/**
 * @author Ed Spencer
 * @class Ext.data.Proxy
 * @extends Ext.util.Observable
 * 
 * 
Proxies are used by {@link Ext.data.Store Stores} to handle the loading and saving of {@link Ext.data.Model Model} data.
 * Usually developers will not need to create or interact with proxies directly.
 * 
Types of Proxy
 * 
 * 
There are two main types of Proxy - {@link Ext.data.ClientProxy Client} and {@link Ext.data.ServerProxy Server}. The Client proxies
 * save their data locally and include the following subclasses:
 * 
 * 

 * 
{@link Ext.data.LocalStorageProxy LocalStorageProxy} - saves its data to localStorage if the browser supports it
 * 
{@link Ext.data.SessionStorageProxy SessionStorageProxy} - saves its data to sessionStorage if the browsers supports it
 * 
{@link Ext.data.MemoryProxy MemoryProxy} - holds data in memory only, any data is lost when the page is refreshed
 * 
 * 
 * 
The Server proxies save their data by sending requests to some remote server. These proxies include:
 * 
 * 

 * 
{@link Ext.data.AjaxProxy AjaxProxy} - sends requests to a server on the same domain
 * 
{@link Ext.data.ScriptTagProxy ScriptTagProxy} - uses JSON-P to send requests to a server on a different domain
 * 
 * 
 * 
Proxies operate on the principle that all operations performed are either Create, Read, Update or Delete. These four operations 
 * are mapped to the methods {@link #create}, {@link #read}, {@link #update} and {@link #destroy} respectively. Each Proxy subclass 
 * implements these functions.
 * 
 * 
The CRUD methods each expect an {@link Ext.data.Operation operation} object as the sole argument. The Operation encapsulates 
 * information about the action the Store wishes to perform, the {@link Ext.data.Model model} instances that are to be modified, etc.
 * See the {@link Ext.data.Operation Operation} documentation for more details. Each CRUD method also accepts a callback function to be 
 * called asynchronously on completion.
 * 
 * 
Proxies also support batching of Operations via a {@link Ext.data.Batch batch} object, invoked by the {@link #batch} method.
 * 
 * @constructor
 * Creates the Proxy
 * @param {Object} config Optional config object
 */
Ext.data.Proxy = Ext.extend(Ext.util.Observable, {
    
/**
     * @cfg {String} batchOrder
     * Comma-separated ordering 'create', 'update' and 'destroy' actions when batching. Override this
     * to set a different order for the batched CRUD actions to be executed in. Defaults to 'create,update,destroy'
     */
    batchOrder: 'create,update,destroy',
    
    
/**
     * @cfg {String} defaultReaderType The default registered reader type. Defaults to 'json'
     */
    defaultReaderType: 'json',
    
    
/**
     * @cfg {String} defaultWriterType The default registered writer type. Defaults to 'json'
     */
    defaultWriterType: 'json',
    
    constructor: function(config) {
        config = config || {};
        
        if (config.model == undefined) {
            delete config.model;
        }

        Ext.data.Proxy.superclass.constructor.call(this, config);
        
        if (this.model != undefined && !(this.model instanceof Ext.data.Model)) {
            this.setModel(this.model);
        }
    },
    
    
/**
     * Sets the model associated with this proxy. This will only usually be called by a Store
     * @param {String|Ext.data.Model} model The new model. Can be either the model name string,
     * or a reference to the model's constructor
     * @param {Boolean} setOnStore Sets the new model on the associated Store, if one is present
     */
    setModel: function(model, setOnStore) {
        this.model = Ext.ModelMgr.getModel(model);
        
        var reader = this.reader,
            writer = this.writer;
        
        this.setReader(reader);
        this.setWriter(writer);
        
        if (setOnStore && this.store) {
            this.store.setModel(this.model);
        }
    },
    
    
/**
     * Returns the model attached to this Proxy
     * @return {Ext.data.Model} The model
     */
    getModel: function() {
        return this.model;
    },
    
