Bug 18619: If indexedDB disabled, use in-memory db for asyncStorage.js

const {Cc, Ci, Cu, Cr} = require("chrome");

const {indexedDB} = require("sdk/indexed-db");

const Promise = require("promise");

const prefs = require("sdk/preferences/service");

// Substitute memory-only "database" when "dom.indexedDB.enabled" is false.

// Match the API and behavior of the indexedDB-based version.

const memoryDB = function () {

  let dbMap = new Map();

  return {

    getItem : k => {

      let value = dbMap.get(k);

      // Match the behavior of indexedDB-based implementation

      // when an item is not present.

      if (value === undefined) {

        value = null;

      }

      return Promise.resolve(value);

    },

    setItem : (k, v) => Promise.resolve(dbMap.set(k, v)),

    removeItem : k => Promise.resolve(dbMap.delete(k)),

    clear : () => Promise.resolve(dbMap.clear()),

    length : () => Promise.resolve(dbMap.size),

    key : n => Promise.resolve(Array.from(dbMap.keys())[n])

  };

};

module.exports = (function() {

  "use strict";

  if (!prefs.get('dom.indexedDB.enabled', true)) {

    return memoryDB();

  }

  var DBNAME = "devtools-async-storage";

  var DBVERSION = 1;

  var STORENAME = "keyvaluepairs";