摘要：的實現說明沒有執行里的函數說明執行了里的函數說明執行里的函數過程中出現錯誤和執行狀態時的回調函數后返回的結果都需要執行傳進來的對象不能等于當前的對象回調返回的值或者的值是對象時需要等待該對象的狀態變更設置當前狀態的狀態和值執行回調隊列里的函

function resolve_promise_value(promise,value) {//PromiseA+的實現
    var then;
    /*
        ret false 說明沒有執行promise._resolve里的函數
        ret true 說明執行了promise._resolve里的函數
        ret error 說明執行promise._resolve里的函數過程中出現錯誤
    */
    var ret = false;
    
    /*
        resolve(promise)和執行resolve狀態時的回調函數后返回的結果都需要執行resolve(promise,value)
    */
    if (value === promise) {//傳進來的對象不能等于當前的Promise對象
        promise.reject(new TypeError("TypeError"));
    } else if (value && value instanceof Promise){//回調返回的值或者resolve的值是Promise對象時需要等待該Promise對象的狀態變更
        value.then(promise.resolve.bind(promise),promise.reject.bind(promise));
    } else if (type(value) === "Object" || type(value) === "Function") {
        try {
            then = value.then;
        } catch(getThenErr) {
            promise.reject(thenErr);
        }
        if (type(then) === "Function") {
            try {
                then.call(value,promise.resolve.bind(promise),promise.reject.bind(promise));
            } catch(callThenErr) {
                if (promise.state === "pending") {
                    promise.reject(callThenErr);
                } 
            }
        } else {
            ret = true;
            var fn;
            promise.setState("fulfilled");//設置當前Promise狀態的狀態和值
            promise.value = value;
            var error;
            while (fn = promise._resolve.shift()) {//執行resolve回調隊列里的函數
                try {
                    if (typeof fn == "function") {
                        var result = fn(value);
                        promise.value = result;
                    } 
                } catch (err) {
                    ret || (ret = err);//記錄第一個執行出錯的函數的異常信息
                }
            }
        }
    }  else {
        ret = true;
        var fn;
        promise.setState("fulfilled");//設置當前Promise狀態的狀態和值
        promise.value = value;
        var error;
        while (fn = promise._resolve.shift()) {//執行resolve回調隊列里的函數
            try {
                if (typeof fn == "function") {
                    var result = fn(value);
                    promise.value = result;
                } 
            } catch (err) {
                (ret instanceof Error) || (ret = err);
            }
        }
    }

    if (promise.next) {
        if (ret === true) {
            resolve_promise_value(promise.next,promise.value);
        }
        else if (ret instanceof Error){
            promise.next.reject(ret);    
        }
    }
    
}

function type(arg) {//判斷對象類型函數
    return  Object.prototype.toString.call(arg).match(/ (w+)/)[1];
}

function Promise(fn,value,state) {
    if (!(this instanceof Promise)) {//防止不用new調用Promise函數
        return new Promise(fn);
    }
    this._resolve = [];//Promise對象的fulfilled時執行的回調隊列
    this._reject = [];//Promise對象的rejected時執行的回調隊列
    this.next = null;//執行下一個Promise對象
    this.value = value || null;//當前Promise對象的值
    this.state = state || "pending";//當前Promise對象的狀態
    this.id = Promise.idFactory();
    /*
        new 的時候如果有函數，就執行該函數，把resolve和reject函數作為參數傳進去，并且綁定對應的Promise對象
    */
    try {
      fn && fn(this.resolve.bind(this),this.reject.bind(this));
    } catch (e) {
      this.reject(e);
    }
}

Promise.prototype = {
    equal: function(promise) {//根據id判斷兩個Promise對象是否相等
        return promise && (type(promise.then) === "Function") && (this.id === promise.id);
    },
    resolve: function(value) {
        if(this.state !== "pending"){
            return;
        }
        setTimeout((function() {
            resolve_promise_value(this,value)
        }).bind(this),0);
        
