# Yahoo! UI Library

### yui 3.0.0b1

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    (function() {

    /**
     * Provides a mechanism to fetch remote resources and
     * insert them into a document.
     * @module yui
     * @submodule get
     */

    var ua         = Y.UA,
        L          = Y.Lang,
        // PREFIX     = Y.guid(),
        TYPE_JS    = "text/javascript",
        TYPE_CSS   = "text/css",
        STYLESHEET = "stylesheet";

    /**
     * Fetches and inserts one or more script or link nodes into the document
     * @class Get
     * @static
     */
    Y.Get = function() {

        /**
         * hash of queues to manage multiple requests
         * @property queues
         * @private
         */
        var queues={},

        /**
         * queue index used to generate transaction ids
         * @property qidx
         * @type int
         * @private
         */
            qidx=0,

        /**
         * interal property used to prevent multiple simultaneous purge
         * processes
         * @property purging
         * @type boolean
         * @private
         */
            purging=false,

        /**
         * Generates an HTML element, this is not appended to a document
         * @method _node
         * @param type {string} the type of element
         * @param attr {string} the attributes
         * @param win {Window} optional window to create the element in
         * @return {HTMLElement} the generated node
         * @private
         */
        _node = function(type, attr, win) {
            var w = win || Y.config.win, d=w.document, n=d.createElement(type),
                i;

            for (i in attr) {
                if (attr[i] && attr.hasOwnProperty(i)) {
                    n.setAttribute(i, attr[i]);
                }
            }

            return n;
        },

        /**
         * Generates a link node
         * @method _linkNode
         * @param url {string} the url for the css file
         * @param win {Window} optional window to create the node in
         * @param attributes optional attributes collection to apply to the new node
         * @return {HTMLElement} the generated node
         * @private
         */
        _linkNode = function(url, win, attributes) {
            var o = {
                id:   Y.guid(),
                type: TYPE_CSS,
                rel:  STYLESHEET,
                href: url
            };
            if (attributes) {
                Y.mix(o, attributes);
            }
            return _node("link", o, win);
        },

        /**
         * Generates a script node
         * @method _scriptNode
         * @param url {string} the url for the script file
         * @param win {Window} optional window to create the node in
         * @param attributes optional attributes collection to apply to the new node
         * @return {HTMLElement} the generated node
         * @private
         */
        _scriptNode = function(url, win, attributes) {
            var o = {
                id:   Y.guid(),
                type: TYPE_JS,
                src:  url
            };

            if (attributes) {
                Y.mix(o, attributes);
            }

            return _node("script", o, win);
        },

        /**
         * Removes the nodes for the specified queue
         * @method _purge
         * @private
         */
        _purge = function(tId) {
            var q=queues[tId], n, l, d, h, s, i;
            if (q) {
                n = q.nodes;
                l = n.length;
                d = q.win.document;
                h = d.getElementsByTagName("head")[0];

                if (q.insertBefore) {
                    s = _get(q.insertBefore, tId);
                    if (s) {
                        h = s.parentNode;
                    }
                }

                for (i=0; i<l; i=i+1) {
                    h.removeChild(n[i]);
                }
            }
            q.nodes = [];
        },

        /**
         * Returns the data payload for callback functions
         * @method _returnData
         * @private
         */
        _returnData = function(q, msg, result) {
            return {
                    tId: q.tId,
                    win: q.win,
                    data: q.data,
                    nodes: q.nodes,
                    msg: msg,
                    statusText: result,
                    purge: function() {
                        _purge(this.tId);
                    }
                };
        },

        /**
         * The transaction is finished
         * @method _end
         * @param id {string} the id of the request
         * @private
         */
        _end = function(id, msg, result) {
            var q = queues[id], sc;
            if (q && q.onEnd) {
                sc = q.context || q;
                q.onEnd.call(sc, _returnData(q, msg, result));
            }
        },

        /*
         * The request failed, execute fail handler with whatever
         * was accomplished.  There isn't a failure case at the
         * moment unless you count aborted transactions
         * @method _fail
         * @param id {string} the id of the request
         * @private
         */
        _fail = function(id, msg) {

