src/main/java/com/example/g8backend/util/BencodeUtil.java

package com.example.g8backend.util;

import com.example.g8backend.dto.AnnounceResponseDTO;

import java.io.ByteArrayOutputStream;
import java.nio.charset.StandardCharsets;
import java.util.*;

public class BencodeUtil {
    public static byte[] encodeAnnounceResponse(AnnounceResponseDTO dto) {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        try {
            out.write('d'); // dictionary start

            writeString(out, "interval");
            writeInt(out, dto.getInterval());

            writeString(out, "peers");
            out.write('l'); // list start
            for (Map<String, Object> peer : dto.getPeers()) {
                out.write('d');
                writeString(out, "ip");
                writeString(out, (String) peer.get("ip"));
                writeString(out, "port");
                writeInt(out, ((Number) peer.get("port")).intValue());
                out.write('e');
            }
            out.write('e'); // list end

            out.write('e'); // dictionary end
        } catch (Exception e) {
            throw new RuntimeException("Bencoding failed", e);
        }
        return out.toByteArray();
    }

    private static void writeString(ByteArrayOutputStream out, String str) throws Exception {
        byte[] bytes = str.getBytes(StandardCharsets.UTF_8);
        out.write(String.valueOf(bytes.length).getBytes(StandardCharsets.UTF_8));
        out.write(':');
        out.write(bytes);
    }

    private static void writeInt(ByteArrayOutputStream out, int i) throws Exception {
        out.write('i');
        out.write(String.valueOf(i).getBytes(StandardCharsets.UTF_8));
        out.write('e');
    }
}