    },
    setState: function(state) {//設置Promise對象的狀態
        this.state = state;
    },
    reject: function(value) {
        if (this.state === "pending") {
            setTimeout((function() {
                this.setState("rejected");//設置Promise對象狀態
                this.value = value;//記錄Promise對象對應的值
                var fn;
                var error;
                if (this._reject.length === 0) {
                    if (this.next) {
                        this.next.reject(value);
                    }
                    return;
                }
                while (fn = this._reject.shift()) {//執行reject回調函數
                    try {
                        if (typeof fn == "function") {//對于回調函數隊列，只需記錄最后一個函數的執行結果
                            var result = fn(value);
                            this.value = result;
                        } 
                    } catch (err) {//捕獲異常，保證回調隊列里的函數每一個都被執行
                        error || (error = err);
                    }
                }
                if (this.next) {
                    if (error) {
                        this.next.reject(error);
                    } 
                    /*
                        執行完當前Promise對象的回調后，如果Promise鏈上有下一個Promise對象，繼續執行，當前的Promise對象的值傳進去
                        如果error為true則說明上面代碼執行中有異常，把異常對象傳給下一個Promise對象
                    */
                    else {
                        resolve_promise_value(this.next,result);
                    }
                }
            }).bind(this),0)
            
        }
    },
    then: function(resolve,reject) {//增加resolve和reject回調
        if (this.state != "pending") {//如果當前Promise對象已經resolve或reject則根據當前Promise對象狀態異步執行傳進來的resolve或reject函數
            this.state === "fulfilled" ? (resolve = resolve || function() {}) : (reject = reject || function() {});
            setTimeout(this.state === "fulfilled" ? resolve.bind(null,this.value) : reject.bind(null,this.value),0);
            return;
        }
        (type(resolve) === "Function") && this._resolve.push(resolve);//記錄resolve回調
        (type(reject) === "Function") && this._reject.push(reject);
        this.next = new Promise();//返回一個新的Promise對象
        return this.next;
    },
    catch: function(reject) {//then(undefined,callback)的語法糖
        return this.then(void 0,reject);
    }
}
Promise.all = function(promiseArr) {
    if (type(promiseArr) !== "Array") {//參數需要Promise數組
        new Error("need a Array");
    }
    var count = 0;
    var result = [];//記錄每個Promise的結果
    var ret = new Promise();//返回新的Promose對象
    for (var i = 0; i< promiseArr.length ;i++) {
        promiseArr[i].then((function(i) {//每個Promise fulfilled后記錄結果并且判斷是否全部Promise對象已經fulfilled
            return function(value) {
                result[i] = value;
                count++;
                if (count === promiseArr.length) {//全部Promise fulfilled的話就執行resovle
                    ret.resolve(result); 
                }
            }
        })(i),function(value) {
            if (ret.state === "pending") {//有一個Promise對象reject并且ret還是pending狀態的話就直接返回
                ret.reject(value);
            }    
        })
    }
    return ret;
}

Promise.race = function(promiseArr) {
    if (type(promiseArr) !== "Array") {
        new Error("need a Array");
    }
    var ret = new Promise();
    for (var i = 0; i< promiseArr.length ;i++) {
        promiseArr[i].then(function(value) {
            if (ret.state === "pending") {//有一個Promise對象resolve的話就返回，并且放棄其余的Promise對象的結果
                ret.resolve(value);
            }
        },function(value) {
            if (ret.state === "pending") {//有一個Promise對象reject的話就返回，并且放棄其余的Promise對象的結果
                ret.reject(value);
            }    
        });
    }
    return ret;
}

Promise.resolve = function(arg) {
    if (arg && typeof arg.then === "function") {//參數是Promise對象的話直接返回
        return arg;
    } else {//否則用參數構造一個Promise對象
        var result = new Promise(null,arg,"fulfilled");
        //result.resolve(arg);
        return result;
    }
}

Promise.reject = function(arg) {//同resolve
    if (arg && typeof arg.then === "function") {
        return arg;
    } else {
        var result = new Promise(null,arg,"reject");
        //result.reject(arg);
        return result;
    }
}
Promise.idFactory = (function() {//id構造工廠，id用于比較是否是同一個Promise對象
    var _id = 0;
    return function() {
        return _id += 1;
    }
})();

module.exports = Promise;