/**
+ * Base IO functionality. Provides basic XHR transport support.
+ * @module io
+ * @submodule io-base
+ */
+
+ /**
+ * The io class is a utility that brokers HTTP requests through a simplified
+ * interface. Specifically, it allows JavaScript to make HTTP requests to
+ * a resource without a page reload. The underlying transport for making
+ * same-domain requests is the XMLHttpRequest object. YUI.io can also use
+ * Flash, if specified as a transport, for cross-domain requests.
+ *
+ * @class io
+ */
+
+ /**
+ * @event io:start
+ * @description This event is fired by YUI.io when a transaction is initiated.
+ * @type Event Custom
+ */
+ var E_START = 'io:start',
+
+ /**
+ * @event io:complete
+ * @description This event is fired by YUI.io when a transaction is complete.
+ * Response status and data are accessible, if available.
+ * @type Event Custom
+ */
+ E_COMPLETE = 'io:complete',
+
+ /**
+ * @event io:success
+ * @description This event is fired by YUI.io when a transaction is complete, and
+ * the HTTP status resolves to HTTP2xx.
+ * @type Event Custom
+ */
+ E_SUCCESS = 'io:success',
+
+ /**
+ * @event io:failure
+ * @description This event is fired by YUI.io when a transaction is complete, and
+ * the HTTP status resolves to HTTP4xx, 5xx and above.
+ * @type Event Custom
+ */
+ E_FAILURE = 'io:failure',
+
+ /**
+ * @event io:end
+ * @description This event signifies the end of the transaction lifecycle. The
+ * transaction transport is destroyed.
+ * @type Event Custom
+ */
+ E_END = 'io:end',
+
+ //--------------------------------------
+ // Properties
+ //--------------------------------------
+ /**
+ * @description A transaction counter that increments for each transaction.
+ *
+ * @property transactionId
+ * @private
+ * @static
+ * @type int
+ */
+ transactionId = 0,
+
+ /**
+ * @description Object of default HTTP headers to be initialized and sent
+ * for all transactions.
+ *
+ * @property _headers
+ * @private
+ * @static
+ * @type object
+ */
+ _headers = {
+ 'X-Requested-With' : 'XMLHttpRequest'
+ },
+
+ /**
+ * @description Object that stores timeout values for any transaction with
+ * a defined "timeout" configuration property.
+ *
+ * @property _timeout
+ * @private
+ * @static
+ * @type object
+ */
+ _timeout = {},
+
+ // Window reference
+ w = Y.config.win;
+
+ //--------------------------------------
+ // Methods
+ //--------------------------------------
+ /**
+ * @description Method for requesting a transaction. _io() is implemented as
+ * yui.io(). Each transaction may include a configuration object. Its
+ * properties are:
+ *
+ * method: HTTP method verb (e.g., GET or POST). If this property is not
+ * not defined, the default value will be GET.
+ *
+ * data: This is the name-value string that will be sent as the transaction
+ * data. If the request is HTTP GET, the data become part of
+ * querystring. If HTTP POST, the data are sent in the message body.
+ *
+ * xdr: Defines the transport to be used for cross-domain requests. By
+ * setting this property, the transaction will use the specified
+ * transport instead of XMLHttpRequest. Currently, the only alternate
+ * transport supported is Flash (e.g., { xdr: 'flash' }).
+ *
+ * form: This is a defined object used to process HTML form as data. The
+ * properties are:
+ * {
+ * id: object, //HTML form object or id of HTML form
+ * useDisabled: boolean, //Allow disabled HTML form field values
+ * to be sent as part of the data.
+ * }
+ *
+ * on: This is a defined object used to create and handle specific
+ * events during a transaction lifecycle. These events will fire in
+ * addition to the global io events. The events are:
+ * start - This event is fired when a request is sent to a resource.
+ * complete - This event fires when the transaction is complete.
+ * success - This event fires when the response status resolves to
+ * HTTP 2xx.
+ * failure - This event fires when the response status resolves to
+ * HTTP 4xx, 5xx; and, for all transaction exceptions,
+ * including aborted transactions and transaction timeouts.
