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

package com.pt.service;

import com.pt.entity.PeerInfoEntity;
import com.pt.entity.TorrentMeta;
import com.pt.exception.ResourceNotFoundException;
import com.pt.repository.PeerInfoRepository;
import com.pt.repository.TorrentMetaRepository;
import com.pt.utils.BencodeCodec;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.nio.charset.StandardCharsets;
import java.time.LocalDateTime;
import java.util.List;
import java.util.Map;

@Service
public class TrackerService {

    @Autowired
    private TorrentMetaRepository torrentMetaRepository;

    @Autowired
    private PeerInfoRepository peerInfoRepository;

    @Autowired
    private TorrentStatsService statsService;

    @Transactional
    public byte[] handleAnnounce(Map<String, String[]> params, String ipAddress) {
        try {
            // 验证必要参数
            if (!params.containsKey("info_hash") || !params.containsKey("peer_id")
                    || !params.containsKey("port")) {
                return errorResponse("Missing required parameters");
            }

            // 解析参数
            String infoHash = decodeParam(params.get("info_hash")[0]);
            String peerId = decodeParam(params.get("peer_id")[0]);
            int port = Integer.parseInt(params.get("port")[0]);

            // 获取事件类型
            String event = getEventParam(params);

            // 获取流量数据
            long uploaded = getLongParam(params, "uploaded", 0);
            long downloaded = getLongParam(params, "downloaded", 0);
            long left = getLongParam(params, "left", 0);

            // 验证种子是否存在
            TorrentMeta meta = torrentMetaRepository.findByInfoHash(infoHash);
            if (meta == null) {
                return errorResponse("Torrent not found: " + infoHash);
            }

            // 创建或更新 peer 信息
            PeerInfoEntity peer = findOrCreatePeer(peerId, infoHash);

            // 设置 peer 属性
            setPeerProperties(peer, ipAddress, port, uploaded, downloaded, left);

            // 处理事件类型
            handlePeerEvent(event, peer, left);

            // 保存 peer
            peerInfoRepository.save(peer);

            // 更新种子统计信息
            statsService.updateTorrentStats(infoHash);

            // 获取 peer 列表响应
            List<PeerInfoEntity> activePeers = peerInfoRepository.findActivePeersByInfoHash(infoHash);
            byte[] peerBytes = buildPeerResponse(activePeers);

            // 返回成功响应
            return BencodeCodec.buildTrackerResponse(1800, peerBytes);
        } catch (Exception e) {
            return errorResponse("Internal server error");
        }
    }

    // 辅助方法：获取事件参数
    private String getEventParam(Map<String, String[]> params) {
        return params.containsKey("event") ?
                decodeParam(params.get("event")[0]) : "update";
    }

    // 辅助方法：获取长整型参数
    private long getLongParam(Map<String, String[]> params, String key, long defaultValue) {
        return params.containsKey(key) ?
                Long.parseLong(params.get(key)[0]) : defaultValue;
    }

    // 辅助方法：查找或创建 peer
    private PeerInfoEntity findOrCreatePeer(String peerId, String infoHash) {
        return peerInfoRepository.findByPeerIdAndInfoHash(peerId, infoHash)
                .orElseGet(PeerInfoEntity::new);
    }

    // 辅助方法：设置 peer 属性
    private void setPeerProperties(PeerInfoEntity peer, String ip, int port,
                                   long uploaded, long downloaded, long left) {
        peer.setIp(ip);
        peer.setPort(port);
        peer.setPeerId(peer.getPeerId() != null ? peer.getPeerId() : ""); // 防止 NPE
        peer.setInfoHash(peer.getInfoHash() != null ? peer.getInfoHash() : "");
        peer.setUploaded(uploaded);
        peer.setDownloaded(downloaded);
        peer.setLeft(left);
        peer.setLastSeen(LocalDateTime.now());
    }

    // 辅助方法：处理 peer 事件
    private void handlePeerEvent(String event, PeerInfoEntity peer, long left) {
        switch (event) {
            case "started":
                peer.setStatus("downloading");
                peer.setActive(true);
                break;

            case "stopped":
                peer.setActive(false);
                break;

            case "completed":
                handleCompletedEvent(peer);
                break;

            case "update":
            default:
                handleUpdateEvent(peer, left);
                break;
        }
    }

    // 处理完成事件
    private void handleCompletedEvent(PeerInfoEntity peer) {
        peer.setStatus("completed");
        peer.setActive(true);
        peer.setLeft(0);
        incrementCompletedCount(peer.getInfoHash());
    }

    // 处理更新事件
    private void handleUpdateEvent(PeerInfoEntity peer, long left) {
        if (left == 0 && "downloading".equals(peer.getStatus())) {
            // 检测到下载完成
            peer.setStatus("completed");
            incrementCompletedCount(peer.getInfoHash());
        }
        peer.setActive(true);
    }

    // 增加完成次数
    private void incrementCompletedCount(String infoHash) {
        TorrentMeta meta = torrentMetaRepository.findByInfoHash(infoHash);
        if (meta != null) {
            statsService.incrementCompletedCount(meta.getId());
        }
    }

    // 构建 peer 响应
    private byte[] buildPeerResponse(List<PeerInfoEntity> peers) {
        List<String> ips = peers.stream().map(PeerInfoEntity::getIp).toList();
        List<Integer> ports = peers.stream().map(PeerInfoEntity::getPort).toList();
        return BencodeCodec.buildCompactPeers(ips, ports);
    }

    // 构建错误响应
    private byte[] errorResponse(String reason) {
        return BencodeCodec.encode(Map.of("failure reason", reason));
    }

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