/**
 * @author Ed Spencer
 * @class Ext.data.WebStorageProxy
 * @extends Ext.data.ClientProxy
 * 
 * 
WebStorageProxy is simply a superclass for the {@link Ext.data.LocalStorageProxy localStorage} and 
 * {@link Ext.data.SessionStorageProxy sessionStorage} proxies. It uses the new HTML5 key/value client-side storage 
 * objects to save {@link Ext.data.Model model instances} for offline use.
 * 
 * @constructor
 * Creates the proxy, throws an error if local storage is not supported in the current browser
 * @param {Object} config Optional config object
 */
Ext.data.WebStorageProxy = Ext.extend(Ext.data.ClientProxy, {
    
/**
     * @cfg {String} id The unique ID used as the key in which all record data are stored in the local storage object
     */
    id: undefined,

    /**
     * @ignore
     */
    constructor: function(config) {
        Ext.data.WebStorageProxy.superclass.constructor.call(this, config);
        
        
/**
         * Cached map of records already retrieved by this Proxy - ensures that the same instance is always retrieved
         * @property cache
         * @type Object
         */
        this.cache = {};

        if (this.getStorageObject() == undefined) {
            throw "Local Storage is not supported in this browser, please use another type of data proxy";
        }

        //if an id is not given, try to use the store's id instead
        this.id = this.id || (this.store ? this.store.storeId : undefined);

        if (this.id == undefined) {
            throw "No unique id was provided to the local storage proxy. See Ext.data.LocalStorageProxy documentation for details";
        }

        this.initialize();
    },

    //inherit docs
    create: function(operation, callback, scope) {
        var records = operation.records,
            length  = records.length,
            ids     = this.getIds(),
            id, record, i;
        
        operation.setStarted();

        for (i = 0; i < length; i++) {
            record = records[i];

            if (record.phantom) {
                record.phantom = false;
                id = this.getNextId();
            } else {
                id = record.getId();
            }

            this.setRecord(record, id);
            ids.push(id);
        }

        this.setIds(ids);

        operation.setCompleted();
        operation.setSuccessful();

        if (typeof callback == 'function') {
            callback.call(scope || this, operation);
        }
    },

    //inherit docs
    read: function(operation, callback, scope) {
        //TODO: respect sorters, filters, start and limit options on the Operation

        var records = [],
            ids     = this.getIds(),
            length  = ids.length,
            i, recordData, record;
        
        //read a single record
        if (operation.id) {
            record = this.getRecord(operation.id);
            
            if (record) {
                records.push(record);
                operation.setSuccessful();
            }
        } else {
            for (i = 0; i < length; i++) {
                records.push(this.getRecord(ids[i]));
            }
            operation.setSuccessful();
        }
        
        operation.setCompleted();

        operation.resultSet = new Ext.data.ResultSet({
            records: records,
            total  : records.length,
            loaded : true
        });

        if (typeof callback == 'function') {
            callback.call(scope || this, operation);
        }
    },

    //inherit docs
    update: function(operation, callback, scope) {
        var records = operation.records,
            length  = records.length,
            ids     = this.getIds(),
            record, id, i;

        operation.setStarted();

        for (i = 0; i < length; i++) {
            record = records[i];
            this.setRecord(record);
            
            //we need to update the set of ids here because it's possible that a non-phantom record was added
            //to this proxy - in which case the record's id would never have been added via the normal 'create' call
            id = record.getId();
            if (id !== undefined && ids.indexOf(id) == -1) {
                ids.push(id);
            }
        }
        this.setIds(ids);

        operation.setCompleted();
        operation.setSuccessful();

        if (typeof callback == 'function') {
            callback.call(scope || this, operation);
        }
    },

    //inherit
    destroy: function(operation, callback, scope) {
        var records = operation.records,
            length  = records.length,
            ids     = this.getIds(),

            //newIds is a copy of ids, from which we remove the destroyed records
            newIds  = [].concat(ids),
            i;

        for (i = 0; i < length; i++) {
            newIds.remove(records[i].getId());
            this.removeRecord(records[i], false);
        }

        this.setIds(newIds);

        if (typeof callback == 'function') {
            callback.call(scope || this, operation);
        }
    },

    /**
     * @private
     * Fetches a model instance from the Proxy by ID. Runs each field's decode function (if present) to decode the data
     * @param {String} id The record's unique ID
     * @return {Ext.data.Model} The model instance
     */
    getRecord: function(id) {
        if (this.cache[id] == undefined) {
            var rawData = Ext.decode(this.getStorageObject().getItem(this.getRecordKey(id))),
                data    = {},
                Model   = this.model,
                fields  = Model.prototype.fields.items,
                length  = fields.length,
                i, field, name, record;

            for (i = 0; i < length; i++) {
                field = fields[i];
                name  = field.name;

                if (typeof field.decode == 'function') {
                    data[name] = field.decode(rawData[name]);
                } else {
                    data[name] = rawData[name];
                }
            }

            record = new Model(data);
            record.phantom = false;

