/*
    *  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.mina.util;
  
  import java.io.IOException;
  import java.net.DatagramSocket;
  import java.net.ServerSocket;
  import java.util.NoSuchElementException;
  import java.util.Set;
  import java.util.TreeSet;
  
  /**
   * Finds currently available server ports.
   *
   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
   * @see <a href="http://www.iana.org/assignments/port-numbers">IANA.org</a>
   */
  public class AvailablePortFinder {
      /**
       * The minimum number of server port number.
       */
      public static final int MIN_PORT_NUMBER = 1;
  
      /**
       * The maximum number of server port number.
       */
      public static final int MAX_PORT_NUMBER = 49151;
  
      /**
       * Creates a new instance.
       */
      private AvailablePortFinder() {
          // Do nothing
      }
  
      /**
       * @return the {@link Set} of currently available port numbers
       * ({@link Integer}).  This method is identical to
       * <code>getAvailablePorts(MIN_PORT_NUMBER, MAX_PORT_NUMBER)</code>.
       *
       * WARNING: this can take a very long time.
       */
      public static Set<Integer> getAvailablePorts() {
          return getAvailablePorts(MIN_PORT_NUMBER, MAX_PORT_NUMBER);
      }
  
      /**
       * @return an available port, selected by the system.
       *
       * @throws NoSuchElementException if there are no ports available
       */
      public static int getNextAvailable() {
          try (ServerSocket serverSocket = new ServerSocket(0)){
              // Here, we simply return an available port found by the system
              return serverSocket.getLocalPort();
          } catch (IOException ioe) {
              throw new NoSuchElementException(ioe.getMessage());
          }
      }
  
      /**
       * @return the next available port starting at a port.
       *
       * @param fromPort the port to scan for availability
       * @throws NoSuchElementException if there are no ports available
       */
      public static int getNextAvailable(int fromPort) {
          if (fromPort < MIN_PORT_NUMBER || fromPort > MAX_PORT_NUMBER) {
              throw new IllegalArgumentException("Invalid start port: " + fromPort);
          }
  
          for (int i = fromPort; i <= MAX_PORT_NUMBER; i++) {
              if (available(i)) {
                  return i;
              }
          }
  
          throw new NoSuchElementException("Could not find an available port " + "above " + fromPort);
      }
  
      /**
       * Checks to see if a specific port is available.
      *
      * @param port the port to check for availability
      * @return <tt>true</tt> if the port is available
      */
     public static boolean available(int port) {
         if (port < MIN_PORT_NUMBER || port > MAX_PORT_NUMBER) {
             throw new IllegalArgumentException("Invalid start port: " + port);
         }
 
         ServerSocket ss = null;
         DatagramSocket ds = null;
 
         try {
             ss = new ServerSocket(port);
             ss.setReuseAddress(true);
             ds = new DatagramSocket(port);
             ds.setReuseAddress(true);
             return true;
         } catch (IOException e) {
             // Do nothing
         } finally {
             if (ds != null) {
                 ds.close();
             }
 
             if (ss != null) {
                 try {
                     ss.close();
                 } catch (IOException e) {
                     /* should not be thrown */
                 }
             }
         }
 
         return false;
     }
 
     /**
      * @param fromPort The port we start from
      * @param toPort The posrt we stop at
      * @return the {@link Set} of currently avalaible port numbers ({@link Integer})
      * between the specified port range.
      *
      * @throws IllegalArgumentException if port range is not between
      * {@link #MIN_PORT_NUMBER} and {@link #MAX_PORT_NUMBER} or
      * <code>fromPort</code> if greater than <code>toPort</code>.
      */
     public static Set<Integer> getAvailablePorts(int fromPort, int toPort) {
         if (fromPort < MIN_PORT_NUMBER || toPort > MAX_PORT_NUMBER || fromPort > toPort) {
             throw new IllegalArgumentException("Invalid port range: " + fromPort + " ~ " + toPort);
         }
 
         Set<Integer> result = new TreeSet<>();
 
         for (int i = fromPort; i <= toPort; i++) {
             ServerSocket s = null;
 
             try {
                 s = new ServerSocket(i);
                 result.add(Integer.valueOf(i));
             } catch (IOException e) {
                 // Do nothing
             } finally {
                 if (s != null) {
                     try {
                         s.close();
                     } catch (IOException e) {
                         /* should not be thrown */
                     }
                 }
             }
         }
 
         return result;
     }
 }