+ * end - This even is fired at the conclusion of the transaction
+ * lifecycle, after a success or failure resolution.
+ *
+ * The properties are:
+ * {
+ * start: function(id, args){},
+ * complete: function(id, responseobject, args){},
+ * success: function(id, responseobject, args){},
+ * failure: function(id, responseobject, args){},
+ * end: function(id, args){}
+ * }
+ * Each property can reference a function or be written as an
+ * inline function.
+ *
+ * context: Object reference for an event handler when it is implemented
+ * as a method of a base object. Defining "context" will preserve
+ * the proper reference of "this" used in the event handler.
+ * headers: This is a defined object of client headers, as many as.
+ * desired for the transaction. These headers are sentThe object
+ * pattern is:
+ * {
+ * header: value
+ * }
+ *
+ * timeout: This value, defined as milliseconds, is a time threshold for the
+ * transaction. When this threshold is reached, and the transaction's
+ * Complete event has not yet fired, the transaction will be aborted.
+ * arguments: Object, array, string, or number passed to all registered
+ * event handlers. This value is available as the second
+ * argument in the "start" and "abort" event handlers; and, it is
+ * the third argument in the "complete", "success", and "failure"
+ * event handlers.
+ *
+ * @method _io
+ * @private
+ * @static
+ * @param {string} uri - qualified path to transaction resource.
+ * @param {object} c - configuration object for the transaction.
+ * @param {number} i - transaction id, if already set by queue.
+ * @return object
+ */
+ function _io(uri, c, i) {
+ var f, o, m;
+ c = c || {};
+ o = _create(c.xdr || c.form, i);
+ m = c.method ? c.method.toUpperCase() : 'GET';
+
+ if (c.form) {
+ if (c.form.upload) {
+ return Y.io._upload(o, uri, c);
+ }
+ else {
+ f = Y.io._serialize(c.form, c.data);
+ if (m === 'POST') {
+ c.data = f;
+ _setHeader('Content-Type', 'application/x-www-form-urlencoded');
+ }
+ else if (m === 'GET') {
+ uri = _concat(uri, f);
+ }
+ }
+ }
+ else if (c.data && m === 'GET') {
+ uri = _concat(uri, c.data);
+ }
+
+ if (c.xdr) {
+ if (c.xdr.use === 'native' && window.XDomainRequest || c.xdr.use === 'flash') {
+ return Y.io.xdr(uri, o, c);
+ }
+ if (c.xdr.credentials) {
+ o.c.withCredentials = true;
+ }
+ }
+
+ o.c.onreadystatechange = function() { _readyState(o, c); };
+ try {
+ o.c.open(m, uri, true);
+ }
+ catch(e0){
+ if (c.xdr) {
+ // This exception is usually thrown by browsers
+ // that do not support native XDR transactions.
+ return _resend(o, uri, c);
+ }
+ }
+
+ if (c.data && m === 'POST') {
+ _setHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
+ }
+
+ _setHeaders(o.c, c.headers || {});
+ try {
+ // Using "null" will result in a POST request with
+ // no Content-Length defined.
+ o.c.send(c.data || '');
+ }
+ catch(e1) {
+ if (c.xdr) {
+ // This exception is usually thrown by browsers
+ // that do not support native XDR transactions.
+ return _resend(o, uri, c);
+ }
+ }
+
+ _ioStart(o.id, c);
+ // If config.timeout is defined, and the request is standard XHR,
+ // initialize timeout polling.
+ if (c.timeout) {
+ _startTimeout(o, c.timeout);
+ }
+
+ return {
+ id: o.id,
+ abort: function() {
+ return o.c ? _ioCancel(o, 'abort') : false;
+ },
+ isInProgress: function() {
+ return o.c ? o.c.readyState !== 4 && o.c.readyState !== 0 : false;
+ }
+ }
+ }
+
+ /**
+ * @description Method for creating and subscribing transaction events.
+ *
+ * @method _subscribe
+ * @private
+ * @static
+ * @param {string} e - event to be published
+ * @param {object} c - configuration data subset for event subscription.
