Play some music

private async Task PlayMusic()
{
    StorageFile song = await Package.Current.InstalledLocation.GetFileAsync(@"Music\" + songs_list[song_idx]);

    // Switch from default grid to media player grid
    if(state == AssistantState.LISTENING_DEFAULT)
    {
        await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
                                 () =>
                                 {
                                     main_page.SwitchToMediaPlayerGrid();
                                 });
    }

    await ChangeMediaPlayerVolume(0.35 * 100);
    media_player.AutoPlay = true;
    media_player.SetFileSource(song);
    state = AssistantState.BACKGROUND_MEDIA_PLAYER;
}

private async Task MediaPlayerTasksList(string command)
{
    if(command == "close")
    {
        media_player.Pause();
        song_idx = 0;
        await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
                               () =>
                               {
                                   main_page.SwitchToDefaultGrid();
                               });

        state = AssistantState.BACKGROUND_DEFAULT;
    }
    else if(command == "stop")
    {
        if(media_player.CurrentState == MediaPlayerState.Paused)
            await GUIOutput("The music has already been stopped.", true);
        else
            media_player.Pause();
        state = AssistantState.BACKGROUND_MEDIA_PLAYER;
    }
    else if(command == "play")
    {
        if(media_player.CurrentState == MediaPlayerState.Playing)
            await GUIOutput("The music is already playing.", true);
        else
            media_player.Play();
        
        state = AssistantState.BACKGROUND_MEDIA_PLAYER;
    }
    else if(command == "volume up")
    {
        if(media_player_volume <= 0.8)
        {
            media_player_volume += 0.2;
            ChangeMediaPlayerVolume(media_player_volume * 100);
        }
        
        state = AssistantState.BACKGROUND_MEDIA_PLAYER;
    }
    else if(command == "volume down")
    {
        if(media_player_volume >= 0.2)
        {
            media_player_volume -= 0.2;
            ChangeMediaPlayerVolume(media_player_volume * 100);
        }
        
        state = AssistantState.BACKGROUND_MEDIA_PLAYER;
    }
    else if(command == "next song")
    {
        media_player.Pause();
        if(song_idx + 1 >= songs_list.Count)
            song_idx = 0;
        else
            song_idx++;
        await PlayMusic();
    }
    else if(command == "previous song")
    {
        media_player.Pause();
        if(song_idx - 1 < 0)
            song_idx = songs_list.Count - 1;
        else
            song_idx--;
        await PlayMusic();
    }
    else
    {
        await GUIOutput("I'm sorry, I couldn't understand.", true);
        state = AssistantState.BACKGROUND_MEDIA_PLAYER;
    }
}

private async Task CreateSongsList()
{
    StorageFolder installed_location = Package.Current.InstalledLocation;
    StorageFolder music_folder = await installed_location.GetFolderAsync(@"Music\");
    IReadOnlyList<StorageFile> files = await music_folder.GetFilesAsync();

    foreach(StorageFile file in files)
        if(file.Name.Contains(".wma") || file.Name.Contains(".mp3"))
            songs_list.Add(file.Name);
    song_idx = 0;
}

private KeyValuePair<string, string> GetSongInfos(int idx)
{
    string title, artist, temp;
    int i = songs_list[idx].LastIndexOf('.');
    temp = songs_list[idx].Remove(i);
    i = temp.LastIndexOf('-');

    if(i > 0)
    {
       title = temp.Remove(i);
       artist = temp.Remove(0, i + 1);
    }
    else
    {
        title = temp;
        artist = "";
    }
    
    return new KeyValuePair<string, string>(title, artist);
}

private void MediaPlayerMediaEnded(MediaPlayer sender, object args) { NextSong(); }

// Slider volume control
public void SetMediaPlayerVolume(double value) { media_player.Volume = value / 100.0; }

// Media player Play button control
public void MediaPlayerPlay()
{
    if(media_player.CurrentState != MediaPlayerState.Playing)
        media_player.Play();
}

// Media player Close button control
public async Task MediaPlayerClose()
{
    media_player.Pause();
    song_idx = 0;

    await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
                           () =>
                           {
                               main_page.SwitchToDefaultGrid();
                           });

    state = AssistantState.BACKGROUND_DEFAULT;
}

// Media player Stop button control
public void MediaPlayerStop()
{
    if(media_player.CurrentState == MediaPlayerState.Playing)
        media_player.Pause();
}

// Media player Next button control
public async Task NextSong()
{
    media_player.Pause();
    if(song_idx + 1 >= songs_list.Count)
        song_idx = 0;
    else
        song_idx++;
    await PlayMusic();
}

// Media player Previous button control
public async Task PreviousSong()
{
    media_player.Pause();
    if(song_idx - 1 < 0)
        song_idx = songs_list.Count - 1;
    else
        song_idx--;
    await PlayMusic();
}

private void MediaPlayerCurrentStateChanged(MediaPlayer sender, object args)
{
    if(media_player.CurrentState == MediaPlayerState.Playing)
    {
        KeyValuePair<string, string> song_infos = GetSongInfos(song_idx);
        ChangeMediaPlayerText(song_infos.Key, song_infos.Value);
    }
    else if(media_player.CurrentState == MediaPlayerState.Paused)
        ChangeMediaPlayerText("Paused", "");
    else if(media_player.CurrentState == MediaPlayerState.Buffering)
        ChangeMediaPlayerText("Loading media", "");
}