From efda5ec2652bb792826b946eee14e883de3a3f26 Mon Sep 17 00:00:00 2001
From: Timothy Schenk <admin@rainote.dev>
Date: Thu, 29 Dec 2022 11:23:24 +0100
Subject: [PATCH] Implement base level packet interface

---
 Server.Packets/IPacket.cs                 |  7 ++++
 Server.Packets/PacketForwardingService.cs | 40 +++++++++++++++++++++++
 Server.Packets/PacketId.cs                |  6 ++++
 Server.Packets/PacketIdAttribute.cs       | 12 +++++++
 4 files changed, 65 insertions(+)
 create mode 100644 Server.Packets/IPacket.cs
 create mode 100644 Server.Packets/PacketForwardingService.cs
 create mode 100644 Server.Packets/PacketId.cs
 create mode 100644 Server.Packets/PacketIdAttribute.cs

diff --git a/Server.Packets/IPacket.cs b/Server.Packets/IPacket.cs
new file mode 100644
index 0000000..e424a16
--- /dev/null
+++ b/Server.Packets/IPacket.cs
@@ -0,0 +1,7 @@
+namespace Server.Packets;
+
+public interface IPacket
+{
+	Span<Byte> Serialize();
+	void Deserialize(Span<Byte> bytes);
+}
\ No newline at end of file
diff --git a/Server.Packets/PacketForwardingService.cs b/Server.Packets/PacketForwardingService.cs
new file mode 100644
index 0000000..794af3e
--- /dev/null
+++ b/Server.Packets/PacketForwardingService.cs
@@ -0,0 +1,40 @@
+using System.Collections.Immutable;
+using System.Reflection;
+
+namespace Server.Packets;
+
+public class PacketForwardingService
+{
+	private ImmutableDictionary<PacketId, System.Reflection.ConstructorInfo> _packets = null!;
+
+	public PacketForwardingService()
+	{
+		InitializePackets(typeof(IPacket).Assembly);
+	}
+
+	private void InitializePackets(Assembly assembly)
+	{
+		// Get all types that implement IPacket and have a PacketIdAttribute
+		_packets = assembly.GetTypes()
+			.Select(x => (attr: x.GetCustomAttribute<PacketIdAttribute>(), ctor: x.GetConstructor(Type.EmptyTypes)))
+			.Where(x => x.attr != null && x.ctor != null && x.GetType().IsAssignableFrom(typeof(IPacket)))
+			.ToImmutableDictionary(x => x.attr!.PacketId, x => x.ctor)!;
+	}
+
+	public IPacket Dispatch(Span<Byte> bytes)
+	{
+		// Get constructor according to packet id
+		IPacket packet = _packets[GetPacketId(bytes)].Invoke(Array.Empty<object>()) as IPacket ??
+		                 throw new InvalidOperationException();
+		// Slice off packet id
+		packet.Deserialize(bytes.Slice(2));
+		return packet;
+	}
+
+	private PacketId GetPacketId(Span<Byte> bytes)
+	{
+		PacketId id = 0;
+		id = (PacketId)BitConverter.ToUInt16(new[] { bytes[0], bytes[1] });
+		return id;
+	}
+}
\ No newline at end of file
diff --git a/Server.Packets/PacketId.cs b/Server.Packets/PacketId.cs
new file mode 100644
index 0000000..b6263a0
--- /dev/null
+++ b/Server.Packets/PacketId.cs
@@ -0,0 +1,6 @@
+namespace Server.Packets;
+
+public enum PacketId : ushort
+{
+	
+}
\ No newline at end of file
diff --git a/Server.Packets/PacketIdAttribute.cs b/Server.Packets/PacketIdAttribute.cs
new file mode 100644
index 0000000..37c8eb5
--- /dev/null
+++ b/Server.Packets/PacketIdAttribute.cs
@@ -0,0 +1,12 @@
+namespace Server.Packets;
+[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
+[JetBrains.Annotations.BaseTypeRequiredAttribute(typeof(IPacket))]
+public class PacketIdAttribute : Attribute
+{
+	public PacketIdAttribute(PacketId packetId)
+	{
+		PacketId = packetId;
+	}
+
+	public PacketId PacketId { get; private set; }
+}
\ No newline at end of file