feat: added NetworkBehaviour for oth client & server communication

Engine.Systems/Network/NetworkBehaviour.cs

@@ -0,0 +1,40 @@
+using Engine.Core;
+
+namespace Engine.Systems.Network;
+
+/// <summary>
+/// Basic network behaviour that supports both client & server behaviour. Finds both 
+/// the <see cref="INetworkCommunicatorClient"/> and the <see cref="INetworkCommunicatorServer"/> 
+/// in the universe in it's first active frame. Recommended to use <see cref="ClientBehaviour"/> or <see cref="ServerBehaviour"/>
+/// <br/> 
+/// Disclaimer: It implements <see cref="IFirstFrameUpdate"/> and <see cref="ILastFrameUpdate"/> in virtual methods.
+/// </summary>
+public class NetworkBehaviour : Behaviour, IFirstFrameUpdate, ILastFrameUpdate
+{
+    protected INetworkCommunicatorServer? server = null!;
+    protected INetworkCommunicatorClient? client = null!;
+
+    protected bool IsServer { get; private set; } = false;
+    protected bool IsClient { get; private set; } = false;
+
+    public INetworkCommunicatorServer Server => server ?? throw new Core.Exceptions.NotFoundException($"Universe does not contain a {nameof(INetworkCommunicatorServer)}");
+    public INetworkCommunicatorClient Client => client ?? throw new Core.Exceptions.NotFoundException($"Universe does not contain a {nameof(INetworkCommunicatorClient)}");
+
+    public virtual void FirstActiveFrame()
+    {
+        client = Universe.FindBehaviour<INetworkCommunicatorClient>();
+        server = Universe.FindBehaviour<INetworkCommunicatorServer>();
+
+        IsServer = server is not null;
+        IsClient = client is not null;
+    }
+
+    public virtual void LastActiveFrame()
+    {
+        client = null!;
+        server = null!;
+
+        IsServer = false;
+        IsClient = false;
+    }
+}