            Y.log("get failure: " + msg, "warn", "get");

            var q = queues[id], sc;
            if (q.timer) {
                q.timer.cancel();
            }

            // execute failure callback
            if (q.onFailure) {
                sc = q.context || q;
                q.onFailure.call(sc, _returnData(q, msg));
            }

            _end(id, msg, 'failure');
        },

        _get = function(nId, tId) {
            var q = queues[tId],
                n = (L.isString(nId)) ? q.win.document.getElementById(nId) : nId;
            if (!n) {
                _fail(tId, "target node not found: " + nId);
            }

            return n;
        },

        /**
         * The request is complete, so executing the requester's callback
         * @method _finish
         * @param id {string} the id of the request
         * @private
         */
        _finish = function(id) {
            Y.log("Finishing transaction " + id, "info", "get");
            var q = queues[id], msg, sc;
            if (q.timer) {
                q.timer.cancel();
            }
            q.finished = true;

            if (q.aborted) {
                msg = "transaction " + id + " was aborted";
                _fail(id, msg);
                return;
            }

            // execute success callback
            if (q.onSuccess) {
                sc = q.context || q;
                q.onSuccess.call(sc, _returnData(q));
            }

            _end(id, msg, 'OK');
        },

        /**
         * Timeout detected
         * @method _timeout
         * @param id {string} the id of the request
         * @private
         */
        _timeout = function(id) {
            Y.log("Timeout " + id, "info", "get");
            var q = queues[id], sc;
            if (q.onTimeout) {
                sc = q.context || q;
                q.onTimeout.call(sc, _returnData(q));
            }

            _end(id, 'timeout', 'timeout');
        },

        /**
         * Loads the next item for a given request
         * @method _next
         * @param id {string} the id of the request
         * @param loaded {string} the url that was just loaded, if any
         * @private
         */
        _next = function(id, loaded) {

            Y.log("_next: " + id + ", loaded: " + (loaded || "nothing"), "info", "get");

            var q = queues[id], msg, w, d, h, n, url, s;

            if (q.timer) {
                // Y.log('cancel timer');
                q.timer.cancel();
            }

            if (q.aborted) {
                msg = "transaction " + id + " was aborted";
                _fail(id, msg);
                return;
            }

            if (loaded) {
                q.url.shift();
                if (q.varName) {
                    q.varName.shift();
                }
            } else {
                // This is the first pass: make sure the url is an array
                q.url = (L.isString(q.url)) ? [q.url] : q.url;
                if (q.varName) {
                    q.varName = (L.isString(q.varName)) ? [q.varName] : q.varName;
                }
            }

            w = q.win;
            d = w.document;
            h = d.getElementsByTagName("head")[0];

            if (q.url.length === 0) {
                _finish(id);
                return;
            }

            url = q.url[0];

            // if the url is undefined, this is probably a trailing comma problem in IE
            if (!url) {
                q.url.shift();
                Y.log('skipping empty url');
                return _next(id);
            }

            Y.log("attempting to load " + url, "info", "get");

            if (q.timeout) {
                // Y.log('create timer');
                q.timer = L.later(q.timeout, q, _timeout, id);
            }

            if (q.type === "script") {
                n = _scriptNode(url, w, q.attributes);
            } else {
                n = _linkNode(url, w, q.attributes);
            }

            // track this node's load progress
            _track(q.type, n, id, url, w, q.url.length);

            // add the node to the queue so we can return it to the user supplied callback
            q.nodes.push(n);

            // add it to the head or insert it before 'insertBefore'
            if (q.insertBefore) {
                s = _get(q.insertBefore, id);
                if (s) {
                    s.parentNode.insertBefore(n, s);
                }
            } else {
                h.appendChild(n);
            }

            Y.log("Appending node: " + url, "info", "get");

            // FireFox does not support the onload event for link nodes, so there is
            // no way to make the css requests synchronous. This means that the css
            // rules in multiple files could be applied out of order in this browser
            // if a later request returns before an earlier one.  Safari too.
            if ((ua.webkit || ua.gecko) && q.type === "css") {
                _next(id, url);
            }
        },

