/*
    * 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
    *
    *      https://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.commons.net;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.net.InetAddress;
  import java.net.ServerSocket;
  import java.net.Socket;
  
  /**
   * The MockTcpServer class is a simple TCP implementation of a server for the different TCP related protocols.
   * <p>
   * To use this class simply create a new class that will extend {@link MockTcpServer} and implement
   * {@link MockTcpServer#processClientSocket(Socket)} method.
   * <p>
   * Example usage:
   * <code>
   * final class HelloWorldTCPServer extends MockTcpServer {
   *      // other fields and constructors are omitted for brevity
   *     {@literal @Override}
   *     protected void processClientSocket(final Socket clientSocket) throws Exception {
   *         try (PrintWriter pw = new PrintWriter(clientSocket.getOutputStream())) {
   *             pw.write("Hello, World!");
   *             pw.flush();
   *         }
   *     }
   * }
   * </code>
   * <p>NOTE: this is for <B>debugging and testing purposes only</B> and not meant to be run as a reliable server.</p>
   * @see org.apache.commons.net.daytime.MockDaytimeTCPServer MockDaytimeTCPServer (for example Daytime Protocol implementation)
   */
  public abstract class MockTcpServer implements Runnable, Closeable {
  
      /** Flag that indicates whether server is running */
      protected volatile boolean running;
  
      /** {@link InetAddress} on which server is bound to */
      protected final InetAddress serverAddress;
  
      /** {@link ServerSocket} on which server listens */
      protected final ServerSocket serverSocket;
  
      /** Port number on which {@link #serverSocket} is listening */
      protected final int port;
  
      /** {@link Thread} that server is running on */
      protected final Thread serverThread;
  
      /**
       * Creates new {@link MockTcpServer} that will bind to {@link InetAddress#getLocalHost()}
       * on random port.
       *
       * @throws IOException if an I/O error occurs when opening the socket.
       */
      protected MockTcpServer() throws IOException {
          this(0);
      }
  
      /**
       * Creates new {@link MockTcpServer} that will bind to {@link InetAddress#getLocalHost()}
       * on specified port.
       *
       * @param port the port number the server will bind to, or 0 to use a port number that is automatically allocated
       * @throws IOException if an I/O error occurs when opening the socket.
       */
      protected MockTcpServer(final int port) throws IOException {
          this(port, InetAddress.getLocalHost());
      }
  
      /**
       * Creates new {@link MockTcpServer} that will bind to specified {@link InetAddress} and on specified port.
       *
       * @param port the port number the server will bind to, or 0 to use a port number that is automatically allocated
       * @param serverAddress the InetAddress the server will bind to
       * @throws IOException if an I/O error occurs when opening the socket.
       */
      protected MockTcpServer(final int port, final InetAddress serverAddress) throws IOException {
          this.serverAddress = serverAddress;
          this.serverSocket = new ServerSocket(port, 50, serverAddress);
          this.port = serverSocket.getLocalPort();
          this.serverThread = new Thread(this);
      }
  
     /**
      * Closes server socket and stop listening.
      * Calling this method will have the same effect as {@link MockTcpServer#stop()}
      *
      * @throws IOException If an I/O error occurs while closing the {@link #serverSocket}.
      * @see MockTcpServer#stop()
      */
     @Override
     public void close() throws IOException {
         stop();
     }
 
     /**
      * Gets the port number on which {@link #serverSocket} is listening
      *
      * @return the port number to which this socket is listening or -1
      *         if the socket is not bound yet
      */
     public int getPort() {
         return port;
     }
 
     /**
      * Processes next client {@link Socket} from this server.
      *
      * @implNote there is no need to manually close {@code clientSocket}, it will be closed for you
      * @param clientSocket next accepted {@link Socket} you can use. Never {@code null}
      * @throws Exception in case of any error
      */
     protected abstract void processClientSocket(Socket clientSocket) throws Exception;
 
     @Override
     public final void run() {
         while (running) {
             try (Socket clientSocket = serverSocket.accept()) {
                 processClientSocket(clientSocket);
             } catch (final IOException e) {
                 System.err.println("IOException on MockWebServer serverSocket.accept(): " + e);
             } catch (final Exception e) {
                 System.err.println("MockWebServer serverSocket.accept() error: " + e);
             }
         }
     }
 
     /**
      * Starts the server and begins to listen on {@link #serverSocket}
      */
     public synchronized void start() {
         System.out.println("Starting MockWebServer...");
         if (!running) {
             running = true;
             serverThread.start();
             System.out.println("Successfully started MockWebServer on address " + serverAddress.getHostAddress() + " and port " + port);
         }
     }
 
     /**
      * Closes server socket and stop listening.
      *
      * @throws IOException If an I/O error occurs while closing the {@link #serverSocket}.
      * @see MockTcpServer#close()
      */
     public synchronized void stop() throws IOException {
         System.out.println("Closing MockWebServer...");
         if (!running) {
             return;
         }
         running = false;
         serverThread.interrupt();
         try {
             serverSocket.close();
             System.out.println("Successfully closed MockWebServer!");
         } catch (final IOException ioException) {
             System.err.println("Could not stop MockWebServer, cause: " + ioException.getMessage());
             throw ioException;
         }
     }
 
 }