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/*
 * Copyright (c) 2016—2021 Andrei Tomashpolskiy and individual contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package bt.peer;

import bt.event.EventSource;
import bt.metainfo.Torrent;
import bt.metainfo.TorrentId;
import bt.net.Peer;
import bt.service.IRuntimeLifecycleBinder;
import bt.torrent.TorrentRegistry;
import bt.tracker.AnnounceKey;
import bt.tracker.ITrackerService;

import java.time.Duration;
import java.util.Collection;
import java.util.Collections;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

class TrackerPeerSourceFactory implements PeerSourceFactory {

    private final ITrackerService trackerService;
    private final TorrentRegistry torrentRegistry;
    private final Duration trackerQueryInterval;
    private final Duration trackerTimeout;
    private final ConcurrentMap> peerSources;

    private final ExecutorService executor;

    public TrackerPeerSourceFactory(ITrackerService trackerService,
                                    TorrentRegistry torrentRegistry,
                                    IRuntimeLifecycleBinder lifecycleBinder,
                                    EventSource eventSource,
                                    Duration trackerQueryInterval,
                                    Duration trackerTimeout,
                                    int port) {
        this.trackerService = trackerService;
        this.torrentRegistry = torrentRegistry;
        this.trackerQueryInterval = trackerQueryInterval;
        this.trackerTimeout = trackerTimeout;
        this.peerSources = new ConcurrentHashMap<>();

        this.executor = Executors.newCachedThreadPool(new ThreadFactory() {
            final AtomicInteger i = new AtomicInteger();

            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, String.format("%d.bt.peer.tracker-peer-source-%d", port, i.incrementAndGet()));
            }
        });
        eventSource.onTorrentStopped(null, e -> peerSources.remove(e.getTorrentId()));
        lifecycleBinder.onShutdown("Shutdown tracker peer sources", executor::shutdownNow);
    }

    @Override
    public PeerSource getPeerSource(TorrentId torrentId) {
        Optional torrentOptional = torrentRegistry.getTorrent(torrentId);
        if (!torrentOptional.isPresent()) {
            // return a mock peer source instead of failing, because torrent might be being fetched at the time
            return noopSource;
        }

        Torrent torrent = torrentOptional.get();
        Optional announceKey = torrent.getAnnounceKey();
        if (!announceKey.isPresent()) {
            throw new IllegalStateException("Torrent does not have an announce key");
        }

        return getOrCreateTrackerPeerSource(torrentId, announceKey.get());
    }

    /**
     * @since 1.3
     */
    public PeerSource getPeerSource(TorrentId torrentId, AnnounceKey announceKey) {
        return getOrCreateTrackerPeerSource(torrentId, announceKey);
    }

    private TrackerPeerSource getOrCreateTrackerPeerSource(TorrentId torrentId, AnnounceKey announceKey) {
        ConcurrentMap torrentAnnouncerMap = peerSources.computeIfAbsent(torrentId,
                k -> new ConcurrentHashMap<>());
        TrackerPeerSource trackerPeerSource = torrentAnnouncerMap.computeIfAbsent(announceKey,
                k -> createTrackerPeerSource(torrentId, announceKey));
        return trackerPeerSource;
    }

    private TrackerPeerSource createTrackerPeerSource(TorrentId torrentId, AnnounceKey announceKey) {
        return new TrackerPeerSource(executor, trackerService.getTracker(announceKey), torrentId,
                trackerQueryInterval, trackerTimeout);
    }

    private static final PeerSource noopSource = new PeerSource() {
        @Override
        public boolean update() {
            return false;
        }

        @Override
        public Collection getPeers() {
            return Collections.emptyList();
        }
    };
}