    /**
     * @author Ed Spencer
     *
     * The JSON Reader is used by a Proxy to read a server response that is sent back in JSON format. This usually
     * happens as a result of loading a Store - for example we might create something like this:
     *
     *     Ext.define('User', {
     *         extend: 'Ext.data.Model',
     *         fields: ['id', 'name', 'email']
     *     });
     *
     *     var store = Ext.create('Ext.data.Store', {
     *         model: 'User',
     *         proxy: {
     *             type: 'ajax',
     *             url : 'users.json',
     *             reader: {
     *                 type: 'json'
     *             }
     *         }
     *     });
     *
     * 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.
     *
     * We created the simplest type of JSON Reader possible by simply telling our {@link Ext.data.Store Store}'s
     * {@link Ext.data.proxy.Proxy Proxy} that we want a JSON Reader. The Store automatically passes the configured model to the
     * Store, so it is as if we passed this instead:
     *
     *     reader: {
     *         type : 'json',
     *         model: 'User'
     *     }
     *
     * The reader we set up is ready to read data from our server - at the moment it will accept a response like this:
     *
     *     [
     *         {
     *             "id": 1,
     *             "name": "Ed Spencer",
     *             "email": "ed@sencha.com"
     *         },
     *         {
     *             "id": 2,
     *             "name": "Abe Elias",
     *             "email": "abe@sencha.com"
     *         }
     *     ]
     *
     * ## Reading other JSON formats
     *
     * If you already have your JSON format defined and it doesn't look quite like what we have above, you can usually
     * pass JsonReader a couple of configuration options to make it parse your format. For example, we can use the
     * {@link #cfg-root} configuration to parse data that comes back like this:
     *
     *     {
     *         "users": [
     *            {
     *                "id": 1,
     *                "name": "Ed Spencer",
     *                "email": "ed@sencha.com"
     *            },
     *            {
     *                "id": 2,
     *                "name": "Abe Elias",
     *                "email": "abe@sencha.com"
     *            }
     *         ]
     *     }
     *
     * To parse this we just pass in a {@link #root} configuration that matches the 'users' above:
     *
     *     reader: {
     *         type: 'json',
     *         root: 'users'
     *     }
     *
     * Sometimes the JSON structure is even more complicated. Document databases like CouchDB often provide metadata
     * around each record inside a nested structure like this:
     *
     *     {
     *         "total": 122,
     *         "offset": 0,
     *         "users": [
     *             {
     *                 "id": "ed-spencer-1",
     *                 "value": 1,
     *                 "user": {
     *                     "id": 1,
     *                     "name": "Ed Spencer",
     *                     "email": "ed@sencha.com"
     *                 }
     *             }
     *         ]
     *     }
     *
     * In the case above the record data is nested an additional level inside the "users" array as each "user" item has
     * additional metadata surrounding it ('id' and 'value' in this case). To parse data out of each "user" item in the
     * JSON above we need to specify the {@link #record} configuration like this:
     *
     *     reader: {
     *         type  : 'json',
     *         root  : 'users',
     *         record: 'user'
     *     }
     *
     * ## Response MetaData
     *
     * The server can return metadata in its response, in addition to the record data, that describe attributes
     * of the data set itself or are used to reconfigure the Reader. To pass metadata in the response you simply
     * add a `metaData` attribute to the root of the response data. The metaData attribute can contain anything,
     * but supports a specific set of properties that are handled by the Reader if they are present:
     *
     * - {@link #root}: the property name of the root response node containing the record data
     * - {@link #idProperty}: property name for the primary key field of the data
     * - {@link #totalProperty}: property name for the total number of records in the data
     * - {@link #successProperty}: property name for the success status of the response
     * - {@link #messageProperty}: property name for an optional response message
     * - {@link Ext.data.Model#cfg-fields fields}: Config used to reconfigure the Model's fields before converting the
     * response data into records
     *
     * An initial Reader configuration containing all of these properties might look like this ("fields" would be
     * included in the Model definition, not shown):
     *
     *     reader: {
     *         type : 'json',
     *         root : 'root',
     *         idProperty     : 'id',
     *         totalProperty  : 'total',
     *         successProperty: 'success',
     *         messageProperty: 'message'
     *     }
     *
     * If you were to pass a response object containing attributes different from those initially defined above, you could
     * use the `metaData` attribute to reconifgure the Reader on the fly. For example:
     *
     *     {
     *         "count": 1,
     *         "ok": true,
     *         "msg": "Users found",
     *         "users": [{
     *             "userId": 123,
     *             "name": "Ed Spencer",
     *             "email": "ed@sencha.com"
     *         }],
     *         "metaData": {
     *             "root": "users",
     *             "idProperty": 'userId',
     *             "totalProperty": 'count',
     *             "successProperty": 'ok',
     *             "messageProperty": 'msg'
     *         }
     *     }
     *
     * You can also place any other arbitrary data you need into the `metaData` attribute which will be ignored by the Reader,
     * but will be accessible via the Reader's {@link #metaData} property (which is also passed to listeners via the Proxy's
     * {@link Ext.data.proxy.Proxy#metachange metachange} event (also relayed by the {@link Ext.data.AbstractStore#metachange
     * store}). Application code can then process the passed metadata in any way it chooses.
     *
     * A simple example for how this can be used would be customizing the fields for a Model that is bound to a grid. By passing
     * the `fields` property the Model will be automatically updated by the Reader internally, but that change will not be
     * reflected automatically in the grid unless you also update the column configuration. You could do this manually, or you
     * could simply pass a standard grid {@link Ext.panel.Table#columns column} config object as part of the `metaData` attribute
     * and then pass that along to the grid. Here's a very simple example for how that could be accomplished:
     *
     *     // response format:
     *     {
     *         ...
     *         "metaData": {
     *             "fields": [
     *                 { "name": "userId", "type": "int" },
     *                 { "name": "name", "type": "string" },
     *                 { "name": "birthday", "type": "date", "dateFormat": "Y-j-m" },
     *             ],
     *             "columns": [
     *                 { "text": "User ID", "dataIndex": "userId", "width": 40 },
     *                 { "text": "User Name", "dataIndex": "name", "flex": 1 },
     *                 { "text": "Birthday", "dataIndex": "birthday", "flex": 1, "format": 'Y-j-m', "xtype": "datecolumn" }
     *             ]
     *         }
     *     }
     *
     * The Reader will automatically read the meta fields config and rebuild the Model based on the new fields, but to handle
     * the new column configuration you would need to handle the metadata within the application code. This is done simply enough
     * by handling the metachange event on either the store or the proxy, e.g.:
     *
     *     var store = Ext.create('Ext.data.Store', {
     *         ...
     *         listeners: {
     *             'metachange': function(store, meta) {
     *                 myGrid.reconfigure(store, meta.columns);
     *             }
     *         }
     *     });
     *
     */
    Ext.define('Ext.data.reader.Json', {
        extend: 'Ext.data.reader.Reader',
        alternateClassName: 'Ext.data.JsonReader',
        alias : 'reader.json',