            this.cache[id] = record;
        }
        
        return this.cache[id];
    },

    
/**
     * Saves the given record in the Proxy. Runs each field's encode function (if present) to encode the data
     * @param {Ext.data.Model} record The model instance
     * @param {String} id The id to save the record under (defaults to the value of the record's getId() function)
     */
    setRecord: function(record, id) {
        if (id) {
            record.setId(id);
        } else {
            id = record.getId();
        }

        var rawData = record.data,
            data    = {},
            model   = this.model,
            fields  = model.prototype.fields.items,
            length  = fields.length,
            i, field, name;

        for (i = 0; i < length; i++) {
            field = fields[i];
            name  = field.name;

            if (typeof field.encode == 'function') {
                data[name] = field.encode(rawData[name], record);
            } else {
                data[name] = rawData[name];
            }
        }

        var obj = this.getStorageObject(),
            key = this.getRecordKey(id);
        
        //keep the cache up to date
        this.cache[id] = record;
        
        //iPad bug requires that we remove the item before setting it
        obj.removeItem(key);
        obj.setItem(key, Ext.encode(data));
    },

    /**
     * @private
     * Physically removes a given record from the local storage. Used internally by {@link #destroy}, which you should
     * use instead because it updates the list of currently-stored record ids
     * @param {String|Number|Ext.data.Model} id The id of the record to remove, or an Ext.data.Model instance
     */
    removeRecord: function(id, updateIds) {
        if (id instanceof Ext.data.Model) {
            id = id.getId();
        }

        if (updateIds !== false) {
            var ids = this.getIds();
            ids.remove(id);
            this.setIds(ids);
        }

        this.getStorageObject().removeItem(this.getRecordKey(id));
    },

    /**
     * @private
     * Given the id of a record, returns a unique string based on that id and the id of this proxy. This is used when
     * storing data in the local storage object and should prevent naming collisions.
     * @param {String|Number|Ext.data.Model} id The record id, or a Model instance
     * @return {String} The unique key for this record
     */
    getRecordKey: function(id) {
        if (id instanceof Ext.data.Model) {
            id = id.getId();
        }

        return Ext.util.Format.format("{0}-{1}", this.id, id);
    },

    /**
     * @private
     * Returns the unique key used to store the current record counter for this proxy. This is used internally when
     * realizing models (creating them when they used to be phantoms), in order to give each model instance a unique id.
     * @return {String} The counter key
     */
    getRecordCounterKey: function() {
        return Ext.util.Format.format("{0}-counter", this.id);
    },

    /**
     * @private
     * Returns the array of record IDs stored in this Proxy
     * @return {Array} The record IDs. Each is cast as a Number
     */
    getIds: function() {
        var ids    = (this.getStorageObject().getItem(this.id) || "").split(","),
            length = ids.length,
            i;

        if (length == 1 && ids[0] == "") {
            ids = [];
        } else {
            for (i = 0; i < length; i++) {
                ids[i] = parseInt(ids[i], 10);
            }
        }

        return ids;
    },

    /**
     * @private
     * Saves the array of ids representing the set of all records in the Proxy
     * @param {Array} ids The ids to set
     */
    setIds: function(ids) {
        var obj = this.getStorageObject(),
            str = ids.join(",");
        
        obj.removeItem(this.id);
        
        if (!Ext.isEmpty(str)) {
            obj.setItem(this.id, str);
        }
    },

    /**
     * @private
     * Returns the next numerical ID that can be used when realizing a model instance (see getRecordCounterKey). Increments
     * the counter.
     * @return {Number} The id
     */
    getNextId: function() {
        var obj  = this.getStorageObject(),
            key  = this.getRecordCounterKey(),
            last = obj[key],
            ids, id;
        
        if (last == undefined) {
            ids = this.getIds();
            last = ids[ids.length - 1] || 0;
        }
        
        id = parseInt(last, 10) + 1;
        obj.setItem(key, id);
        
        return id;
    },

    /**
     * @private
     * Sets up the Proxy by claiming the key in the storage object that corresponds to the unique id of this Proxy. Called
     * automatically by the constructor, this should not need to be called again unless {@link #clear} has been called.
     */
    initialize: function() {
        var storageObject = this.getStorageObject();
        storageObject.setItem(this.id, storageObject.getItem(this.id) || "");
    },

    
/**
     * Destroys all records stored in the proxy and removes all keys and values used to support the proxy from the storage object
     */
    clear: function() {
        var obj = this.getStorageObject(),
            ids = this.getIds(),
            len = ids.length,
            i;

        //remove all the records
        for (i = 0; i < len; i++) {
            this.removeRecord(ids[i]);
        }

        //remove the supporting objects
        obj.removeItem(this.getRecordCounterKey());
        obj.removeItem(this.id);
    },

    /**
     * @private
     * Abstract function which should return the storage object that data will be saved to. This must be implemented
     * in each subclass.
     * @return {Object} The storage object
     */
    getStorageObject: function() {
        throw new Error("The getStorageObject function has not been defined in your Ext.data.WebStorageProxy subclass");
    }
});