Added playing song info view and view model.

Harmonia.UI/ViewModels/PlayingSongInfoViewModel.cs

@@ -0,0 +1,91 @@
+using Avalonia.Media.Imaging;
+using Avalonia.Threading;
+using Harmonia.Core.Caching;
+using Harmonia.Core.Imaging;
+using Harmonia.Core.Models;
+using Harmonia.Core.Player;
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Harmonia.UI.ViewModels;
+
+public class PlayingSongInfoViewModel : ViewModelBase
+{
+    private readonly IAudioPlayer _audioPlayer;
+    private readonly IAudioImageCache _audioImageCache;
+
+    private CancellationTokenSource? _audioImageCancellationTokenSource;
+
+    private Song? _song;
+    public Song? Song
+    {
+        get
+        {
+            return _song;
+        }
+        private set
+        {
+            _song = value;
+            OnPropertyChanged();
+        }
+    }
+
+    private Bitmap? _songImageSource;
+    public Bitmap? SongImageSource
+    {
+        get
+        {
+            return _songImageSource;
+        }
+        private set
+        {
+            _songImageSource = value;
+            OnPropertyChanged();
+        }
+    }
+
+    public PlayingSongInfoViewModel(IAudioPlayer audioPlayer, IAudioImageCache audioImageCache)
+    {
+        _audioPlayer = audioPlayer;
+        _audioPlayer.PlayingSongChanged += OnAudioPlayerPlayingSongChanged;
+
+        _audioImageCache = audioImageCache;
+    }
+
+    private void OnAudioPlayerPlayingSongChanged(object? sender, EventArgs e)
+    {
+        Song = _audioPlayer.PlayingSong?.Song;
+        Task.Run(UpdateImage);
+    }
+
+    private async Task UpdateImage()
+    {
+        // TODO: Show default picture
+        if (Song == null)
+            return;
+
+        if (_audioImageCancellationTokenSource != null)
+            await _audioImageCancellationTokenSource.CancelAsync();
+
+        _audioImageCancellationTokenSource = new();
+        CancellationToken cancellationToken = _audioImageCancellationTokenSource.Token;
+
+        SongPictureInfo? songPictureInfo = await _audioImageCache.GetAsync(Song, cancellationToken);
+
+        if (songPictureInfo == null)
+            return;
+
+        await Dispatcher.UIThread.InvokeAsync(() => SetSongImageSource(songPictureInfo));
+    }
+
+    private void SetSongImageSource(SongPictureInfo songPictureInfo)
+    {
+        if (songPictureInfo.Data.Length == 0)
+            return;
+
+        using MemoryStream stream = new(songPictureInfo.Data);
+        SongImageSource = new(stream);
+    }
+}