using System;
using System.Diagnostics;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Threading;
using Windows.ApplicationModel.Core;
using Windows.Media.Devices;
using Windows.UI.Core;

enum HResult
{
    S_OK = 0
}

[ComImport]
[Guid("72A22D78-CDE4-431D-B8CC-843A71199B6D")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IActivateAudioInterfaceAsyncOperation
{
    void GetActivateResult([MarshalAs(UnmanagedType.Error)]out HResult activateResult, [MarshalAs(UnmanagedType.IUnknown)]out object activatedInterface);
}

[ComImport]
[Guid("41D949AB-9862-444A-80F6-C261334DA5EB")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IActivateAudioInterfaceCompletionHandler
{
    void ActivateCompleted(IActivateAudioInterfaceAsyncOperation activateOperation);
}

class ActivateAudioInterfaceCompletionHandler<T> : IActivateAudioInterfaceCompletionHandler
{
    public ActivateAudioInterfaceCompletionHandler()
    {
        m_CompletionEvent = new AutoResetEvent(false);
    }

    public void ActivateCompleted(IActivateAudioInterfaceAsyncOperation operation)
    {
        HResult operationHR;
        object activatedInterface;
        operation.GetActivateResult(out operationHR, out activatedInterface);
        Debug.Assert(operationHR == HResult.S_OK);

        m_Result = (T)activatedInterface;

        var setResult = m_CompletionEvent.Set();
        Debug.Assert(setResult != false);
    }

    public T WaitForCompletion()
    {
        var waitResult = m_CompletionEvent.WaitOne();
        Debug.Assert(waitResult != false);

        return m_Result;
    }

    private AutoResetEvent m_CompletionEvent;
    private T m_Result;
}


[ComImport]
[Guid("5CDF2C82-841E-4546-9722-0CF74078229A")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
unsafe interface IAudioEndpointVolume
{
    void RegisterControlChangeNotify(object pNotify);
    void UnregisterControlChangeNotify(object pNotify);
    uint GetChannelCount();
    void SetMasterVolumeLevel(float fLevelDB, Guid* pguidEventContext);
    void SetMasterVolumeLevelScalar(float fLevel, Guid* pguidEventContext);
    float GetMasterVolumeLevel();
    float GetMasterVolumeLevelScalar();
    void SetChannelVolumeLevel(uint nChannel, float fLevelDB, Guid* pguidEventContext);
    void SetChannelVolumeLevelScalar(uint nChannel, float fLevel, Guid* pguidEventContext);
    float GetChannelVolumeLevel(uint nChannel);
    float GetChannelVolumeLevelScalar(uint nChannel);
    void SetMute(bool bMute, Guid* pguidEventContext);
    bool GetMute();
    void GetVolumeStepInfo(out uint pnStep, out uint pnStepCount);
    void VolumeStepUp(Guid* pguidEventContext);
    void VolumeStepDown(Guid* pguidEventContext);
    uint QueryHardwareSupport();
    void GetVolumeRange(out float pflVolumeMindB, out float pflVolumeMaxdB, out float pflVolumeIncrementdB);
}

static class VolumeControl
{
    [DllImport("Mmdevapi.dll")]
    [return: MarshalAs(UnmanagedType.Error)]
    static extern HResult ActivateAudioInterfaceAsync(
        [MarshalAs(UnmanagedType.LPWStr)]string deviceInterfacePath,
        [MarshalAs(UnmanagedType.LPStruct)]Guid riid,
        IntPtr activationParams,
        IActivateAudioInterfaceCompletionHandler completionHandler,
        out IActivateAudioInterfaceAsyncOperation activationOperation);

    public static unsafe void ChangeVolumeToLevel(float level)
    {
        var defaultAudioRenderDevice = MediaDevice.GetDefaultAudioRenderId(AudioDeviceRole.Default);
        var activateAudioInterfaceCompletionHandler = new ActivateAudioInterfaceCompletionHandler<IAudioEndpointVolume>();

        IActivateAudioInterfaceAsyncOperation activateOperation;
        var hr = ActivateAudioInterfaceAsync(defaultAudioRenderDevice, typeof(IAudioEndpointVolume).GetTypeInfo().GUID, IntPtr.Zero, (IActivateAudioInterfaceCompletionHandler)activateAudioInterfaceCompletionHandler, out activateOperation);
        Debug.Assert(hr == HResult.S_OK);

        var audioEndpointVolume = activateAudioInterfaceCompletionHandler.WaitForCompletion();
        Debug.Assert(audioEndpointVolume != null);

        audioEndpointVolume.SetMasterVolumeLevelScalar(level, null);
    }
}

class FrameworkView : IFrameworkView
{
    public void Initialize(CoreApplicationView applicationView)
    {
    }

    public void SetWindow(CoreWindow window)
    {
        Debug.Assert(window != null);
        m_CoreWindow = window;
    }

    public void Load(string entryPoint)
    {
        Debug.Assert(m_CoreWindow != null);
        m_CoreWindow.Activate();
    }

    public void Run()
    {
        VolumeControl.ChangeVolumeToLevel(0.5f);
    }

    public void Uninitialize()
    {
        m_CoreWindow = null;
    }

    private ICoreWindow m_CoreWindow;
}

class FrameworkViewSource : IFrameworkViewSource
{
    public IFrameworkView CreateView()
    {
        return new FrameworkView();
    }
};

class Program
{
    static void Main()
    {
        CoreApplication.Run(new FrameworkViewSource());
    }
}