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 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

 /* vim: set ts=2 et sw=2 tw=80 filetype=javascript: */

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 /**

  * Handles serialization of Download objects and persistence into a file, so

  * that the state of downloads can be restored across sessions.

  *

  * The file is stored in JSON format, without indentation.  With indentation

  * applied, the file would look like this:

  *

  * {

  *   "list": [

  *     {

  *       "source": "http://www.example.com/download.txt",

  *       "target": "/home/user/Downloads/download.txt"

  *     },

  *     {

  *       "source": {

  *         "url": "http://www.example.com/download.txt",

  *         "referrer": "http://www.example.com/referrer.html"

  *       },

  *       "target": "/home/user/Downloads/download-2.txt"

  *     }

  *   ]

  * }

  */

 "use strict";

 this.EXPORTED_SYMBOLS = [

   "DownloadStore",

 ];

 ////////////////////////////////////////////////////////////////////////////////

 //// Globals

 const Cc = Components.classes;

 const Ci = Components.interfaces;

 const Cu = Components.utils;

 const Cr = Components.results;

 Cu.import("resource://gre/modules/XPCOMUtils.jsm");

 XPCOMUtils.defineLazyModuleGetter(this, "Downloads",

                                   "resource://gre/modules/Downloads.jsm");

 XPCOMUtils.defineLazyModuleGetter(this, "OS",

                                   "resource://gre/modules/osfile.jsm")

 XPCOMUtils.defineLazyModuleGetter(this, "Task",

                                   "resource://gre/modules/Task.jsm");

 XPCOMUtils.defineLazyGetter(this, "gTextDecoder", function () {

   return new TextDecoder();

 });

 XPCOMUtils.defineLazyGetter(this, "gTextEncoder", function () {

   return new TextEncoder();

 });

 ////////////////////////////////////////////////////////////////////////////////

 //// DownloadStore

 /**

  * Handles serialization of Download objects and persistence into a file, so

  * that the state of downloads can be restored across sessions.

  *

  * @param aList

  *        DownloadList object to be populated or serialized.

  * @param aPath

  *        String containing the file path where data should be saved.

  */

 this.DownloadStore = function (aList, aPath)

 {

   this.list = aList;

   this.path = aPath;

 }

 this.DownloadStore.prototype = {

   /**

    * DownloadList object to be populated or serialized.

    */

   list: null,

   /**

    * String containing the file path where data should be saved.

    */

   path: "",

   /**

    * This function is called with a Download object as its first argument, and

    * should return true if the item should be saved.

    */

   onsaveitem: () => true,

   /**

    * Loads persistent downloads from the file to the list.

    *

    * @return {Promise}

    * @resolves When the operation finished successfully.

    * @rejects JavaScript exception.

    */

   load: function DS_load()

   {

     return Task.spawn(function task_DS_load() {

       let bytes;

       try {

         bytes = yield OS.File.read(this.path);

       } catch (ex if ex instanceof OS.File.Error && ex.becauseNoSuchFile) {

         // If the file does not exist, there are no downloads to load.

         return;

       }

       let storeData = JSON.parse(gTextDecoder.decode(bytes));

       // Create live downloads based on the static snapshot.

       for (let downloadData of storeData.list) {

         try {

           let download = yield Downloads.createDownload(downloadData);

           try {

             if (!download.succeeded && !download.canceled && !download.error) {

               // Try to restart the download if it was in progress during the

               // previous session.

               download.start();

             } else {

               // If the download was not in progress, try to update the current

               // progress from disk.  This is relevant in case we retained

               // partially downloaded data.

               yield download.refresh();

             }

           } finally {

             // Add the download to the list if we succeeded in creating it,

             // after we have updated its initial state.

             yield this.list.add(download);

           }

         } catch (ex) {

           // If an item is unrecognized, don't prevent others from being loaded.

           Cu.reportError(ex);

         }

       }

     }.bind(this));

   },

   /**

    * Saves persistent downloads from the list to the file.

    *

    * If an error occurs, the previous file is not deleted.

    *

    * @return {Promise}

    * @resolves When the operation finished successfully.

    * @rejects JavaScript exception.

    */

   save: function DS_save()

   {

     return Task.spawn(function task_DS_save() {

       let downloads = yield this.list.getAll();

       // Take a static snapshot of the current state of all the downloads.

       let storeData = { list: [] };

       let atLeastOneDownload = false;

       for (let download of downloads) {

         try {

           if (!this.onsaveitem(download)) {

             continue;

           }

           storeData.list.push(download.toSerializable());

           atLeastOneDownload = true;

         } catch (ex) {

           // If an item cannot be converted to a serializable form, don't

           // prevent others from being saved.

           Cu.reportError(ex);

         }

       }

       if (atLeastOneDownload) {

         // Create or overwrite the file if there are downloads to save.

         let bytes = gTextEncoder.encode(JSON.stringify(storeData));

         yield OS.File.writeAtomic(this.path, bytes,

                                   { tmpPath: this.path + ".tmp" });

       } else {

         // Remove the file if there are no downloads to save at all.

         try {

           yield OS.File.remove(this.path);

         } catch (ex if ex instanceof OS.File.Error &&

                  (ex.becauseNoSuchFile || ex.becauseAccessDenied)) {

           // On Windows, we may get an access denied error instead of a no such

           // file error if the file existed before, and was recently deleted.

         }

       }

     }.bind(this));

   },

 };