Added application session services, along with initial restore and tracker implementations.

Harmonia.WinUI/Session/SessionRestorer.cs

@@ -0,0 +1,55 @@
+using Harmonia.Core.Player;
+using Harmonia.Core.Playlists;
+using System;
+using System.Linq;
+
+namespace Harmonia.WinUI.Session;
+
+public class SessionRestorer(
+    ISessionService sessionService,
+    IPlaylistManager playlistManager,
+    IAudioPlayer audioPlayer) : ISessionRestorer
+{
+    public void Restore()
+    {
+        RestorePlaylist();
+        RestoreAudioPlayer();
+    }
+
+    private void RestorePlaylist()
+    {
+        PlaylistState playlistState = sessionService.Session.Playlist;
+
+        if (string.IsNullOrWhiteSpace(playlistState.OpenPlaylistUID))
+            return;
+
+        Playlist? playlist = playlistManager.Playlists.FirstOrDefault(p => p.UID == playlistState.OpenPlaylistUID);
+
+        if (playlist is null)
+            return;
+
+        playlistManager.CurrentPlaylist = playlist;
+    }
+
+    private void RestoreAudioPlayer()
+    {
+        AudioPlayerState audioPlayerState = sessionService.Session.Player;
+
+        if (string.IsNullOrWhiteSpace(audioPlayerState.PlaylistSongUID))
+            return;
+
+        Playlist? playlist = playlistManager.FindPlaylistContaining(audioPlayerState.PlaylistSongUID);
+
+        if (playlist is null)
+            return;
+
+        PlaylistSong? song = playlist.Songs.FirstOrDefault(s => s.UID == audioPlayerState.PlaylistSongUID);
+
+        if (song is null)
+            return;
+
+        //PlaybackMode playbackMode = audioPlayerState.PlaybackState
+
+        audioPlayer.LoadAsync(song, PlaybackMode.LoadOnly);
+    }
+}