/**
 * @author Ed Spencer
 * @class Ext.data.reader.Xml
 * @extends Ext.data.reader.Reader
 * 
 * <p>The XML Reader is used by a Proxy to read a server response that is sent back in XML format. This usually
 * happens as a result of loading a Store - for example we might create something like this:</p>
 * 
<pre><code>
Ext.define('User', {
    extend: 'Ext.data.Model',
    fields: ['id', 'name', 'email']
});

var store = new Ext.data.Store({
    model: 'User',
    proxy: {
        type: 'ajax',
        url : 'users.xml',
        reader: {
            type: 'xml',
            record: 'user'
        }
    }
});
</code></pre>
 * 
 * <p>The example above creates a 'User' model. Models are explained in the {@link Ext.data.Model Model} docs if you're
 * not already familiar with them.</p>
 * 
 * <p>We created the simplest type of XML Reader possible by simply telling our {@link Ext.data.Store Store}'s 
 * {@link Ext.data.proxy.Proxy Proxy} that we want a XML Reader. The Store automatically passes the configured model to the
 * Store, so it is as if we passed this instead:
 * 
<pre><code>
reader: {
    type : 'xml',
    model: 'User',
    record: 'user'
}
</code></pre>
 * 
 * <p>The reader we set up is ready to read data from our server - at the moment it will accept a response like this:</p>
 *
<pre><code>
&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;user&gt;
    &lt;id&gt;1&lt;/id&gt;
    &lt;name&gt;Ed Spencer&lt;/name&gt;
    &lt;email&gt;ed@sencha.com&lt;/email&gt;
&lt;/user&gt;
&lt;user&gt;
    &lt;id&gt;2&lt;/id&gt;
    &lt;name&gt;Abe Elias&lt;/name&gt;
    &lt;email&gt;abe@sencha.com&lt;/email&gt;
&lt;/user&gt;
</code></pre>
 * 
 * <p>The XML Reader uses the configured {@link #record} option to pull out the data for each record - in this case we
 * set record to 'user', so each &lt;user&gt; above will be converted into a User model.</p>
 * 
 * <p><u>Reading other XML formats</u></p>
 * 
 * <p>If you already have your XML format defined and it doesn't look quite like what we have above, you can usually
 * pass XmlReader a couple of configuration options to make it parse your format. For example, we can use the 
 * {@link #root} configuration to parse data that comes back like this:</p>
 * 
<pre><code>
&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;users&gt;
    &lt;user&gt;
        &lt;id&gt;1&lt;/id&gt;
        &lt;name&gt;Ed Spencer&lt;/name&gt;
        &lt;email&gt;ed@sencha.com&lt;/email&gt;
    &lt;/user&gt;
    &lt;user&gt;
        &lt;id&gt;2&lt;/id&gt;
        &lt;name&gt;Abe Elias&lt;/name&gt;
        &lt;email&gt;abe@sencha.com&lt;/email&gt;
    &lt;/user&gt;
&lt;/users&gt;
</code></pre>
 * 
 * <p>To parse this we just pass in a {@link #root} configuration that matches the 'users' above:</p>
 * 
<pre><code>
reader: {
    type  : 'xml',
    root  : 'users',
    record: 'user'
}
</code></pre>
 * 
 * <p>Note that XmlReader doesn't care whether your {@link #root} and {@link #record} elements are nested deep inside
 * a larger structure, so a response like this will still work:
 * 
<pre><code>
&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;deeply&gt;
    &lt;nested&gt;
        &lt;xml&gt;
            &lt;users&gt;
                &lt;user&gt;
                    &lt;id&gt;1&lt;/id&gt;
                    &lt;name&gt;Ed Spencer&lt;/name&gt;
                    &lt;email&gt;ed@sencha.com&lt;/email&gt;
                &lt;/user&gt;
                &lt;user&gt;
                    &lt;id&gt;2&lt;/id&gt;
                    &lt;name&gt;Abe Elias&lt;/name&gt;
                    &lt;email&gt;abe@sencha.com&lt;/email&gt;
                &lt;/user&gt;
            &lt;/users&gt;
        &lt;/xml&gt;
    &lt;/nested&gt;
&lt;/deeply&gt;
</code></pre>
 * 
 * <p><u>Response metadata</u></p>
 * 
 * <p>The server can return additional data in its response, such as the {@link #totalProperty total number of records} 
 * and the {@link #successProperty success status of the response}. These are typically included in the XML response
 * like this:</p>
 * 
<pre><code>
&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;total&gt;100&lt;/total&gt;
&lt;success&gt;true&lt;/success&gt;
&lt;users&gt;
    &lt;user&gt;
        &lt;id&gt;1&lt;/id&gt;
        &lt;name&gt;Ed Spencer&lt;/name&gt;
        &lt;email&gt;ed@sencha.com&lt;/email&gt;
    &lt;/user&gt;
    &lt;user&gt;
        &lt;id&gt;2&lt;/id&gt;
        &lt;name&gt;Abe Elias&lt;/name&gt;
        &lt;email&gt;abe@sencha.com&lt;/email&gt;
    &lt;/user&gt;
&lt;/users&gt;
</code></pre>
 * 
 * <p>If these properties are present in the XML response they can be parsed out by the XmlReader and used by the
 * Store that loaded it. We can set up the names of these properties by specifying a final pair of configuration 
 * options:</p>
 * 
<pre><code>
reader: {
    type: 'xml',
    root: 'users',
    totalProperty  : 'total',
    successProperty: 'success'
}
</code></pre>
 * 
 * <p>These final options are not necessary to make the Reader work, but can be useful when the server needs to report
 * an error or if it needs to indicate that there is a lot of data available of which only a subset is currently being
 * returned.</p>
 * 
 * <p><u>Response format</u></p>
 * 
 * <p><b>Note:</b> in order for the browser to parse a returned XML document, the Content-Type header in the HTTP 
 * response must be set to "text/xml" or "application/xml". This is very important - the XmlReader will not
 * work correctly otherwise.</p>
 */
Ext.define('Ext.data.reader.Xml', {
    extend: 'Ext.data.reader.Reader',
    alternateClassName: 'Ext.data.XmlReader',
    alias : 'reader.xml',
    
