chomens-bot-java/src/main/java/me/chayapak1/chomens_bot/plugins/ExtrasMessengerPlugin.java

package me.chayapak1.chomens_bot.plugins;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import me.chayapak1.chomens_bot.Bot;
import net.kyori.adventure.key.Key;
import org.geysermc.mcprotocollib.network.Session;
import org.geysermc.mcprotocollib.network.packet.Packet;
import org.geysermc.mcprotocollib.protocol.packet.common.clientbound.ClientboundCustomPayloadPacket;
import org.geysermc.mcprotocollib.protocol.packet.common.serverbound.ServerboundCustomPayloadPacket;

import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.UUID;

public class ExtrasMessengerPlugin extends Bot.Listener {
    private static final Key MINECRAFT_REGISTER_KEY = Key.key("minecraft", "register");

    private static final Key EXTRAS_REGISTER_KEY = Key.key("extras", "register");
    private static final Key EXTRAS_UNREGISTER_KEY = Key.key("extras", "unregister");
    private static final Key EXTRAS_MESSAGE_KEY = Key.key("extras", "message");

    private static final String MINECRAFT_CHANNEL_SEPARATOR = "\0";

    private static final byte END_CHAR_MASK = (byte) 0x80;

    private final List<Listener> listeners = new ArrayList<>();

    private final Bot bot;

    private final String chomens_namespace;

    public final List<String> registeredChannels = new ArrayList<>();

    public ExtrasMessengerPlugin (Bot bot) {
        this.bot = bot;
        this.chomens_namespace = bot.config.namespace + ":"; // Ex. chomens_bot: (then it will be appended by channel)

        bot.addListener(this);
    }

    @Override
    public void packetReceived (Session session, Packet packet) {
        if (packet instanceof ClientboundCustomPayloadPacket t_packet) packetReceived(t_packet);
    }

    public void packetReceived (ClientboundCustomPayloadPacket packet) {
        final Key packetChannel = packet.getChannel();

        if (packetChannel.equals(MINECRAFT_REGISTER_KEY)) {
            final String[] availableChannels = new String(packet.getData()).split(MINECRAFT_CHANNEL_SEPARATOR);

            if (
                    availableChannels.length == 0 ||
                            Arrays.stream(availableChannels).noneMatch(
                                    channel ->
                                            channel.equals(EXTRAS_REGISTER_KEY.asString()) ||
                                            channel.equals(EXTRAS_UNREGISTER_KEY.asString()) ||
                                            channel.equals(EXTRAS_MESSAGE_KEY.asString())
                            )
            ) return;

            final List<String> channels = new ArrayList<>();

            channels.add(EXTRAS_REGISTER_KEY.asString());
            channels.add(EXTRAS_UNREGISTER_KEY.asString());
            channels.add(EXTRAS_MESSAGE_KEY.asString());

            bot.session.send(
                    new ServerboundCustomPayloadPacket(
                            Key.key("minecraft", "register"),
                            String.join(MINECRAFT_CHANNEL_SEPARATOR, channels).getBytes(StandardCharsets.UTF_8)
                    )
            );

            // re-adds all the registered channels (since this minecraft register payload
            // should be emitted once we connect)
            final List<String> oldRegisteredChannels = new ArrayList<>(registeredChannels);

            registeredChannels.clear();

            for (String channel : oldRegisteredChannels) {
                registerChannel(channel);
            }
        } else if (packetChannel.equals(EXTRAS_MESSAGE_KEY)) {
            final ByteBuf buf = Unpooled.wrappedBuffer(packet.getData());

            final String channelName = readString(buf);

            if (!channelName.startsWith(chomens_namespace)) return;

            final UUID uuid = readUUID(buf);

            final byte[] data = readByteArrayToEnd(buf);

            for (Listener listener : listeners) listener.onMessage(uuid, data);
        }
    }

    public void sendPayload (String name, byte[] data) {
        final ByteBuf buf = Unpooled.buffer();

        writeString(buf, chomens_namespace + name);
        buf.writeBytes(data);

        final byte[] byteArray = readByteArrayToEnd(buf);

        bot.session.send(
                new ServerboundCustomPayloadPacket(
                        EXTRAS_MESSAGE_KEY,
                        byteArray
                )
        );
    }

    public void registerChannel (String channel) {
        final ByteBuf buf = Unpooled.buffer();

        writeString(buf, chomens_namespace + channel);

        bot.session.send(
                new ServerboundCustomPayloadPacket(
                        EXTRAS_REGISTER_KEY,
                        readByteArrayToEnd(buf)
                )
        );

        registeredChannels.add(channel);
    }

    public void unregisterChannel (String channel) {
        final boolean removed = registeredChannels.remove(channel);

        if (!removed) return;

        final ByteBuf buf = Unpooled.buffer();

        writeString(buf, chomens_namespace + channel);

        bot.session.send(
                new ServerboundCustomPayloadPacket(
                        EXTRAS_UNREGISTER_KEY,
                        readByteArrayToEnd(buf)
                )
        );
    }

    private void writeString (ByteBuf input, String string) {
        final byte[] bytesString = string.getBytes(StandardCharsets.US_ASCII);
        bytesString[bytesString.length - 1] |= END_CHAR_MASK;

        input.writeBytes(bytesString);
    }

    private String readString (ByteBuf byteBuf) {
        final byte[] buf = new byte[255];
        int idx = 0;

        for (;;) {
            final byte input = byteBuf.readByte();

            if (idx == buf.length) break;

            final boolean isLast = (input & END_CHAR_MASK) == END_CHAR_MASK;

            buf[idx++] = (byte) (input & ~END_CHAR_MASK);

            if (isLast) break;
        }

        return new String(Arrays.copyOf(buf, idx), StandardCharsets.US_ASCII);
    }

    private UUID readUUID (ByteBuf input) {
        final long mostSignificant = input.readLong();
        final long leastSignificant = input.readLong();

        return new UUID(mostSignificant, leastSignificant);
    }

    private byte[] readByteArrayToEnd (ByteBuf input) {
        final byte[] bytes = new byte[input.readableBytes()];

        input.readBytes(bytes);

        return bytes;
    }

    public void addListener (Listener listener) { listeners.add(listener); }

    public static class Listener {
        public void onMessage (UUID sender, byte[] message) {}
    }
}