src/windows/BatteryStatus/BatteryStatus/BatteryStatus.cs

/*
    Licensed 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.
*/

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

namespace BatteryStatus
{
    public sealed class BatteryStatus
    {
        private static Battery battery = Battery.GetDefault();
        private static TaskCompletionSource<string> levelCompletionSource = new TaskCompletionSource<string>();

        public static string start()
        {
            battery.RemainingChargePercentChanged += BatteryOnRemainingChargePercentChanged;

            return getBatteryStatus();
        }

        public static void stop()
        {
            battery.RemainingChargePercentChanged -= BatteryOnRemainingChargePercentChanged;
        }

        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 });
            }
        }

        public static IAsyncOperation<string> getBatteryStatusChangeEvent()
        {
            return GetBatteryStatusChangeEvent().AsAsyncOperation();
        }

        private static async Task<string> GetBatteryStatusChangeEvent()
        {
            levelCompletionSource = new TaskCompletionSource<string>();

            return await levelCompletionSource.Task;
        }

        private static void BatteryOnRemainingChargePercentChanged(object sender, object o)
        {
            levelCompletionSource.SetResult(getBatteryStatus());
        }

        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;
        };
    }
}