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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 'use strict';
      6 
      7 /**
      8  * @fileoverview Provides the Settings object.
      9  */
     10 base.exportTo('base', function() {
     11   var storage_ = localStorage;
     12 
     13   /**
     14    * Settings is a simple wrapper around local storage, to make it easier
     15    * to test classes that have settings.
     16    *
     17    * May be called as new base.Settings() or simply base.Settings()
     18    * @constructor
     19    */
     20   function Settings() {
     21     return Settings;
     22   };
     23 
     24   /**
     25    * Get the setting with the given name.
     26    *
     27    * @param {string} key The name of the setting.
     28    * @param {string=} opt_default The default value to return if not set.
     29    * @param {string=} opt_namespace If set, the setting name will be prefixed
     30    * with this namespace, e.g. "categories.settingName". This is useful for
     31    * a set of related settings.
     32    */
     33   Settings.get = function(key, opt_default, opt_namespace) {
     34     key = Settings.namespace_(key, opt_namespace);
     35     var rawVal = storage_.getItem(key);
     36     if (rawVal === null || rawVal === undefined)
     37       return opt_default;
     38 
     39     // Old settings versions used to stringify objects instead of putting them
     40     // into JSON. If those are encountered, parse will fail. In that case,
     41     // "upgrade" the setting to the default value.
     42     try {
     43       return JSON.parse(rawVal).value;
     44     } catch (e) {
     45       storage_.removeItem(Settings.namespace_(key, opt_namespace));
     46       return opt_default;
     47     }
     48   },
     49 
     50   /**
     51    * Set the setting with the given name to the given value.
     52    *
     53    * @param {string} key The name of the setting.
     54    * @param {string} value The value of the setting.
     55    * @param {string=} opt_namespace If set, the setting name will be prefixed
     56    * with this namespace, e.g. "categories.settingName". This is useful for
     57    * a set of related settings.
     58    */
     59   Settings.set = function(key, value, opt_namespace) {
     60     if (value === undefined)
     61       throw new Error('Settings.set: value must not be undefined');
     62     var v = JSON.stringify({value: value});
     63     storage_.setItem(Settings.namespace_(key, opt_namespace), v);
     64   },
     65 
     66   /**
     67    * Return a list of all the keys, or all the keys in the given namespace
     68    * if one is provided.
     69    *
     70    * @param {string=} opt_namespace If set, only return settings which
     71    * begin with this prefix.
     72    */
     73   Settings.keys = function(opt_namespace) {
     74     var result = [];
     75     opt_namespace = opt_namespace || '';
     76     for (var i = 0; i < storage_.length; i++) {
     77       var key = storage_.key(i);
     78       if (Settings.isnamespaced_(key, opt_namespace))
     79         result.push(Settings.unnamespace_(key, opt_namespace));
     80     }
     81     return result;
     82   },
     83 
     84   Settings.isnamespaced_ = function(key, opt_namespace) {
     85     return key.indexOf(Settings.normalize_(opt_namespace)) == 0;
     86   },
     87 
     88   Settings.namespace_ = function(key, opt_namespace) {
     89     return Settings.normalize_(opt_namespace) + key;
     90   },
     91 
     92   Settings.unnamespace_ = function(key, opt_namespace) {
     93     return key.replace(Settings.normalize_(opt_namespace), '');
     94   },
     95 
     96   /**
     97    * All settings are prefixed with a global namespace to avoid collisions.
     98    * Settings may also be namespaced with an additional prefix passed into
     99    * the get, set, and keys methods in order to group related settings.
    100    * This method makes sure the two namespaces are always set properly.
    101    */
    102   Settings.normalize_ = function(opt_namespace) {
    103     return Settings.NAMESPACE + (opt_namespace ? opt_namespace + '.' : '');
    104   }
    105 
    106   Settings.setAlternativeStorageInstance = function(instance) {
    107     storage_ = instance;
    108   }
    109   Settings.getAlternativeStorageInstance = function() {
    110     if (storage_ === localStorage)
    111       return undefined;
    112     return storage_;
    113   }
    114 
    115   Settings.NAMESPACE = 'trace-viewer';
    116 
    117   return {
    118     Settings: Settings
    119   };
    120 });
    121