Use MEF2 to load audio backends

FRESHMusicPlayer.Player/FRESHMusicPlayer.Player/Backends/AudioBackendFactory.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Composition;
+
+namespace FRESHMusicPlayer.Backends
+{
+    class AudioBackendFactory
+    {
+        [ImportMany]
+        private IEnumerable<Lazy<IAudioBackend>> backends { get; set; }
+        
+        ///<summary>
+        /// The exceptions that were raised by rejected backends.
+        ///</summary>
+        public IEnumerable<Exception> Exceptions { get; private set; } = null;
+        
+        public IAudioBackend CreateBackend(string filename)
+        {
+            var exlist = new List<Exception>();
+            Exceptions = exlist;
+            foreach (var lazybackend in backends)
+            {
+                IAudioBackend backend = null;
+                try
+                {
+                    backend = lazybackend.Value;
+                    backend.LoadSong(filename);
+                    return backend;
+                }
+                catch (Exception ex)
+                {
+                    try
+                    {
+                        backend?.Dispose();
+                    }
+                    catch
+                    {
+                    }
+                    exlist.Add(ex);
+                }
+            }
+            throw new Exception($"No backend could be found to play {filename}.\n\n{String.Join("\n\n", Exceptions)}\n");
+        }
+    }
+}
+

FRESHMusicPlayer.Player/FRESHMusicPlayer.Player/Backends/IAudioBackend.cs

@@ -8,6 +8,7 @@ namespace FRESHMusicPlayer.Backends
 {
     public interface IAudioBackend : IDisposable
     {
+        void LoadSong(string file);
         void Play();
         void Pause();
 

FRESHMusicPlayer.Player/FRESHMusicPlayer.Player/Backends/NAudioBackend.cs

@@ -1,12 +1,14 @@
 using NAudio.Wave;
 using System;
 using System.Collections.Generic;
+using System.Composition;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 
 namespace FRESHMusicPlayer.Backends
 {
+    [Export(typeof(IAudioBackend))]
     class NAudioBackend : IAudioBackend
     {
         private readonly WaveOutEvent outputDevice;
@@ -27,7 +29,7 @@ namespace FRESHMusicPlayer.Backends
         }
         public TimeSpan TotalTime => AudioFile.TotalTime; 
 
-        public NAudioBackend(string file)
+        public NAudioBackend()
         {
             if (outputDevice is null)
             {
@@ -37,12 +39,16 @@ namespace FRESHMusicPlayer.Backends
                     OnPlaybackStopped(this, new EventArgs());
                 };
             }
+        }
 
-            if (AudioFile is null)
+        public void LoadSong(string file)
+        {
+            if (AudioFile != null)
             {
-                AudioFile = new AudioFileReader(file);
-                outputDevice.Init(AudioFile);
+                AudioFile.Dispose();
             }
+            AudioFile = new AudioFileReader(file);
+            outputDevice.Init(AudioFile);
         }
 
         public void Play()

FRESHMusicPlayer.Player/FRESHMusicPlayer.Player/FRESHMusicPlayer.Core.csproj

@@ -14,6 +14,7 @@
     <PackageReference Include="Microsoft.CSharp" Version="4.7.0" />
     <PackageReference Include="NAudio" Version="1.10.0" />
     <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
+    <PackageReference Include="System.Composition" Version="1.4.1" />
     <PackageReference Include="System.Data.DataSetExtensions" Version="4.5.0" />
     <PackageReference Include="z440.atl.core" Version="3.7.0" />
   </ItemGroup>

FRESHMusicPlayer.Player/FRESHMusicPlayer.Player/Player.cs

@@ -1,6 +1,11 @@
 using DiscordRPC;
 using System;
 using System.Collections.Generic;
+using System.Composition;
+using System.Composition.Hosting;
+using System.IO;
+using System.Linq;
+using System.Reflection;
 using FRESHMusicPlayer.Handlers;
 using FRESHMusicPlayer.Utilities;
 using FRESHMusicPlayer.Backends;
@@ -39,6 +44,11 @@ namespace FRESHMusicPlayer
         public event EventHandler SongStopped;
         public event EventHandler<PlaybackExceptionEventArgs> SongException;
 
+        private CompositionHost container = new ContainerConfiguration()
+                .WithAssemblies(Directory.GetFiles(AppDomain.CurrentDomain.BaseDirectory, "*.dll")
+                    .Select(n => { try { return Assembly.LoadFile(n); } catch (Exception ex) { Console.WriteLine(ex); return null; } })
+                    .Where(a => a != null))
+                .CreateContainer();
 
         #region CoreFMP
 
@@ -120,13 +130,9 @@ namespace FRESHMusicPlayer
 
             void PMusic()
             {
-                //TODO: Check if FilePath is a file
-                //maybe we can use cd://2 for CD track 2, and anything else we can use the NAudio backend?
-
-                if (true)
-                {
-                    currentBackend = new NAudioBackend(FilePath);
-                }
+                var factory = new AudioBackendFactory();
+                container.SatisfyImports(factory);
+                currentBackend = factory.CreateBackend(FilePath);
 
                 currentBackend.Play();
                 currentBackend.Volume = CurrentVolume;