        /**
         * Removes processed queues and corresponding nodes
         * @method _autoPurge
         * @private
         */
        _autoPurge = function() {

            if (purging) {
                return;
            }

            purging = true;

            var i, q;

            for (i in queues) {
                if (queues.hasOwnProperty(i)) {
                    q = queues[i];
                    if (q.autopurge && q.finished) {
                        _purge(q.tId);
                        delete queues[i];
                    }
                }
            }

            purging = false;
        },

        /**
         * Saves the state for the request and begins loading
         * the requested urls
         * @method queue
         * @param type {string} the type of node to insert
         * @param url {string} the url to load
         * @param opts the hash of options for this request
         * @private
         */
        _queue = function(type, url, opts) {

            opts = opts || {};

            var id = "q" + (qidx++), q,
                thresh = opts.purgethreshold || Y.Get.PURGE_THRESH;

            if (qidx % thresh === 0) {
                _autoPurge();
            }

            queues[id] = Y.merge(opts, {
                tId: id,
                type: type,
                url: url,
                finished: false,
                nodes: []
            });

            q           = queues[id];
            q.win       = q.win || Y.config.win;
            q.context   = q.context || q;
            q.autopurge = ("autopurge" in q) ? q.autopurge :
                          (type === "script") ? true : false;

            if (opts.charset) {
                q.attributes = q.attributes || {};
                q.attributes.charset = opts.charset;
            }

            L.later(0, q, _next, id);

            return {
                tId: id
            };
        },

        /**
         * Detects when a node has been loaded.  In the case of
         * script nodes, this does not guarantee that contained
         * script is ready to use.
         * @method _track
         * @param type {string} the type of node to track
         * @param n {HTMLElement} the node to track
         * @param id {string} the id of the request
         * @param url {string} the url that is being loaded
         * @param win {Window} the targeted window
         * @param qlength the number of remaining items in the queue,
         * including this one
         * @param trackfn {Function} function to execute when finished
         * the default is _next
         * @private
         */
        _track = function(type, n, id, url, win, qlength, trackfn) {
            var f = trackfn || _next;

            // IE supports the readystatechange event for script and css nodes
            // Opera only for script nodes.  Opera support onload for script
            // nodes, but this doesn't fire when there is a load failure.
            // The onreadystatechange appears to be a better way to respond
            // to both success and failure.
            if (ua.ie) {
                n.onreadystatechange = function() {
                    var rs = this.readyState;
                    if ("loaded" === rs || "complete" === rs) {
                        Y.log(id + " onreadstatechange " + url, "info", "get");
                        n.onreadystatechange = null;
                        f(id, url);
                    }
                };

            // webkit prior to 3.x is no longer supported
            } else if (ua.webkit) {

                if (type === "script") {
                    // Safari 3.x supports the load event for script nodes (DOM2)
                    n.addEventListener("load", function() {
                        Y.log(id + " DOM2 onload " + url, "info", "get");
                        f(id, url);
                    });
                }

            // FireFox and Opera support onload (but not DOM2 in FF) handlers for
            // script nodes.  Opera, but not FF, supports the onload event for link
            // nodes.
            } else {

                n.onload = function() {
                    Y.log(id + " onload " + url, "info", "get");
                    f(id, url);
                };

                n.onerror = function(e) {
                    _fail(id, e + ": " + url);
                };
            }
        };

        return {

            /**
             * The number of request required before an automatic purge.
             * Can be configured via the 'purgethreshold' config
             * property PURGE_THRESH
             * @static
             * @type int
             * @default 20
             * @private
             */
            PURGE_THRESH: 20,

            /**
             * Called by the the helper for detecting script load in Safari
             * @method _finalize
             * @static
             * @param id {string} the transaction id
             * @private
             */
            _finalize: function(id) {
                Y.log(id + " finalized ", "info", "get");
                L.later(0, null, _finish, id);
            },

