/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.lucene.store;


import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.CountDownLatch;
import java.util.function.Consumer;

import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.SuppressForbidden;

/**
 * Simple standalone server that must be running when you
 * use {@link VerifyingLockFactory}.  This server simply
 * verifies at most one process holds the lock at a time.
 * Run without any args to see usage.
 *
 * @see VerifyingLockFactory
 * @see LockStressTest
 */

@SuppressForbidden(reason = "System.out required: command line tool")
public class LockVerifyServer {
  public static final int START_GUN_SIGNAL = 43;

  // method pkg-private for tests
  static void run(String hostname, int maxClients, Consumer<InetSocketAddress> startClients) throws Exception {
    try (final ServerSocket s = new ServerSocket()) {
      s.setReuseAddress(true);
      s.setSoTimeout(30000); // initially 30 secs to give clients enough time to startup
      s.bind(new InetSocketAddress(hostname, 0));
      final InetSocketAddress localAddr = (InetSocketAddress) s.getLocalSocketAddress();
      System.out.println("Listening on " + localAddr + "...");
      
      // callback only for the test to start the clients:
      startClients.accept(localAddr);
      
      final Object localLock = new Object();
      final int[] lockedID = new int[1];
      lockedID[0] = -1;
      final CountDownLatch startingGun = new CountDownLatch(1);
      final Thread[] threads = new Thread[maxClients];
      
      for (int count = 0; count < maxClients; count++) {
        final Socket cs = s.accept();
        threads[count] = new Thread() {
          @Override
          public void run() {
            try (InputStream in = cs.getInputStream(); OutputStream os = cs.getOutputStream()) {
              final int id = in.read();
              if (id < 0) {
                throw new IOException("Client closed connection before communication started.");
              }
              
              startingGun.await();
              os.write(START_GUN_SIGNAL);
              os.flush();
              
              while (true) {
                final int command = in.read();
                if (command < 0) {
                  return; // closed
                }
                
                synchronized (localLock) {
                  final int currentLock = lockedID[0];
                  if (currentLock == -2) {
                    return; // another thread got error, so we exit, too!
                  }
                  switch (command) {
                    case VerifyingLockFactory.MSG_LOCK_ACQUIRED:
                      // Locked
                      if (currentLock != -1) {
                        lockedID[0] = -2;
                        throw new IllegalStateException("id " + id + " got lock, but " + currentLock + " already holds the lock");
                      }
                      lockedID[0] = id;
                      break;
                    case VerifyingLockFactory.MSG_LOCK_RELEASED:
                      // Unlocked
                      if (currentLock != id) {
                        lockedID[0] = -2;
                        throw new IllegalStateException("id " + id + " released the lock, but " + currentLock + " is the one holding the lock");
                      }
                      lockedID[0] = -1;
                      break;
                    default:
                      throw new RuntimeException("Unrecognized command: " + command);
                  }
                  os.write(command);
                  os.flush();
                }
              }
            } catch (RuntimeException | Error e) {
              throw e;
            } catch (Exception ioe) {
              throw new RuntimeException(ioe);
            } finally {
              IOUtils.closeWhileHandlingException(cs);
            }
          }
        };
        threads[count].start();
      }
      
      // start
      System.out.println("All clients started, fire gun...");
      startingGun.countDown();
      
      // wait for all threads to finish
      for (Thread t : threads) {
        t.join();
      }

      System.out.println("Server terminated.");
    }
  }

  public static void main(String[] args) throws Exception {
    if (args.length != 2) {
      System.out.println("Usage: java org.apache.lucene.store.LockVerifyServer bindToIp clients\n");
      System.exit(1);
    }

    run(args[0], Integer.parseInt(args[1]), addr -> {});
  }
  
}
