Added logic for tags and audio engine.

Harmonia.Core/Engine/AudioPlaybackState.cs

@@ -0,0 +1,9 @@
+namespace Harmonia.Core.Engine;
+
+public enum AudioPlaybackState
+{
+    Stopped,
+    Playing,
+    Stalled,
+    Paused
+}

Harmonia.Core/Engine/IAudioEngine.cs

@@ -0,0 +1,22 @@
+namespace Harmonia.Core.Engine;
+
+public interface IAudioEngine
+{
+    string[] SupportedFormats { get; }
+    string Source { get; }
+    TimeSpan Position { get; set; }
+    TimeSpan Length { get; }
+    float Volume { get; set; }
+    bool CanPause { get; }
+    bool IsMuted { get; set; }
+    AudioPlaybackState State { get; }
+
+    Task<bool> LoadAsync(string fileName);
+    void Play();
+    void Pause();
+    void Stop();
+
+    event EventHandler<PlaybackStoppedEventArgs> PlaybackStopped;
+    event EventHandler StreamFinished;
+    event EventHandler<PlaybackStateChangedEventArgs> StateChanged;
+}

Harmonia.Core/Engine/PlaybackStateChangedEventArgs.cs

@@ -0,0 +1,7 @@
+namespace Harmonia.Core.Engine;
+
+public class PlaybackStateChangedEventArgs(AudioPlaybackState oldState, AudioPlaybackState newState) : EventArgs
+{
+    public AudioPlaybackState OldState { get; } = oldState;
+    public AudioPlaybackState State { get; } = newState;
+}

Harmonia.Core/Engine/PlaybackStoppedEventArgs.cs

@@ -0,0 +1,6 @@
+namespace Harmonia.Core.Engine;
+
+public class PlaybackStoppedEventArgs(string message) : EventArgs
+{
+    public string Message { get; } = message;
+}