ng localfs service

"use strict";
define(["module", "app"], function (module, app) {
    app.lazy.service("localFS", [
        "$q",
        function ($q) {

            var fstype = LocalFileSystem.PERSISTENT;
            var path_prefix = "educlever/";
            window.requestFileSystem(fstype, 0, function gotFS(fileSystem) {
                var dataDir = fileSystem.root.getDirectory(path_prefix, {create: true});
            }, function() {
                throw "cannot-create-root-directory";
            });

            this.save = function(filename, content) {
                var defered = $q.defer();
                window.requestFileSystem(fstype, 0, function gotFS(fileSystem) {
                    fileSystem.root.getFile(
                        path_prefix + filename,
                        {create: true, exclusive: false},
                        function gotFileEntry(fileEntry) {
                            fileEntry.createWriter(function gotFileWriter(writer) {
                                writer.onwriteend = defered.resolve;
                                writer.write(content);
                            }, defered.reject);
                        }, defered.reject);
                }, defered.reject);
                return defered.promise;
            };

            this.read = function(filename) {
                var defered = $q.defer();
                window.requestFileSystem(fstype, 0, function gotFS(fileSystem) {
                    fileSystem.root.getFile(path_prefix + filename,
                        null, function gotFileEntry(fileEntry) {
                        fileEntry.file(function gotFile(file){
                            var reader = new FileReader();
                            reader.onloadend = function(evt) {
                                defered.resolve(evt.target.result);
                            };
                            reader.readAsText(file);
                        }, defered.reject);
                    }, defered.reject);
                }, defered.reject);
                return defered.promise;
            };

            this.remove = function(filename) {
                var defered = $q.defer();
                window.requestFileSystem(fstype, 0, function gotFS(fileSystem) {
                    fileSystem.root.getFile(path_prefix + filename,
                        null, function gotFileEntry(fileEntry) {
                        fileEntry.remove(defered.resolve, defered.reject);
                    }, defered.reject);
                }, defered.reject);
                return defered.promise;
            };

        }]);

return app;
});