ironbarrels/src/main/java/cpw/mods/ironchest/PacketHandler.java

package cpw.mods.ironchest;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.util.EnumMap;

import net.minecraft.network.Packet;
import net.minecraft.tileentity.TileEntity;
import net.minecraft.world.World;
import cpw.mods.fml.common.FMLCommonHandler;
import cpw.mods.fml.common.network.FMLEmbeddedChannel;
import cpw.mods.fml.common.network.FMLIndexedMessageToMessageCodec;
import cpw.mods.fml.common.network.NetworkRegistry;
import cpw.mods.fml.common.network.internal.FMLProxyPacket;
import cpw.mods.fml.relauncher.Side;
import cpw.mods.fml.relauncher.SideOnly;

/**
 * Handles the packet wrangling for IronChest
 * 
 * @author cpw
 * 
 */
public enum PacketHandler {
	INSTANCE;

	/**
	 * Our channel "pair" from {@link NetworkRegistry}
	 */
	private EnumMap<Side, FMLEmbeddedChannel> channels;

	/**
	 * Make our packet handler, and add an {@link IronChestCodec} always
	 */
	private PacketHandler() {
		// request a channel pair for IronChest from the network registry
		// Add the IronChestCodec as a member of both channel pipelines
		this.channels = NetworkRegistry.INSTANCE.newChannel("IronChest", new IronChestCodec());
		if (FMLCommonHandler.instance().getSide() == Side.CLIENT) {
			addClientHandler();
		}
	}

	/**
	 * This is only called on the client side - it adds an
	 * {@link IronChestMessageHandler} to the client side pipeline, since the
	 * only place we expect to <em>handle</em> messages is on the client.
	 */
	@SideOnly(Side.CLIENT)
	private void addClientHandler() {
		FMLEmbeddedChannel clientChannel = this.channels.get(Side.CLIENT);
		// These two lines find the existing codec (Ironchestcodec) and insert
		// our message handler after it in the pipeline
		String codec = clientChannel.findChannelHandlerNameForType(IronChestCodec.class);
		clientChannel.pipeline().addAfter(codec, "ClientHandler", new IronChestMessageHandler());
	}

	/**
	 * This class simply handles the {@link IronChestMessage} when it's received
	 * at the client side It can contain client only code, because it's only run
	 * on the client.
	 * 
	 * @author cpw
	 * 
	 */
	private static class IronChestMessageHandler extends SimpleChannelInboundHandler<IronChestMessage> {
		@Override
		protected void channelRead0(ChannelHandlerContext ctx, IronChestMessage msg) throws Exception {
			World world = IronChest.proxy.getClientWorld();
			TileEntity te = world.getTileEntity(msg.x, msg.y, msg.z);
			if (te instanceof TileEntityIronChest) {
				TileEntityIronChest icte = (TileEntityIronChest) te;
				icte.setFacing(msg.facing);
				icte.handlePacketData(msg.type, msg.items);
			}
		}
	}

	/**
	 * This is our "message". In fact, {@link FMLIndexedMessageToMessageCodec}
	 * can handle many messages on the same channel at once, using a
	 * discriminator byte. But for IronChest, we only need the one message, so
	 * we have just this.
	 * 
	 * @author cpw
	 * 
	 */
	public static class IronChestMessage {
		int x, y, z, type, facing, items[];
	}

	/**
	 * This is the codec that automatically transforms the
	 * {@link FMLProxyPacket} which wraps the client and server custom payload
	 * packets into a message we care about.
	 * 
	 * @author cpw
	 * 
	 */
	private class IronChestCodec extends FMLIndexedMessageToMessageCodec<IronChestMessage> {
		/**
		 * We register our discriminator bytes here. We only have the one type,
		 * so we only register one.
		 */
		public IronChestCodec() {
			addDiscriminator(0, IronChestMessage.class);
		}

		@Override
		public void encodeInto(ChannelHandlerContext ctx, IronChestMessage msg, ByteBuf target) throws Exception {
			target.writeInt(msg.x);
			target.writeInt(msg.y);
			target.writeInt(msg.z);
			int typeAndFacing = ((msg.type & 0x0F) | ((msg.facing & 0x0F) << 4)) & 0xFF;
			target.writeByte(typeAndFacing);
			target.writeBoolean(msg.items != null);
			if (msg.items != null) {
				int[] items = msg.items;
				for (int j = 0; j < items.length; j++) {
					int i = items[j];
					target.writeInt(i);
				}
			}
		}

		@Override
		public void decodeInto(ChannelHandlerContext ctx, ByteBuf dat, IronChestMessage msg) {
			msg.x = dat.readInt();
			msg.y = dat.readInt();
			msg.z = dat.readInt();
			int typDat = dat.readByte();
			msg.type = (byte) (typDat & 0xf);
			msg.facing = (byte) ((typDat >> 4) & 0xf);
			boolean hasStacks = dat.readBoolean();
			msg.items = new int[0];
			if (hasStacks) {
				msg.items = new int[24];
				for (int i = 0; i < msg.items.length; i++) {
					msg.items[i] = dat.readInt();
				}
			}
		}
	}

	/**
	 * This is a utility method called to transform a packet from a custom
	 * packet into a "system packet". We're called from
	 * {@link TileEntity#getDescriptionPacket()} in this case, but there are
	 * others. All network packet methods in minecraft have been adapted to
	 * handle {@link FMLProxyPacket} but general purpose objects can't be
	 * handled sadly.
	 * 
	 * This method uses the {@link IronChestCodec} to transform a custom packet
	 * {@link IronChestMessage} into an {@link FMLProxyPacket} by using the
	 * utility method {@link FMLEmbeddedChannel#generatePacketFrom(Object)} on
	 * the channel to do exactly that.
	 * 
	 * @param tileEntityIronChest
	 * @return
	 */
	public static Packet getPacket(TileEntityIronChest tileEntityIronChest) {
		IronChestMessage msg = new IronChestMessage();
		msg.x = tileEntityIronChest.xCoord;
		msg.y = tileEntityIronChest.yCoord;
		msg.z = tileEntityIronChest.zCoord;
		msg.type = tileEntityIronChest.getType().ordinal();
		msg.facing = tileEntityIronChest.getFacing();
		msg.items = tileEntityIronChest.buildIntDataList();
		return INSTANCE.channels.get(Side.SERVER).generatePacketFrom(msg);
	}
}