Server/src/main/java/de/towerdefence/server/session/SessionsService.java

package de.towerdefence.server.session;

import de.towerdefence.server.player.Player;
import lombok.AllArgsConstructor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.concurrent.*;

@Service
@AllArgsConstructor
public class SessionsService {
    private static final int TIME_TO_LIVE_SECONDS = 30;

    private final Map<String, Channel> tokenGrants = new ConcurrentHashMap<>();
    private final Map<String, Player> sessions = new ConcurrentHashMap<>();
    private final Map<String, ScheduledFuture<?>> tokenGarbageCollectors = new ConcurrentHashMap<>();

    @Autowired
    private final JwtService jwtService;
    private static final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

    public String createSession(Player player, Channel channel){
        String jwt = jwtService.generateToken(player.getUsername(), channel, TIME_TO_LIVE_SECONDS);
        if(tokenGrants.containsKey(jwt)){
            throw new IllegalStateException("The exact same JWT allready exists");
        }
        tokenGrants.put(jwt, channel);
        sessions.put(jwt, player);
        this.tokenGarbageCollectors.put(jwt, scheduler.schedule(() -> {
            tokenGrants.remove(jwt);
            sessions.remove(jwt);
            tokenGarbageCollectors.remove(jwt);
        }, TIME_TO_LIVE_SECONDS, TimeUnit.SECONDS));
        return jwt;
    }

    public Optional<Player> getSession(String jwt, Channel channel){
        Channel grantedChannel = tokenGrants.get(jwt);
        if (grantedChannel == null || !grantedChannel.equals(channel)) {
            return Optional.empty();
        }
        Optional<String> username = jwtService.verifyToken(jwt, channel);
        if (username.isEmpty()) {
            return Optional.empty();
        }
        Player player = sessions.get(jwt);
        if (!Objects.equals(player.getUsername(), username.get())) {
            return Optional.empty();
        }
        ScheduledFuture<?> garbageCollector = tokenGarbageCollectors.get(jwt);
        if (garbageCollector != null && !garbageCollector.isCancelled() && !garbageCollector.isDone()) {
            garbageCollector.cancel(false);
        }
        tokenGarbageCollectors.remove(jwt);
        tokenGrants.remove(jwt);
        sessions.remove(jwt);
        return Optional.of(player);
    }
}