    /**
     * @cfg {String} record The DomQuery path to the repeated element which contains record information.
     */

    /**
     * @private
     * Creates a function to return some particular key of data from a response. The totalProperty and
     * successProperty are treated as special cases for type casting, everything else is just a simple selector.
     * @param {String} key
     * @return {Function}
     */
    createAccessor: function(expr) {
        var me = this;
        
        if (Ext.isEmpty(expr)) {
            return Ext.emptyFn;
        }
        
        if (Ext.isFunction(expr)) {
            return expr;
        }
        
        return function(root) {
            var node = Ext.DomQuery.selectNode(expr, root),
                val = me.getNodeValue(node);
                
            return Ext.isEmpty(val) ? null : val;
        };
    },
    
    getNodeValue: function(node) {
        var val;
        if (node && node.firstChild) {
            val = node.firstChild.nodeValue;
        }
        return val || null;
    },

    //inherit docs
    getResponseData: function(response) {
        var xml = response.responseXML;

        //<debug>
        if (!xml) {
            Ext.Error.raise({
                response: response,
                msg: 'XML data not found in the response'
            });
        }
        //</debug>

        return xml;
    },

    /**
     * Normalizes the data object
     * @param {Object} data The raw data object
     * @return {Object} Returns the documentElement property of the data object if present, or the same object if not
     */
    getData: function(data) {
        return data.documentElement || data;
    },

    /**
     * @private
     * Given an XML object, returns the Element that represents the root as configured by the Reader's meta data
     * @param {Object} data The XML data object
     * @return {Element} The root node element
     */
    getRoot: function(data) {
        var nodeName = data.nodeName,
            root     = this.root;
        
        if (!root || (nodeName && nodeName == root)) {
            return data;
        } else if (Ext.DomQuery.isXml(data)) {
            // This fix ensures we have XML data
            // Related to TreeStore calling getRoot with the root node, which isn't XML
            // Probably should be resolved in TreeStore at some point
            return Ext.DomQuery.selectNode(root, data);
        }
    },

    /**
     * @private
     * We're just preparing the data for the superclass by pulling out the record nodes we want
     * @param {Element} root The XML root node
     * @return {Array} The records
     */
    extractData: function(root) {
        var recordName = this.record;
        
        //<debug>
        if (!recordName) {
            Ext.Error.raise('Record is a required parameter');
        }
        //</debug>
        
        if (recordName != root.nodeName) {
            root = Ext.DomQuery.select(recordName, root);
        } else {
            root = [root];
        }
        return this.callParent([root]);
    },
    
    /**
     * @private
     * See Ext.data.reader.Reader's getAssociatedDataRoot docs
     * @param {Mixed} data The raw data object
     * @param {String} associationName The name of the association to get data for (uses associationKey if present)
     * @return {Mixed} The root
     */
    getAssociatedDataRoot: function(data, associationName) {
        return Ext.DomQuery.select(associationName, data)[0];
    },

    /**
     * Parses an XML document and returns a ResultSet containing the model instances
     * @param {Object} doc Parsed XML document
     * @return {Ext.data.ResultSet} The parsed result set
     */
    readRecords: function(doc) {
        //it's possible that we get passed an array here by associations. Make sure we strip that out (see Ext.data.reader.Reader#readAssociated)
        if (Ext.isArray(doc)) {
            doc = doc[0];
        }
        
        /**
         * DEPRECATED - will be removed in Ext JS 5.0. This is just a copy of this.rawData - use that instead
         * @property xmlData
         * @type Object
         */
        this.xmlData = doc;
        return this.callParent([doc]);
    }
});