+ *
+ * @return void
+ */
+ function _subscribe(e, c){
+ var evt = new Y.EventTarget().publish('transaction:' + e);
+ evt.subscribe(c.on[e], (c.context || Y), c.arguments);
+
+ return evt;
+ }
+
+ /**
+ * @description Fires event "io:start" and creates, fires a
+ * transaction-specific start event, if config.on.start is
+ * defined.
+ *
+ * @method _ioStart
+ * @private
+ * @static
+ * @param {number} id - transaction id
+ * @param {object} c - configuration object for the transaction.
+ *
+ * @return void
+ */
+ function _ioStart(id, c) {
+ var evt;
+ // Set default value of argument c, property "on" to Object if
+ // the property is null or undefined.
+ c.on = c.on || {};
+
+ Y.fire(E_START, id);
+ if (c.on.start) {
+ evt = _subscribe('start', c);
+ evt.fire(id);
+ }
+ }
+
+
+ /**
+ * @description Fires event "io:complete" and creates, fires a
+ * transaction-specific "complete" event, if config.on.complete is
+ * defined.
+ *
+ * @method _ioComplete
+ * @private
+ * @static
+ * @param {object} o - transaction object.
+ * @param {object} c - configuration object for the transaction.
+ *
+ * @return void
+ */
+ function _ioComplete(o, c) {
+ var evt,
+ r = o.status ? { status: 0, statusText: o.status } : o.c;
+ // Set default value of argument c, property "on" to Object if
+ // the property is null or undefined.
+ c.on = c.on || {};
+
+ Y.fire(E_COMPLETE, o.id, r);
+ if (c.on.complete) {
+ evt = _subscribe('complete', c);
+ evt.fire(o.id, r);
+ }
+ }
+
+ /**
+ * @description Fires event "io:success" and creates, fires a
+ * transaction-specific "success" event, if config.on.success is
+ * defined.
+ *
+ * @method _ioSuccess
+ * @private
+ * @static
+ * @param {object} o - transaction object.
+ * @param {object} c - configuration object for the transaction.
+ *
+ * @return void
+ */
+ function _ioSuccess(o, c) {
+ var evt;
+ // Set default value of argument c, property "on" to Object if
+ // the property is null or undefined.
+ c.on = c.on || {};
+
+ Y.fire(E_SUCCESS, o.id, o.c);
+ if (c.on.success) {
+ evt = _subscribe('success', c);
+ evt.fire(o.id, o.c);
+ }
+
+ _ioEnd(o, c);
+ }
+
+ /**
+ * @description Fires event "io:failure" and creates, fires a
+ * transaction-specific "failure" event, if config.on.failure is
+ * defined.
+ *
+ * @method _ioFailure
+ * @private
+ * @static
+ * @param {object} o - transaction object.
+ * @param {object} c - configuration object for the transaction.
+ *
+ * @return void
+ */
+ function _ioFailure(o, c) {
+ var evt,
+ r = o.status ? { status: 0, statusText: o.status } : o.c;
+ // Set default value of argument c, property "on" to Object if
+ // the property is null or undefined.
+ c.on = c.on || {};
+
+ Y.fire(E_FAILURE, o.id, r);
+ if (c.on.failure) {
+ evt = _subscribe('failure', c);
+ evt.fire(o.id, r);
+ }
+
+ _ioEnd(o, c);
+ }
+
+ /**
+ * @description Fires event "io:end" and creates, fires a
+ * transaction-specific "end" event, if config.on.end is
+ * defined.
+ *
+ * @method _ioEnd
+ * @private
+ * @static
+ * @param {object} o - transaction object.
+ * @param {object} c - configuration object for the transaction.
+ *
+ * @return void
+ */
+ function _ioEnd(o, c) {
+ var evt;
+ // Set default value of argument c, property "on" to Object if
+ // the property is null or undefined.
+ c.on = c.on || {};
+
+ Y.fire(E_END, o.id);
+ if (c.on.end) {
+ evt = _subscribe('end', c);
+ evt.fire(o.id);
+ }
+
+ _destroy(o, c.xdr ? true : false );
+ }
+
+ /**
+ * @description Terminates a transaction due to an explicit abort or
+ * timeout.
