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// Copyright 2011 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
/**
* @fileoverview Provides a convenient API for data with attached metadata
* persistence. You probably don't want to use this class directly as it
* does not save any metadata by itself. It only provides the necessary
* infrastructure for subclasses that need to save metadata along with
* values stored.
*
*/
goog.provide('goog.storage.RichStorage');
goog.provide('goog.storage.RichStorage.Wrapper');
goog.require('goog.storage.ErrorCode');
goog.require('goog.storage.Storage');
/**
* Provides a storage for data with attached metadata.
*
* @param {!goog.storage.mechanism.Mechanism} mechanism The underlying
* storage mechanism.
* @constructor
* @struct
* @extends {goog.storage.Storage}
*/
goog.storage.RichStorage = function(mechanism) {
goog.storage.RichStorage.base(this, 'constructor', mechanism);
};
goog.inherits(goog.storage.RichStorage, goog.storage.Storage);
/**
* Metadata key under which the actual data is stored.
*
* @type {string}
* @protected
*/
goog.storage.RichStorage.DATA_KEY = 'data';
/**
* Wraps a value so metadata can be associated with it. You probably want
* to use goog.storage.RichStorage.Wrapper.wrapIfNecessary to avoid multiple
* embeddings.
*
* @param {*} value The value to wrap.
* @constructor
* @final
*/
goog.storage.RichStorage.Wrapper = function(value) {
this[goog.storage.RichStorage.DATA_KEY] = value;
};
/**
* Convenience method for wrapping a value so metadata can be associated with
* it. No-op if the value is already wrapped or is undefined.
*
* @param {*} value The value to wrap.
* @return {(!goog.storage.RichStorage.Wrapper|undefined)} The wrapper.
*/
goog.storage.RichStorage.Wrapper.wrapIfNecessary = function(value) {
if (!goog.isDef(value) || value instanceof goog.storage.RichStorage.Wrapper) {
return /** @type {(!goog.storage.RichStorage.Wrapper|undefined)} */ (value);
}
return new goog.storage.RichStorage.Wrapper(value);
};
/**
* Unwraps a value, any metadata is discarded (not returned). You might want to
* use goog.storage.RichStorage.Wrapper.unwrapIfPossible to handle cases where
* the wrapper is missing.
*
* @param {!Object} wrapper The wrapper.
* @return {*} The wrapped value.
*/
goog.storage.RichStorage.Wrapper.unwrap = function(wrapper) {
var value = wrapper[goog.storage.RichStorage.DATA_KEY];
if (!goog.isDef(value)) {
throw goog.storage.ErrorCode.INVALID_VALUE;
}
return value;
};
/**
* Convenience method for unwrapping a value. Returns undefined if the
* wrapper is missing.
*
* @param {(!Object|undefined)} wrapper The wrapper.
* @return {*} The wrapped value or undefined.
*/
goog.storage.RichStorage.Wrapper.unwrapIfPossible = function(wrapper) {
if (!wrapper) {
return undefined;
}
return goog.storage.RichStorage.Wrapper.unwrap(wrapper);
};
/** @override */
goog.storage.RichStorage.prototype.set = function(key, value) {
goog.storage.RichStorage.base(
this, 'set', key,
goog.storage.RichStorage.Wrapper.wrapIfNecessary(value));
};
/**
* Get an item wrapper (the item and its metadata) from the storage.
*
* WARNING: This returns an Object, which once used to be
* goog.storage.RichStorage.Wrapper. This is due to the fact
* that deserialized objects lose type information and it
* is hard to do proper typecasting in JavaScript. Be sure
* you know what you are doing when using the returned value.
*
* @param {string} key The key to get.
* @return {(!Object|undefined)} The wrapper, or undefined if not found.
*/
goog.storage.RichStorage.prototype.getWrapper = function(key) {
var wrapper = goog.storage.RichStorage.superClass_.get.call(this, key);
if (!goog.isDef(wrapper) || wrapper instanceof Object) {
return /** @type {(!Object|undefined)} */ (wrapper);
}
throw goog.storage.ErrorCode.INVALID_VALUE;
};
/** @override */
goog.storage.RichStorage.prototype.get = function(key) {
return goog.storage.RichStorage.Wrapper.unwrapIfPossible(
this.getWrapper(key));
};
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