        root: '',

        /**
         * @cfg {String} record The optional location within the JSON response that the record data itself can be found at.
         * See the JsonReader intro docs for more details. This is not often needed.
         */

        /**
         * @cfg {String} [metaProperty="metaData"]
         * Name of the property from which to retrieve the `metaData` attribute. See {@link #metaData}.
         */
        metaProperty: 'metaData',

        /**
         * @cfg {Boolean} useSimpleAccessors True to ensure that field names/mappings are treated as literals when
         * reading values.
         *
         * For example, by default, using the mapping "foo.bar.baz" will try and read a property foo from the root, then a property bar
         * from foo, then a property baz from bar. Setting the simple accessors to true will read the property with the name
         * "foo.bar.baz" direct from the root object.
         */
        useSimpleAccessors: false,

        /**
         * Reads a JSON object and returns a ResultSet. Uses the internal getTotal and getSuccess extractors to
         * retrieve meta data from the response, and extractData to turn the JSON data into model instances.
         * @param {Object} data The raw JSON data
         * @return {Ext.data.ResultSet} A ResultSet containing model instances and meta data about the results
         */
        readRecords: function(data) {
            var me = this,
                meta;

            //this has to be before the call to super because we use the meta data in the superclass readRecords
            if (me.getMeta) {
                meta = me.getMeta(data);
                if (meta) {
                    me.onMetaChange(meta);
                }
            } else if (data.metaData) {
                me.onMetaChange(data.metaData);
            }

            /**
             * @property {Object} jsonData
             * A copy of this.rawData.
             * @deprecated Will be removed in Ext JS 5.0. This is just a copy of this.rawData - use that instead.
             */
            me.jsonData = data;
            return me.callParent([data]);
        },

        //inherit docs
        getResponseData: function(response) {
            var data, error;

            try {
                data = Ext.decode(response.responseText);
                return this.readRecords(data);
            } catch (ex) {
                error = new Ext.data.ResultSet({
                    total  : 0,
                    count  : 0,
                    records: [],
                    success: false,
                    message: ex.message
                });

                this.fireEvent('exception', this, response, error);

