ExtraPylons.cs

using System.IO;
using Terraria;
using Terraria.ID;
using Terraria.ModLoader;

namespace ExtraPylons
{
	public class ExtraPylons : Mod
	{
		public static ExtraPylons Instance => ModContent.GetInstance<ExtraPylons>();

		// Network opcodes
		private const byte OpRegistrySync = 1;         // Server -> Client : full registry
		private const byte OpRegistryRequest = 2;      // Client -> Server : request registry
		private const byte OpPylonChangeRequest = 3;   // Client -> Server : inform server of place/remove (delta)
		private const byte OpPylonChangeBroadcast = 4; // Server -> Client : small delta (itemType,newCount) - kept for compatibility

		public override void HandlePacket(BinaryReader reader, int whoAmI)
		{
			byte opcode = reader.ReadByte();

			// Server -> client: receive full registry
			if (opcode == OpRegistrySync)
			{
				PylonCodes.PylonsCheckList.PylonRegistry.Clear();
				ushort count = reader.ReadUInt16();
				for (int i = 0; i < count; i++)
				{
					int itemType = reader.ReadInt32();
					int tileType = reader.ReadInt32();
					int placed = reader.ReadInt32();
					string source = reader.ReadString();
					int style = reader.ReadInt32();

					PylonCodes.PylonsCheckList.PylonRegistry.RegisterPylon(itemType, tileType, source, style);
					PylonCodes.PylonsCheckList.PylonRegistry.SetPlacedInWorldAmountByItem(itemType, placed);
				}
				return;
			}

			// Client -> server: registry request
			if (opcode == OpRegistryRequest)
			{
				if (Main.netMode == NetmodeID.Server)
					SendPylonRegistry(whoAmI);
				return;
			}

			// Client -> server: place/remove notification (delta)
			if (opcode == OpPylonChangeRequest)
			{
				if (Main.netMode != NetmodeID.Server) return;

				int itemType = reader.ReadInt32();
				int delta = reader.ReadInt32();

				if (delta > 0)
					PylonCodes.PylonsCheckList.PylonRegistry.IncrementPlacedInWorldAmountByItem(itemType);
				else
					PylonCodes.PylonsCheckList.PylonRegistry.DecrementPlacedInWorldAmountByItem(itemType);

				// Broadcast authoritative full registry to all clients to keep everyone consistent.
				SendPylonRegistry();
				return;
			}

			// Server -> client: small authoritative change (kept for compatibility with other code paths)
			if (opcode == OpPylonChangeBroadcast)
			{
				if (Main.netMode == NetmodeID.MultiplayerClient)
				{
					int itemType = reader.ReadInt32();
					int newCount = reader.ReadInt32();
					PylonCodes.PylonsCheckList.PylonRegistry.SetPlacedInWorldAmountByItem(itemType, newCount);
				}
				return;
			}
		}

		/// <summary>
		/// Sends the authoritative registry to either all clients (toClient = -1) or a single client index.
		/// </summary>
		public void SendPylonRegistry(int toClient = -1)
		{
			var entries = PylonCodes.PylonsCheckList.PylonRegistry.Entries;
			var packet = GetPacket();
			packet.Write(OpRegistrySync);
			ushort count = (ushort)(entries?.Count ?? 0);
			packet.Write(count);

			if (entries != null)
			{
				foreach (var e in entries)
				{
					packet.Write(e.ItemType);
					packet.Write(e.TileType);
					packet.Write(e.PlacedInWorldAmount);
					packet.Write(e.Source ?? string.Empty);
					packet.Write(e.Style);
				}
			}

			if (toClient >= 0)
				packet.Send(toClient);
			else
				packet.Send();
		}
	}
}