'use strict';

var PENDING = 'pending'; var SETTLED = 'settled'; var FULFILLED = 'fulfilled'; var REJECTED = 'rejected'; var NOOP = function () {}; var isNode = typeof global !== 'undefined' && typeof global.process !== 'undefined' && typeof global.process.emit === 'function';

var asyncSetTimer = typeof setImmediate === 'undefined' ? setTimeout : setImmediate; var asyncQueue = []; var asyncTimer;

function asyncFlush() {

// run promise callbacks
for (var i = 0; i < asyncQueue.length; i++) {
        asyncQueue[i][0](asyncQueue[i][1]);
}

// reset async asyncQueue
asyncQueue = [];
asyncTimer = false;

}

function asyncCall(callback, arg) {

asyncQueue.push([callback, arg]);

if (!asyncTimer) {
        asyncTimer = true;
        asyncSetTimer(asyncFlush, 0);
}

}

function invokeResolver(resolver, promise) {

function resolvePromise(value) {
        resolve(promise, value);
}

function rejectPromise(reason) {
        reject(promise, reason);
}

try {
        resolver(resolvePromise, rejectPromise);
} catch (e) {
        rejectPromise(e);
}

}

function invokeCallback(subscriber) {

var owner = subscriber.owner;
var settled = owner._state;
var value = owner._data;
var callback = subscriber[settled];
var promise = subscriber.then;

if (typeof callback === 'function') {
        settled = FULFILLED;
        try {
                value = callback(value);
        } catch (e) {
                reject(promise, e);
        }
}

if (!handleThenable(promise, value)) {
        if (settled === FULFILLED) {
                resolve(promise, value);
        }

        if (settled === REJECTED) {
                reject(promise, value);
        }
}

}

function handleThenable(promise, value) {

var resolved;

try {
        if (promise === value) {
                throw new TypeError('A promises callback cannot return that same promise.');
        }

        if (value && (typeof value === 'function' || typeof value === 'object')) {
                // then should be retrieved only once
                var then = value.then;

                if (typeof then === 'function') {
                        then.call(value, function (val) {
                                if (!resolved) {
                                        resolved = true;

                                        if (value === val) {
                                                fulfill(promise, val);
                                        } else {
                                                resolve(promise, val);
                                        }
                                }
                        }, function (reason) {
                                if (!resolved) {
                                        resolved = true;

                                        reject(promise, reason);
                                }
                        });

                        return true;
                }
        }
} catch (e) {
        if (!resolved) {
                reject(promise, e);
        }

        return true;
}

return false;

}

function resolve(promise, value) {

if (promise === value || !handleThenable(promise, value)) {
        fulfill(promise, value);
}

}

function fulfill(promise, value) {

if (promise._state === PENDING) {
        promise._state = SETTLED;
        promise._data = value;

        asyncCall(publishFulfillment, promise);
}

}

function reject(promise, reason) {

if (promise._state === PENDING) {
        promise._state = SETTLED;
        promise._data = reason;

        asyncCall(publishRejection, promise);
}

}

function publish(promise) {

promise._then = promise._then.forEach(invokeCallback);

}

function publishFulfillment(promise) {

promise._state = FULFILLED;
publish(promise);

}

function publishRejection(promise) {

promise._state = REJECTED;
publish(promise);
if (!promise._handled && isNode) {
        global.process.emit('unhandledRejection', promise._data, promise);
}

}

function notifyRejectionHandled(promise) {

global.process.emit('rejectionHandled', promise);

}

/**

* @class
*/

function Promise(resolver) {

if (typeof resolver !== 'function') {
        throw new TypeError('Promise resolver ' + resolver + ' is not a function');
}

if (this instanceof Promise === false) {
        throw new TypeError('Failed to construct \'Promise\': Please use the \'new\' operator, this object constructor cannot be called as a function.');
}

this._then = [];

invokeResolver(resolver, this);

}

Promise.prototype = {

constructor: Promise,

_state: PENDING,
_then: null,
_data: undefined,
_handled: false,

then: function (onFulfillment, onRejection) {
        var subscriber = {
                owner: this,
                then: new this.constructor(NOOP),
                fulfilled: onFulfillment,
                rejected: onRejection
        };

        if ((onRejection || onFulfillment) && !this._handled) {
                this._handled = true;
                if (this._state === REJECTED && isNode) {
                        asyncCall(notifyRejectionHandled, this);
                }
        }

        if (this._state === FULFILLED || this._state === REJECTED) {
                // already resolved, call callback async
                asyncCall(invokeCallback, subscriber);
        } else {
                // subscribe
                this._then.push(subscriber);
        }

        return subscriber.then;
},

catch: function (onRejection) {
        return this.then(null, onRejection);
}

};

Promise.all = function (promises) {

if (!Array.isArray(promises)) {
        throw new TypeError('You must pass an array to Promise.all().');
}

return new Promise(function (resolve, reject) {
        var results = [];
        var remaining = 0;

        function resolver(index) {
                remaining++;
                return function (value) {
                        results[index] = value;
                        if (!--remaining) {
                                resolve(results);
                        }
                };
        }

        for (var i = 0, promise; i < promises.length; i++) {
                promise = promises[i];

                if (promise && typeof promise.then === 'function') {
                        promise.then(resolver(i), reject);
                } else {
                        results[i] = promise;
                }
        }

        if (!remaining) {
                resolve(results);
        }
});

};

Promise.race = function (promises) {

if (!Array.isArray(promises)) {
        throw new TypeError('You must pass an array to Promise.race().');
}

return new Promise(function (resolve, reject) {
        for (var i = 0, promise; i < promises.length; i++) {
                promise = promises[i];

                if (promise && typeof promise.then === 'function') {
                        promise.then(resolve, reject);
                } else {
                        resolve(promise);
                }
        }
});

};

Promise.resolve = function (value) {

if (value && typeof value === 'object' && value.constructor === Promise) {
        return value;
}

return new Promise(function (resolve) {
        resolve(value);
});

};

Promise.reject = function (reason) {

return new Promise(function (resolve, reject) {
        reject(reason);
});

};

module.exports = Promise;