    
/**
     * Sets the Proxy's Reader by string, config object or Reader instance
     * @param {String|Object|Ext.data.Reader} reader The new Reader, which can be either a type string, a configuration object
     * or an Ext.data.Reader instance
     * @return {Ext.data.Reader} The attached Reader object
     */
    setReader: function(reader) {
        if (reader == undefined || typeof reader == 'string') {
            reader = {
                type: reader
            };
        }

        if (!(reader instanceof Ext.data.Reader)) {
            Ext.applyIf(reader, {
                proxy: this,
                model: this.model,
                type : this.defaultReaderType
            });

            reader = Ext.data.ReaderMgr.create(reader);
        }
        
        this.reader = reader;
        
        return this.reader;
    },
    
    
/**
     * Returns the reader currently attached to this proxy instance
     * @return {Ext.data.Reader} The Reader instance
     */
    getReader: function() {
        return this.reader;
    },
    
    
/**
     * Sets the Proxy's Writer by string, config object or Writer instance
     * @param {String|Object|Ext.data.Writer} writer The new Writer, which can be either a type string, a configuration object
     * or an Ext.data.Writer instance
     * @return {Ext.data.Writer} The attached Writer object
     */
    setWriter: function(writer) {
        if (writer == undefined || typeof writer == 'string') {
            writer = {
                type: writer
            };
        }

        if (!(writer instanceof Ext.data.Writer)) {
            Ext.applyIf(writer, {
                model: this.model,
                type : this.defaultWriterType
            });

            writer = Ext.data.WriterMgr.create(writer);
        }
        
        this.writer = writer;
        
        return this.writer;
    },
    
    
/**
     * Returns the writer currently attached to this proxy instance
     * @return {Ext.data.Writer} The Writer instance
     */
    getWriter: function() {
        return this.writer;
    },
    
    
/**
     * Performs the given create operation.
     * @param {Ext.data.Operation} operation The Operation to perform
     * @param {Function} callback Callback function to be called when the Operation has completed (whether successful or not)
     * @param {Object} scope Scope to execute the callback function in
     */
    create: Ext.emptyFn,
    
    
/**
     * Performs the given read operation.
     * @param {Ext.data.Operation} operation The Operation to perform
     * @param {Function} callback Callback function to be called when the Operation has completed (whether successful or not)
     * @param {Object} scope Scope to execute the callback function in
     */
    read: Ext.emptyFn,
    
    
/**
     * Performs the given update operation.
     * @param {Ext.data.Operation} operation The Operation to perform
     * @param {Function} callback Callback function to be called when the Operation has completed (whether successful or not)
     * @param {Object} scope Scope to execute the callback function in
     */
    update: Ext.emptyFn,
    
    
/**
     * Performs the given destroy operation.
     * @param {Ext.data.Operation} operation The Operation to perform
     * @param {Function} callback Callback function to be called when the Operation has completed (whether successful or not)
     * @param {Object} scope Scope to execute the callback function in
     */
    destroy: Ext.emptyFn,
    
    
/**
     * Performs a batch of {@link Ext.data.Operation Operations}, in the order specified by {@link #batchOrder}. Used internally by
     * {@link Ext.data.Store}'s {@link Ext.data.Store#sync sync} method. Example usage:
     * 

     * myProxy.batch({
     *     create : [myModel1, myModel2],
     *     update : [myModel3],
     *     destroy: [myModel4, myModel5]
     * });
     * 
     * Where the myModel* above are {@link Ext.data.Model Model} instances - in this case 1 and 2 are new instances and have not been 
     * saved before, 3 has been saved previously but needs to be updated, and 4 and 5 have already been saved but should now be destroyed.
     * @param {Object} operations Object containing the Model instances to act upon, keyed by action name
     * @param {Object} listeners Optional listeners object passed straight through to the Batch - see {@link Ext.data.Batch}
     * @return {Ext.data.Batch} The newly created Ext.data.Batch object
     */
    batch: function(operations, listeners) {
        var batch = new Ext.data.Batch({
            proxy: this,
            listeners: listeners || {}
        });
        
        Ext.each(this.batchOrder.split(','), function(action) {
            if (operations[action]) {
                batch.add(new Ext.data.Operation({
                    action : action, 
                    records: operations[action]
                }));
            }
        }, this);
        
        batch.start();
        
        return batch;
    }
});

//backwards compatibility
Ext.data.DataProxy = Ext.data.Proxy;

Ext.data.ProxyMgr.registerType('proxy', Ext.data.Proxy);