                Ext.Logger.warn('Unable to parse the JSON returned by the server');

                return error;
            }
        },

        //inherit docs
        buildExtractors : function() {
            var me = this,
                metaProp = me.metaProperty;

            me.callParent(arguments);

            if (me.root) {
                me.getRoot = me.createAccessor(me.root);
            } else {
                me.getRoot = Ext.identityFn;
            }

            if (metaProp) {
                me.getMeta = me.createAccessor(metaProp);
            }
        },

        /**
         * @private
         * We're just preparing the data for the superclass by pulling out the record objects we want. If a {@link #record}
         * was specified we have to pull those out of the larger JSON object, which is most of what this function is doing
         * @param {Object} root The JSON root node
         * @return {Ext.data.Model[]} The records
         */
        extractData: function(root) {
            var recordName = this.record,
                data = [],
                length, i;

            if (recordName) {
                length = root.length;

                if (!length && Ext.isObject(root)) {
                    length = 1;
                    root = [root];
                }

                for (i = 0; i < length; i++) {
                    data[i] = root[i][recordName];
                }
            } else {
                data = root;
            }
            return this.callParent([data]);
        },

        /**
         * @private
         * @method
         * Returns an accessor function for the given property string. Gives support for properties such as the following:
         *
         * - 'someProperty'
         * - 'some.property'
         * - '["someProperty"]'
         * - 'values[0]'
         *
         * This is used by {@link #buildExtractors} to create optimized extractor functions for properties that are looked
         * up directly on the source object (e.g. {@link #successProperty}, {@link #messageProperty}, etc.).
         */
        createAccessor: (function() {
            var re = /[\[\.]/;

            return function(expr) {
                if (Ext.isEmpty(expr)) {
                    return Ext.emptyFn;
                }
                if (Ext.isFunction(expr)) {
                    return expr;
                }
                if (this.useSimpleAccessors !== true) {
                    var i = String(expr).search(re);
                    if (i >= 0) {
                        return Ext.functionFactory('obj', 'return obj' + (i > 0 ? '.' : '') + expr);
                    }
                }
                return function(obj) {
                    return obj[expr];
                };
            };
        }()),

        /**
         * @private
         * @method
         * Returns an accessor expression for the passed Field. Gives support for properties such as the following:
         *
         * - 'someProperty'
         * - 'some.property'
         * - '["someProperty"]'
         * - 'values[0]'
         *
         * This is used by {@link #buildRecordDataExtractor} to create optimized extractor expressions when converting raw
         * data into model instances. This method is used at the field level to dynamically map values to model fields.
         */
        createFieldAccessExpression: (function() {
            var re = /[\[\.]/;

            return function(field, fieldVarName, dataName) {
                var mapping = field.mapping,
                    hasMap = mapping || mapping === 0,
                    map    = hasMap ? mapping : field.name,
                    result,
                    operatorIndex;

                // mapping: false means that the Field will never be read from server data.
                if (mapping === false) {
                    return;
                }

                if (typeof map === 'function') {
                    result = fieldVarName + '.mapping(' + dataName + ', this)';
                } else if (this.useSimpleAccessors === true || ((operatorIndex = String(map).search(re)) < 0)) {
                    if (!hasMap || isNaN(map)) {
                        // If we don't provide a mapping, we may have a field name that is numeric
                        map = '"' + map + '"';
                    }
                    result = dataName + "[" + map + "]";
                } else if (operatorIndex === 0) {
                    // If it matched at index 0 then it must be bracket syntax (e.g. ["foo"]). In this case simply
                    // join the two, e.g. 'field["foo"]':
                    result = dataName + map;
                } else {
                    // If it matched at index > 0 it must be either dot syntax (e.g. field.foo) or a values array
                    // item (e.g. values[0]). For the latter, we can simply concatenate the values reference to
                    // the source directly like 'field.values[0]'. For dot notation we have to support arbitrary
                    // levels (field.foo.bar), any of which could be null or undefined, so we have to create the
                    // returned value such that the references will be assigned defensively in the calling code.
                    // The output should look like 'field.foo && field.foo.bar' in that case.
                    var parts = map.split('.'),
                        len = parts.length,
                        i = 1,
                        tempResult = dataName + '.' + parts[0],
                        buffer = [tempResult]; // for 'field.values[0]' this will be the returned result

                    for (; i < len; i++) {
                        tempResult += '.' + parts[i];
                        buffer.push(tempResult);
                    }
                    result = buffer.join(' && ');
                }
                return result;
            };
        }())
    });