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      1 // Copyright (c) 2013 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 /**
      6  * @fileoverview Implementation of ScreenContext class: key-value storage for
      7  * values that are shared between C++ and JS sides.
      8  */
      9 cr.define('login', function() {
     10   function require(condition, message) {
     11     if (!condition) {
     12       throw Error(message);
     13     }
     14   }
     15 
     16   function checkKeyIsValid(key) {
     17     var keyType = typeof key;
     18     require(keyType === 'string', 'Invalid type of key: "' + keyType + '".');
     19   }
     20 
     21   function checkValueIsValid(value) {
     22     var valueType = typeof value;
     23     require(['string', 'boolean', 'number'].indexOf(valueType) != -1,
     24         'Invalid type of value: "' + valueType + '".');
     25   }
     26 
     27   function ScreenContext() {
     28     this.storage_ = {};
     29     this.changes_ = {};
     30   }
     31 
     32   ScreenContext.prototype = {
     33     /**
     34      * Returns stored value for |key| or |defaultValue| if key not found in
     35      * storage. Throws Error if key not found and |defaultValue| omitted.
     36      */
     37     get: function(key, defaultValue) {
     38       checkKeyIsValid(key);
     39       if (this.hasKey(key)) {
     40         return this.storage_[key];
     41       } else if (typeof defaultValue !== 'undefined') {
     42         return defaultValue;
     43       } else {
     44         throw Error('Key "' + key + '" not found.');
     45       }
     46     },
     47 
     48     /**
     49      * Sets |value| for |key|. Returns true if call changes state of context,
     50      * false otherwise.
     51      */
     52     set: function(key, value) {
     53       checkKeyIsValid(key);
     54       checkValueIsValid(value);
     55       if (this.hasKey(key) && this.storage_[key] === value)
     56         return false;
     57       this.changes_[key] = value;
     58       this.storage_[key] = value;
     59       return true;
     60     },
     61 
     62     hasKey: function(key) {
     63       checkKeyIsValid(key);
     64       return this.storage_.hasOwnProperty(key);
     65     },
     66 
     67     hasChanges: function() {
     68       return Object.keys(this.changes_).length > 0;
     69     },
     70 
     71     /**
     72      * Applies |changes| to context. Returns Array of changed keys' names.
     73      */
     74     applyChanges: function(changes) {
     75       require(!this.hasChanges(), 'Context has changes.');
     76       Object.keys(changes).forEach(function(key) {
     77         checkKeyIsValid(key);
     78         checkValueIsValid(changes[key]);
     79         this.storage_[key] = changes[key];
     80       }, this);
     81       return Object.keys(changes);
     82     },
     83 
     84     /**
     85      * Returns changes made on context since previous call.
     86      */
     87     getChangesAndReset: function() {
     88       var result = this.changes_;
     89       this.changes_ = {};
     90       return result;
     91     }
     92   };
     93 
     94   return {
     95     ScreenContext: ScreenContext
     96   };
     97 });
     98