function resolve_promise_value(promise,value) {//PromiseA+的實現
    var then;
    /*
        ret false 說明沒有執行promise._resolve裡的函式
        ret true 說明執行了promise._resolve裡的函式
        ret error 說明執行promise._resolve裡的函式過程中出現錯誤
    */
    var ret = false;

    /*
        resolve(promise)和執行resolve狀態時的回撥函式後返回的結果都需要執行resolve(promise,value)
    */
 

    if (value === promise) {//傳進來的物件不能等於當前的Promise物件
        promise.reject(new TypeError('TypeError'));
    } else if (value && value instanceof Promise){//回撥返回的值或者resolve的值是Promise物件時需要等待該Promise物件的狀態變更
        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');//設定當前Promise狀態的狀態和值
            promise.value = value;
            var error;
            while (fn = promise._resolve.shift()) {//執行resolve回撥佇列裡的函式
                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式的異常資訊
                }
            }
        }
    }  else {
        ret = true;
        var fn;
        promise.setState('fulfilled');//設定當前Promise狀態的狀態和值
        promise.value = value;
        var error;
        while (fn = promise._resolve.shift()) {//執行resolve回撥佇列裡的函式
            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) {//判斷物件型別函式
    return  Object.prototype.toString.call(arg).match(/ (\w+)/)[1];
}

function Promise(fn,value,state) {
    if (!(this instanceof Promise)) {//防止不用new呼叫Promise函式
        return new Promise(fn);
    }
    this._resolve = [];//Promise物件的fulfilled時執行的回撥佇列
    this._reject = [];//Promise物件的rejected時執行的回撥佇列
    this.next = null;//執行下一個Promise物件
    this.value = value || null;//當前Promise物件的值
    this.state = state || 'pending';//當前Promise物件的狀態
    this.id = Promise.idFactory();
    /*
        new 的時候如果有函式，就執行該函式，把resolve和reject函式作為引數傳進去，並且繫結對應的Promise物件
    */
    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物件是否相等
        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) {//設定Promise物件的狀態
        this.state = state;
    },
    reject: function(value) {
        if (this.state === 'pending') {
            setTimeout((function() {
                this.setState('rejected');//設定Promise物件狀態
                this.value = value;//記錄Promise物件對應的值
                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回撥函式
                    try {
                        if (typeof fn == 'function') {//對於回撥函式佇列，只需記錄最後一個函式的執行結果
                            var result = fn(value);
                            this.value = result;
                        } 
                    } catch (err) {//捕獲異常，保證回撥佇列裡的函式每一個都被執行
                        error || (error = err);
                    }
                }
                if (this.next) {
                    if (error) {
                        this.next.reject(error);
                    } 
                    /*
                        執行完當前Promise物件的回撥後，如果Promise鏈上有下一個Promise物件，繼續執行，當前的Promise物件的值傳進去
                        如果error為true則說明上面程式碼執行中有異常，把異常物件傳給下一個Promise物件
                    */
                    else {
                        resolve_promise_value(this.next,result);
                    }
                }
            }).bind(this),0)

        }
    },
    then: function(resolve,reject) {//增加resolve和reject回撥
        if (this.state != 'pending') {//如果當前Promise物件已經resolve或reject則根據當前Promise物件狀態非同步執行傳進來的resolve或reject函式
            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回撥
        (type(reject) === 'Function') && this._reject.push(reject);
        this.next = new Promise();//返回一個新的Promise物件
        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') {//引數需要Promise陣列
        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物件
    for (var i = 0; i< promiseArr.length ;i++) {
        promiseArr[i].then((function(i) {//每個Promise fulfilled後記錄結果並且判斷是否全部Promise物件已經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物件reject並且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物件resolve的話就返回，並且放棄其餘的Promise物件的結果
                ret.resolve(value);
            }
        },function(value) {
            if (ret.state === 'pending') {//有一個Promise物件reject的話就返回，並且放棄其餘的Promise物件的結果
                ret.reject(value);
            }    
        });
    }
    return ret;
}

Promise.resolve = function(arg) {
    if (arg && arg instanceof Promise) {//引數是Promise物件的話直接返回
        return arg;
    } else {//否則用引數構造一個Promise物件
        var result = new Promise((arg && arg.then) || null,(arg && arg.then) ? null : arg,'fulfilled');
        //result.resolve(arg);
        return result;
    }
}

Promise.reject = function(arg) {//同resolve
    if (arg && arg instanceof Promise) {
        return arg;
    } else {
        var result = new Promise((arg && arg.then) || null,(arg && arg.then) ? null : arg,'reject');
        //result.reject(arg);
        return result;
    }
}
Promise.idFactory = (function() {//id構造工廠，id用於比較是否是同一個Promise物件
    var _id = 0;
    return function() {
        return _id += 1;
    }
})();

module.exports = Promise;