            /**
             * Abort a transaction
             * @method abort
             * @static
             * @param o {string|object} Either the tId or the object returned from
             * script() or css()
             */
            abort: function(o) {
                var id = (L.isString(o)) ? o : o.tId,
                    q = queues[id];
                if (q) {
                    Y.log("Aborting " + id, "info", "get");
                    q.aborted = true;
                }
            },

            /**
             * Fetches and inserts one or more script nodes into the head
             * of the current document or the document in a specified window.
             *
             * @method script
             * @static
             * @param url {string|string[]} the url or urls to the script(s)
             * @param opts {object} Options:
             * <dl>
             * <dt>onSuccess</dt>
             * <dd>
             * callback to execute when the script(s) are finished loading
             * The callback receives an object back with the following
             * data:
             * <dl>
             * <dt>win</dt>
             * <dd>the window the script(s) were inserted into</dd>
             * <dt>data</dt>
             * <dd>the data object passed in when the request was made</dd>
             * <dt>nodes</dt>
             * <dd>An array containing references to the nodes that were
             * inserted</dd>
             * <dt>purge</dt>
             * <dd>A function that, when executed, will remove the nodes
             * that were inserted</dd>
             * <dt>
             * </dl>
             * </dd>
             * <dt>onTimeout</dt>
             * <dd>
             * callback to execute when a timeout occurs.
             * The callback receives an object back with the following
             * data:
             * <dl>
             * <dt>win</dt>
             * <dd>the window the script(s) were inserted into</dd>
             * <dt>data</dt>
             * <dd>the data object passed in when the request was made</dd>
             * <dt>nodes</dt>
             * <dd>An array containing references to the nodes that were
             * inserted</dd>
             * <dt>purge</dt>
             * <dd>A function that, when executed, will remove the nodes
             * that were inserted</dd>
             * <dt>
             * </dl>
             * </dd>
             * <dt>onEnd</dt>
             * <dd>a function that executes when the transaction finishes, regardless of the exit path</dd>
             * <dt>onFailure</dt>
             * <dd>
             * callback to execute when the script load operation fails
             * The callback receives an object back with the following
             * data:
             * <dl>
             * <dt>win</dt>
             * <dd>the window the script(s) were inserted into</dd>
             * <dt>data</dt>
             * <dd>the data object passed in when the request was made</dd>
             * <dt>nodes</dt>
             * <dd>An array containing references to the nodes that were
             * inserted successfully</dd>
             * <dt>purge</dt>
             * <dd>A function that, when executed, will remove any nodes
             * that were inserted</dd>
             * <dt>
             * </dl>
             * </dd>
             * <dt>context</dt>
             * <dd>the execution context for the callbacks</dd>
             * <dt>win</dt>
             * <dd>a window other than the one the utility occupies</dd>
             * <dt>autopurge</dt>
             * <dd>
             * setting to true will let the utilities cleanup routine purge
             * the script once loaded
             * </dd>
             * <dt>purgethreshold</dt>
             * <dd>
             * The number of transaction before autopurge should be initiated
             * </dd>
             * <dt>data</dt>
             * <dd>
             * data that is supplied to the callback when the script(s) are
             * loaded.
             * </dd>
             * <dt>insertBefore</dt>
             * <dd>node or node id that will become the new node's nextSibling</dd>
             * </dl>
             * <dt>charset</dt>
             * <dd>Node charset, default utf-8 (deprecated, use the attributes config)</dd>
             * <dt>attributes</dt>
             * <dd>An object literal containing additional attributes to add to the link tags</dd>
             * <dt>timeout</dt>
             * <dd>Number of milliseconds to wait before aborting and firing the timeout event</dd>
             * <pre>
             * &nbsp;&nbsp;Y.Get.script(
             * &nbsp;&nbsp;["http://yui.yahooapis.com/2.5.2/build/yahoo/yahoo-min.js",
             * &nbsp;&nbsp;&nbsp;"http://yui.yahooapis.com/2.5.2/build/event/event-min.js"], &#123;
             * &nbsp;&nbsp;&nbsp;&nbsp;onSuccess: function(o) &#123;
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;this.log("won't cause error because Y is the context");
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Y.log(o.data); // foo
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Y.log(o.nodes.length === 2) // true
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// o.purge(); // optionally remove the script nodes immediately
             * &nbsp;&nbsp;&nbsp;&nbsp;&#125;,
             * &nbsp;&nbsp;&nbsp;&nbsp;onFailure: function(o) &#123;
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Y.log("transaction failed");
             * &nbsp;&nbsp;&nbsp;&nbsp;&#125;,
             * &nbsp;&nbsp;&nbsp;&nbsp;onTimeout: function(o) &#123;
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Y.log("transaction timed out");
             * &nbsp;&nbsp;&nbsp;&nbsp;&#125;,
             * &nbsp;&nbsp;&nbsp;&nbsp;data: "foo",
             * &nbsp;&nbsp;&nbsp;&nbsp;timeout: 10000, // 10 second timeout
             * &nbsp;&nbsp;&nbsp;&nbsp;context: Y, // make the YUI instance
             * &nbsp;&nbsp;&nbsp;&nbsp;// win: otherframe // target another window/frame
             * &nbsp;&nbsp;&nbsp;&nbsp;autopurge: true // allow the utility to choose when to remove the nodes
             * &nbsp;&nbsp;&nbsp;&nbsp;purgetheshold: 1 // purge previous transaction before next transaction
             * &nbsp;&nbsp;&#125;);
             * </pre>
             * @return {tId: string} an object containing info about the transaction
             */
            script: function(url, opts) {
                return _queue("script", url, opts);
            },

