'use strict';

var PENDING = 'pending';
var SETTLED = 'settled';
var FULFILLED = 'fulfilled';
var REJECTED = 'rejected';
var NOOP = function () {};

// async calls
var asyncSetTimer = typeof setImmediate !== 'undefined' ? setImmediate : setTimeout;
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')) {
			var then = value.then; // then should be retrived only once

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

						if (value !== val) {
							resolve(promise, val);
						} else {
							fulfill(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);
}

/**
 * @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,

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

		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;
