const PENDING = 'PENDING';
const FULFILLED = 'FULFILLED';
const REJECTED = 'REJECTED';


// 利用x的值來判斷是調(diào)用promise2的resolve還是reject
function resolvePromise(promise2, x, resolve, reject) {
    // 核心流程
    if (promise2 === x) {
        return reject(new TypeError('錯(cuò)誤'))
    }
    // 我可能寫的promise 要和別人的promise兼容信柿，考慮不是自己寫的promise情況
    if ((typeof x === 'object' && x !== null) || typeof x === 'function') { // 有可能是promise 
        // 別人的promise可能調(diào)用成功后 還能調(diào)用失敗~~~  確保了別人promise符合規(guī)范
        let called = false;
        try { // 有可能then方法是通過defineProperty來實(shí)現(xiàn)的 取值時(shí)可能會(huì)發(fā)生異常
            let then = x.then;
            if (typeof then === 'function') {
                // 這里我就認(rèn)為你是promise了  x.then 這樣寫會(huì)觸發(fā)getter可能會(huì)發(fā)生異常  
                then.call(x, y => {
                    if (called) return;
                    called = true;
                    resolvePromise(promise2, y, resolve, reject); // 直到解析他不是promise位置
                }, r => { // reason
                    if (called) return;
                    called = true;
                    reject(r);
                });
            } else { // {}  {then:{}}
                resolve(x); // 常量
            }
        } catch (e) {
            if (called) return;
            called = true;
            reject(e);
        }
    } else {
        resolve(x); // 說明返回的是一個(gè)普通值 直接將他放到promise2.resolve中
    }
}

class Promise {
    constructor(executor) {
        this.status = PENDING; // promise默認(rèn)的狀態(tài)
        this.value = undefined; // 成功的原因
        this.reason = undefined; // 失敗的原因
        this.onResolvedCallbacks = []; // 存放成功的回調(diào)方法
        this.onRejectedCallbacks = []; // 存放失敗的回調(diào)方法
        const resolve = (value) => { // 成功resolve函數(shù)
            if(value instanceof Promise){
                return value.then(resolve,reject)
            }
            if (this.status === PENDING) {
                this.value = value;
                this.status = FULFILLED; // 修改狀態(tài)
                // 發(fā)布
                this.onResolvedCallbacks.forEach(fn => fn());
            }
        }
        const reject = (reason) => { // 失敗的reject函數(shù)
            if (this.status === PENDING) {
                this.reason = reason;
                this.status = REJECTED // 修改狀態(tài)
                this.onRejectedCallbacks.forEach(fn => fn());
            }
        }
        try {
            executor(resolve, reject);
        } catch (e) {
            reject(e);
        }
    }
    // then中的參數(shù)是可選的
    then(onFulfilled, onRejected) { // onFulfilled, onRejected
        onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : v => v;
        onRejected = typeof onRejected === 'function' ? onRejected : err => { throw err; }
        // 用于實(shí)現(xiàn)鏈?zhǔn)秸{(diào)用
        let promise2 = new Promise((resolve, reject) => {
            // 訂閱模式
            if (this.status == FULFILLED) { // 成功調(diào)用成功方法
                setTimeout(() => {
                    try {
                        let x = onFulfilled(this.value);
                        // 此x 可能是一個(gè)promise殿雪， 如果是promise需要看一下這個(gè)promise是成功還是失敗 .then ,如果成功則把成功的結(jié)果 調(diào)用promise2的resolve傳遞進(jìn)去牲证，如果失敗則同理

                        // 總結(jié) x的值 決定是調(diào)用promise2的 resolve還是reject丢早，如果是promise則取他的狀態(tài)，如果是普通值則直接調(diào)用resolve
                        resolvePromise(promise2, x, resolve, reject);
                    } catch (e) {
                        reject(e);
                    }
                }, 0);
            }
            if (this.status === REJECTED) { // 失敗調(diào)用失敗方法
                setTimeout(() => {
                    try {
                        let x = onRejected(this.reason);
                        resolvePromise(promise2, x, resolve, reject);
                    } catch (e) {
                        reject(e);
                    }
                }, 0);

            }
            if (this.status == PENDING) { // 代碼是異步調(diào)用resolve或者reject的
                this.onResolvedCallbacks.push(() => { // 切片編程 AOP
                    setTimeout(() => {
                        try {
                            // todo...
                            let x = onFulfilled(this.value);
                            resolvePromise(promise2, x, resolve, reject);
                        } catch (e) {
                            reject(e);
                        }
                    }, 0);

                });
                this.onRejectedCallbacks.push(() => {
                    setTimeout(() => {
                        try {
                            // todo...
                            let x = onRejected(this.reason);
                            resolvePromise(promise2, x, resolve, reject);
                        } catch (e) {
                            reject(e);
                        }
                    }, 0);
                });
            }
        })
        return promise2
    }
    static resolve(value){
        return new Promise((resolve,reject)=>{
            resolve(value);
        })
    }
    static reject(value){
        return new Promise((resolve,reject)=>{
            reject(value);
        })
    }
    catch(errorFn){
        return this.then(null,errorFn)
    }

    static all = function(promises) {
        return new Promise((resolve, reject) => {
            let result = [];
            let times = 0;
            const processSuccess = (index,val)=>{
                result[index] = val;
                if(++times === promises.length){
                    resolve(result)
                }
            }
            for (let i = 0; i < promises.length; i++) { // 并發(fā) 多個(gè)請求一起執(zhí)行的
                let p = promises[i]
                if(p && typeof p.then === 'function'){
                    p.then((data)=>{
                        processSuccess(i,data)
                    },reject); // 如果其中某一個(gè)promise失敗了 直接執(zhí)行失敗即可
                }else{
                    processSuccess(i,p)
                }
            }
        });
    }
}
// npm install promises-aplus-tests -g


// 延遲對象 幫我們減少一次套用 ： 針對目前來說 應(yīng)用不是很廣泛
Promise.deferred = function () {
    let dfd = {};
    dfd.promise = new Promise((resolve,reject)=>{
        dfd.resolve= resolve;
        dfd.reject = reject;
    }); 
    return dfd;
}
module.exports = Promise