McManager/src/main/java/de/ph87/mc/server/ServerService.java

package de.ph87.mc.server;

import jakarta.annotation.PostConstruct;
import lombok.NonNull;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.stereotype.Service;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;

@Slf4j
@Service
@RequiredArgsConstructor
public class ServerService {

  private final ApplicationEventPublisher applicationEventPublisher;

  private final ServerConfig serverConfig;

  private final Object serversLock = new Object();

  private List<Server> servers = new ArrayList<>();

  @PostConstruct
  public void startup() {
    final File ROOT = new File(serverConfig.getPath());
    synchronized (serversLock) {
      servers = Arrays.stream(Objects.requireNonNull(ROOT.listFiles())).map(this::_tryLoadingFromDir).filter(Optional::isPresent).map(Optional::get).toList();
    }
  }

  @NonNull
  private Optional<Server> _tryLoadingFromDir(@NonNull final File directory) {
    try {
      final Server server = new Server(directory);
      servers.stream().filter(server::eq).findFirst().ifPresent(old -> server.process = old.process);
      return Optional.of(server);
    } catch (NoMinecraftServer e) {
      log.warn(e.getMessage());
    }
    return Optional.empty();
  }

  @NonNull
  public ServerDto start(@NonNull final String name) {
    return set(name, this::start);
  }

  @NonNull
  public ServerDto stop(@NonNull final String name) {
    return set(name, this::stop);
  }

  private void start(@NonNull final Server server) {
    synchronized (server.lock) {
      if (server.isRunning()) {
        log.warn("Server is already running: name={}", server.properties.name);
        return;
      }
      stopAll();
      log.info("Starting server: name={}", server.properties.name);
      final ProcessBuilder builder = new ProcessBuilder("java", "-jar", "server.jar");
      builder.directory(server.directory);
      try {
        server.process = builder.start();
        log.info("Server started: name={}", server.properties.name);
      } catch (IOException e) {
        log.error("Failed to start Server: name={}, error={}", server.properties.name, e.getMessage());
      }
    }
  }

  private void stop(@NonNull final Server server) {
    synchronized (server.lock) {
      if (!server.isRunning()) {
        log.warn("Server is not running: name={}", server.properties.name);
        return;
      }
      if (server.shutdown) {
        log.warn("Server is already shutting down: name={}", server.properties.name);
        return;
      }
      server.shutdown = true;
      log.info("Stopping Server: name={}", server.properties.name);
      new Thread(() -> _stop_async(server), "STOP-" + server.properties.name).start();
    }
  }

  private void _stop_async(@NonNull final Server server) {
    log.debug("Thread spawned: name={}", server.properties.name);
    synchronized (server.lock) {
      assert server.process != null;
      log.info("Stopping server: name={}", server.properties.name);
      server.process.destroy();
      try {
        server.process.waitFor();
        log.info("Server stopped: name={}", server.properties.name);
      } catch (InterruptedException e) {
        log.error("Interrupted while waiting for server to stop: name={}", server.properties.name);
      } finally {
        server.process = null;
        server.shutdown = false;
        publish(server);
        log.debug("Thread terminated: name={}", server.properties.name);
      }
    }
  }

  @NonNull
  private ServerDto set(final @NonNull String name, @NonNull final Consumer<Server> modifier) {
    final Server server = getByName(name);
    modifier.accept(server);
    return publish(server);
  }

  @NonNull
  private ServerDto publish(@NonNull final Server server) {
    final ServerDto dto = new ServerDto(server);
    applicationEventPublisher.publishEvent(dto);
    return dto;
  }

  @NonNull
  private Server getByName(@NonNull final String name) {
    synchronized (serversLock) {
      return servers.stream().filter(server -> server.properties.name.equals(name)).findFirst().orElseThrow();
    }
  }

  @NonNull
  public List<ServerDto> findAll() {
    synchronized (serversLock) {
      return servers.stream().map(ServerDto::new).toList();
    }
  }

  @NonNull
  public File getIconFileByName(@NonNull final String name) {
    synchronized (serversLock) {
      return getByName(name).iconFile;
    }
  }

  @NonNull
  public List<ServerDto> stopAll() {
    synchronized (serversLock) {
      return servers.stream().peek(this::stop).map(ServerDto::new).toList();
    }
  }

}