+ *
+ * @method _ioCancel
+ * @private
+ * @static
+ * @param {object} o - Transaction object generated by _create().
+ * @param {string} s - Identifies timed out or aborted transaction.
+ *
+ * @return void
+ */
+ function _ioCancel(o, s) {
+ if (o && o.c) {
+ o.status = s;
+ o.c.abort();
+ }
+ }
+
+ /**
+ * @description Resends an XDR transaction, using the Flash tranport,
+ * if the native transport fails.
+ *
+ * @method _resend
+ * @private
+ * @static
+
+ * @param {object} o - Transaction object generated by _create().
+ * @param {string} uri - qualified path to transaction resource.
+ * @param {object} c - configuration object for the transaction.
+ *
+ * @return void
+ */
+ function _resend(o, uri, c) {
+ var id = parseInt(o.id);
+
+ _destroy(o);
+ c.xdr.use = 'flash';
+
+ return Y.io(uri, c, id);
+ }
+
+ /**
+ * @description Method that increments _transactionId for each transaction.
+ *
+ * @method _id
+ * @private
+ * @static
+ * @return int
+ */
+ function _id() {
+ var id = transactionId;
+
+ transactionId++;
+
+ return id;
+ }
+
+ /**
+ * @description Method that creates a unique transaction object for each
+ * request.
+ *
+ * @method _create
+ * @private
+ * @static
+ * @param {number} c - configuration object subset to determine if
+ * the transaction is an XDR or file upload,
+ * requiring an alternate transport.
+ * @param {number} i - transaction id
+ * @return object
+ */
+ function _create(c, i) {
+ var o = {};
+ o.id = Y.Lang.isNumber(i) ? i : _id();
+ c = c || {};
+
+ if (!c.use && !c.upload) {
+ o.c = _xhr();
+ }
+ else if (c.use) {
+ if (c.use === 'flash') {
+ o.c = Y.io._transport[c.use];
+ }
+ else if (c.use === 'native' && window.XDomainRequest) {
+ o.c = new XDomainRequest();
+ }
+ else {
+ o.c = _xhr();
+ }
+ }
+ else {
+ o.c = {};
+ }
+
+ return o;
+ };
+
+ /**
+ * @description Method that creates the XMLHttpRequest transport
+ *
+ * @method _xhr
+ * @private
+ * @static
+ * @return object
+ */
+ function _xhr() {
+ return w.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');
+ }
+
+ /**
+ * @description Method that concatenates string data for HTTP GET transactions.
+ *
+ * @method _concat
+ * @private
+ * @static
+ * @param {string} s - URI or root data.
+ * @param {string} d - data to be concatenated onto URI.
+ * @return int
+ */
+ function _concat(s, d) {
+ s += ((s.indexOf('?') == -1) ? '?' : '&') + d;
+ return s;
+ }
+
+ /**
+ * @description Method that stores default client headers for all transactions.
+ * If a label is passed with no value argument, the header will be deleted.
+ *
+ * @method _setHeader
+ * @private
+ * @static
+ * @param {string} l - HTTP header
+ * @param {string} v - HTTP header value
+ * @return int
+ */
+ function _setHeader(l, v) {
+ if (v) {
+ _headers[l] = v;
+ }
+ else {
+ delete _headers[l];
+ }
+ }
+
+ /**
+ * @description Method that sets all HTTP headers to be sent in a transaction.
+ *
+ * @method _setHeaders
+ * @private
+ * @static
+ * @param {object} o - XHR instance for the specific transaction.
+ * @param {object} h - HTTP headers for the specific transaction, as defined
+ * in the configuration object passed to YUI.io().
+ * @return void
+ */
+ function _setHeaders(o, h) {
+ var p;
+
+ for (p in _headers) {
+ if (_headers.hasOwnProperty(p)) {
+ if (h[p]) {
+ // Configuration headers will supersede IO preset headers,
+ // if headers match.