            /**
             * Fetches and inserts one or more css link nodes into the
             * head of the current document or the document in a specified
             * window.
             * @method css
             * @static
             * @param url {string} the url or urls to the css file(s)
             * @param opts Options:
             * <dl>
             * <dt>onSuccess</dt>
             * <dd>
             * callback to execute when the css file(s) are finished loading
             * The callback receives an object back with the following
             * data:
             * <dl>win</dl>
             * <dd>the window the link nodes(s) were inserted into</dd>
             * <dt>data</dt>
             * <dd>the data object passed in when the request was made</dd>
             * <dt>nodes</dt>
             * <dd>An array containing references to the nodes that were
             * inserted</dd>
             * <dt>purge</dt>
             * <dd>A function that, when executed, will remove the nodes
             * that were inserted</dd>
             * <dt>
             * </dl>
             * </dd>
             * <dt>context</dt>
             * <dd>the execution context for the callbacks</dd>
             * <dt>win</dt>
             * <dd>a window other than the one the utility occupies</dd>
             * <dt>data</dt>
             * <dd>
             * data that is supplied to the callbacks when the nodes(s) are
             * loaded.
             * </dd>
             * <dt>insertBefore</dt>
             * <dd>node or node id that will become the new node's nextSibling</dd>
             * <dt>charset</dt>
             * <dd>Node charset, default utf-8 (deprecated, use the attributes config)</dd>
             * <dt>attributes</dt>
             * <dd>An object literal containing additional attributes to add to the link tags</dd>
             * </dl>
             * <pre>
             *      Y.Get.css("http://yui.yahooapis.com/2.3.1/build/menu/assets/skins/sam/menu.css");
             * </pre>
             * <pre>
             * &nbsp;&nbsp;Y.Get.css(
             * &nbsp;&nbsp;["http://yui.yahooapis.com/2.3.1/build/menu/assets/skins/sam/menu.css",
             * &nbsp;&nbsp;&nbsp;"http://yui.yahooapis.com/2.3.1/build/logger/assets/skins/sam/logger.css"], &#123;
             * &nbsp;&nbsp;&nbsp;&nbsp;insertBefore: 'custom-styles' // nodes will be inserted before the specified node
             * &nbsp;&nbsp;&#125;);
             * </pre>
             * @return {tId: string} an object containing info about the transaction
             */
            css: function(url, opts) {
                return _queue("css", url, opts);
            }
        };
    }();

    })();

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