src/main/java/com/pt/service/TrackerService.java

package com.pt.service;

import com.pt.entity.TorrentMeta;
import com.pt.repository.TorrentMetaRepository;
import com.pt.utils.BencodeCodec;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;

@Service
public class TrackerService {

    private final Map<String, List<PeerInfo>> torrentPeers = new ConcurrentHashMap<>();

    @Autowired
    private TorrentMetaRepository torrentMetaRepository;

    public byte[] handleAnnounce(Map<String, String[]> params, String ipAddress) {
        try {
            if (!params.containsKey("info_hash") || !params.containsKey("peer_id") || !params.containsKey("port")) {
                return BencodeCodec.encode(Map.of("failure reason", "Missing required parameters"));
            }

            String infoHash = decodeParam(params.get("info_hash")[0]);
            TorrentMeta meta = torrentMetaRepository.findByInfoHash(infoHash);
            if (meta == null) {
                return BencodeCodec.encode(Map.of("failure reason", "Invalid info_hash"));
            }

            String peerId = decodeParam(params.get("peer_id")[0]);
            int port = Integer.parseInt(params.get("port")[0]);

            PeerInfo peer = new PeerInfo(ipAddress, port, peerId);

            torrentPeers.computeIfAbsent(infoHash, k -> new CopyOnWriteArrayList<>());
            List<PeerInfo> peers = torrentPeers.get(infoHash);

            boolean exists = peers.stream().anyMatch(p -> p.peerId.equals(peerId));
            if (!exists) {
                peers.add(peer);
            }

            List<String> ips = peers.stream().map(p -> p.ip).toList();
            List<Integer> ports = peers.stream().map(p -> p.port).toList();
            byte[] peerBytes = BencodeCodec.buildCompactPeers(ips, ports);

            return BencodeCodec.buildTrackerResponse(1800, peerBytes);
        } catch (Exception e) {
            return BencodeCodec.encode(Map.of("failure reason", "Internal server error"));
        }
    }

    private String decodeParam(String raw) {
        return new String(raw.getBytes(StandardCharsets.ISO_8859_1), StandardCharsets.UTF_8);
    }

    private static class PeerInfo {
        String ip;
        int port;
        String peerId;

        public PeerInfo(String ip, int port, String peerId) {
            this.ip = ip;
            this.port = port;
            this.peerId = peerId;
        }
    }
}