
            }
        }
    })
}

Promise.race = function (arr) {
    return new Promise((resolve,reject) =>{
        let len = arr.length
        for(var i = 0;i < len; i++){
            let promise = arr[i]
            if(typeof promise.then == "function"){
                promise.then(res=>{
                    resolve(res)
                })
            }
        }
    })
}

Promise.resolve = function (value) {
    if (value instanceof Promise) return value
    return new Promise(resolve => resolve(value))
}

Promise.reject = function (value) {
    return new Promise((resolve,reject)=>reject(value))
}


module.exports = Promise;