Cordova Windows plugin: Winmd + callback from JS

BatteryProxy.js

cordova.define("org.apache.cordova.battery-status.Battery", function (require, exports, module) { /*
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 *
 */

    var NOOP_TIMEOUT = 10000;
    var stopped;

    function handleResponse(successCb, errorCb, jsonResponse) {
        var info = JSON.parse(jsonResponse);

        if (info.hasOwnProperty("exceptionMessage")) {
            errorCb(info.exceptionMessage);
            return;
        }

        successCb(info, { keepCallback: true });
    }

    var Battery = {
        start: function (win, fail, args, env) {
            stopped = false;
            try {
                if (WinJS.Utilities.isPhone === true) {
                    function noop() {
                        if (stopped) {
                            return;
                        }

                        setTimeout(noop, NOOP_TIMEOUT);
                    }

                    function batteryLevelChangeCallback(jsonResult) {
                        if (stopped) {
                            return;
                        }

                        handleResponse(win, fail, jsonResult);
                    }

                    // Issue: we never get into batteryLevelChangeCallback event
                    handleResponse(win, fail, BatteryStatus.BatteryStatus.start(batteryLevelChangeCallback));

                    // So that we don't leave this module (does this impact the behavior at all?)
                    noop();
                } else {
                    fail("The operation is unsupported by this platform.");
                }
            } catch (e) {
                fail(e);
            }
        },

        stop: function () {
            stopped = true;
            BatteryStatus.BatteryStatus.stop();
        }
    };

    require("cordova/exec/proxy").add("Battery", Battery);
});

BatteryStatus.cs

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Json;
using Windows.Phone.Devices.Power;

namespace BatteryStatus
{
    public delegate void BatterStatusChangeCallback(string jsonResult);
    
    public sealed class BatteryStatus
    {
        private static Battery battery = Battery.GetDefault();
        private static BatterStatusChangeCallback _changeCallback;

        public static string Start(BatterStatusChangeCallback callback)
        {
            var currentStatus = GetBatteryStatus();

            Subscribe(callback);

            return currentStatus;
        }

        public static void Stop()
        {
            Unsubscribe();
        }

        private static void Subscribe(BatterStatusChangeCallback callback)
        {
            _changeCallback = callback;
            battery.RemainingChargePercentChanged += BatteryOnRemainingChargePercentChanged;
        }

        private static void Unsubscribe()
        {
            battery.RemainingChargePercentChanged -= BatteryOnRemainingChargePercentChanged;
            _changeCallback = null;
        }

        private static void BatteryOnRemainingChargePercentChanged(object sender, object o)
        {
            if (_changeCallback != null)
                _changeCallback(GetBatteryStatus());
        }

        public static string GetBatteryStatus()
        {
            try
            {
                return Serialize(typeof(BatteryInfo), new BatteryInfo
                {
                    Level = battery.RemainingChargePercent
                });
            }
            catch (Exception ex)
            {
                return Serialize(typeof(ExceptionInfo), new ExceptionInfo { Message = ex.Message });
            }
        }

        private static string Serialize(Type type, object obj)
        {
            using (var stream = new MemoryStream())
            {
                var jsonSer = new DataContractJsonSerializer(type);
                jsonSer.WriteObject(stream, obj);
                stream.Position = 0;
                return new StreamReader(stream).ReadToEnd();
            }
        }

        [DataContract]
        private class BatteryInfo
        {
            [DataMember(Name = "level")]
            public int Level;

            // Not supported by native API
            [DataMember(Name = "isPlugged")]
            public string IsPlugged;
        };

        [DataContract]
        private class ExceptionInfo
        {
            [DataMember(Name = "exceptionMessage")]
            public string Message = string.Empty;
        };
    }
}