var objectStore = (function() {

const DBNAME = 'LOCKEDCONTENT';

const DBVERSION = 1;

const STORENAMES = ['ringtones', 'wallpapers'];

var db;

function getStore(access, storeName, callback) {

if (STORENAMES.indexOf(storeName) === -1)

throw Error('unknown object store name:', storeName);

if (db) {

callback(db.transaction(storeName, access).objectStore(storeName));

}

else {

initDB(function() { getStore(access, storeName, callback); });

}

}

function initDB(callback) {

var open = indexedDB.open(DBNAME, DBVERSION);

open.onsuccess = function() {

db = open.result;

callback();

};

open.onupgradeneeded = function() {

STORENAMES.forEach(function(storeName) {

open.result.createObjectStore(storeName, {

autoIncrement: true,

keyPath: 'id'

});

});

};

open.onerror = function() {

console.error('can not open database:', open.error.name);

};

}

return {

readonly: function readonly(storeName, callback) {

getStore('readonly', storeName, callback);

},

readwrite: function readwrite(storeName, callback) {

getStore('readwrite', storeName, callback);

}

};

}());