+ break;
+ }
+ else {
+ h[p] = _headers[p];
+ }
+ }
+ }
+
+ for (p in h) {
+ if (h.hasOwnProperty(p)) {
+ o.setRequestHeader(p, h[p]);
+ }
+ }
+ }
+
+ /**
+ * @description Starts timeout count if the configuration object
+ * has a defined timeout property.
+ *
+ * @method _startTimeout
+ * @private
+ * @static
+ * @param {object} o - Transaction object generated by _create().
+ * @param {object} c - Configuration object passed to YUI.io().
+ * @return void
+ */
+ function _startTimeout(o, timeout) {
+ _timeout[o.id] = w.setTimeout(function() { _ioCancel(o, 'timeout'); }, timeout);
+ }
+
+ /**
+ * @description Clears the timeout interval started by _startTimeout().
+ *
+ * @method _clearTimeout
+ * @private
+ * @static
+ * @param {number} id - Transaction id.
+ * @return void
+ */
+ function _clearTimeout(id) {
+ w.clearTimeout(_timeout[id]);
+ delete _timeout[id];
+ }
+
+ /**
+ * @description Event handler bound to onreadystatechange.
+ *
+ * @method _readyState
+ * @private
+ * @static
+ * @param {object} o - Transaction object generated by _create().
+ * @param {object} c - Configuration object passed to YUI.io().
+ * @return void
+ */
+ function _readyState(o, c) {
+ if (o.c.readyState === 4) {
+ if (c.timeout) {
+ _clearTimeout(o.id);
+ }
+
+ w.setTimeout(
+ function() {
+ _ioComplete(o, c);
+ _handleResponse(o, c);
+ }, 0);
+ }
+ }
+
+ /**
+ * @description Method that determines if a transaction response qualifies
+ * as success or failure, based on the response HTTP status code, and
+ * fires the appropriate success or failure events.
+ *
+ * @method _handleResponse
+ * @private
+ * @static
+ * @param {object} o - Transaction object generated by _create().
+ * @param {object} c - Configuration object passed to io().
+ * @return void
+ */
+ function _handleResponse(o, c) {
+ var status;
+ try{
+ if (o.c.status && o.c.status !== 0) {
+ status = o.c.status;
+ }
+ else {
+ status = 0;
+ }
+ }
+ catch(e) {
+ status = 0;
+ }
+
+ // IE reports HTTP 204 as HTTP 1223.
+ if (status >= 200 && status < 300 || status === 1223) {
+ _ioSuccess(o, c);
+ }
+ else {
+ _ioFailure(o, c);
+ }
+ }
+
+ function _destroy(o, transport) {
+ // IE, when using XMLHttpRequest as an ActiveX Object, will throw
+ // a "Type Mismatch" error if the event handler is set to "null".
+ if(w.XMLHttpRequest && !transport) {
+ if (o.c) {
+ o.c.onreadystatechange = null;
+ }
+ }
+
+ o.c = null;
+ o = null;
+ }
+
+ _io.start = _ioStart;
+ _io.complete = _ioComplete;
+ _io.success = _ioSuccess;
+ _io.failure = _ioFailure;
+ _io.end = _ioEnd;
+ _io._id = _id;
+ _io._timeout = _timeout;
+
+ //--------------------------------------
+ // Begin public interface definition
+ //--------------------------------------
+ /**
+ * @description Method that stores default client headers for all transactions.
+ * If a label is passed with no value argument, the header will be deleted.
+ * This is the interface for _setHeader().
+ *
+ * @method header
+ * @public
+ * @static
+ * @param {string} l - HTTP header
+ * @param {string} v - HTTP header value
+ * @return int
+ */
+ _io.header = _setHeader;
+
+ /**
+ * @description Method for requesting a transaction. This
+ * is the interface for _io().
+ *
+ * @method io
+ * @public
+ * @static
+ * @param {string} uri - qualified path to transaction resource.
+ * @param {object} c - configuration object for the transaction.
+ * @return object
+ */
+ Y.io = _io;
+ Y.io.http = _io;
+