/*
 * 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.activemq.transport.amqp.client.util;

import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.UnknownHostException;
import java.util.concurrent.atomic.AtomicLong;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Generator for Globally unique Strings.
 */
public class IdGenerator {

   private static final Logger LOG = LoggerFactory.getLogger(IdGenerator.class);
   private static final String UNIQUE_STUB;
   private static int instanceCount;
   private static String hostName;
   private String seed;
   private final AtomicLong sequence = new AtomicLong(1);
   private int length;
   public static final String PROPERTY_IDGENERATOR_PORT = "activemq.idgenerator.port";

   static {
      String stub = "";
      boolean canAccessSystemProps = true;
      try {
         SecurityManager sm = System.getSecurityManager();
         if (sm != null) {
            sm.checkPropertiesAccess();
         }
      } catch (SecurityException se) {
         canAccessSystemProps = false;
      }

      if (canAccessSystemProps) {
         int idGeneratorPort = 0;
         ServerSocket ss = null;
         try {
            idGeneratorPort = Integer.parseInt(System.getProperty(PROPERTY_IDGENERATOR_PORT, "0"));
            LOG.trace("Using port {}", idGeneratorPort);
            hostName = getLocalHostName();
            ss = new ServerSocket(idGeneratorPort);
            stub = "-" + ss.getLocalPort() + "-" + System.currentTimeMillis() + "-";
            Thread.sleep(100);
         } catch (Exception e) {
            if (LOG.isTraceEnabled()) {
               LOG.trace("could not generate unique stub by using DNS and binding to local port", e);
            } else {
               LOG.warn("could not generate unique stub by using DNS and binding to local port: {} {}", e.getClass().getCanonicalName(), e.getMessage());
            }

            // Restore interrupted state so higher level code can deal with it.
            if (e instanceof InterruptedException) {
               Thread.currentThread().interrupt();
            }
         } finally {
            if (ss != null) {
               try {
                  ss.close();
               } catch (IOException ioe) {
                  if (LOG.isTraceEnabled()) {
                     LOG.trace("Closing the server socket failed", ioe);
                  } else {
                     LOG.warn("Closing the server socket failed" + " due " + ioe.getMessage());
                  }
               }
            }
         }
      }

      if (hostName == null) {
         hostName = "localhost";
      }
      hostName = sanitizeHostName(hostName);

      if (stub.length() == 0) {
         stub = "-1-" + System.currentTimeMillis() + "-";
      }
      UNIQUE_STUB = stub;
   }

   /**
    * Construct an IdGenerator
    *
    * @param prefix The prefix value that is applied to all generated IDs.
    */
   public IdGenerator(String prefix) {
      synchronized (UNIQUE_STUB) {
         this.seed = prefix + UNIQUE_STUB + (instanceCount++) + ":";
         this.length = this.seed.length() + ("" + Long.MAX_VALUE).length();
      }
   }

   public IdGenerator() {
      this("ID:" + hostName);
   }

   /**
    * As we have to find the host name as a side-affect of generating a unique stub, we allow
    * it's easy retrieval here
    *
    * @return the local host name
    */
   public static String getHostName() {
      return hostName;
   }

   /**
    * Generate a unique id
    *
    * @return a unique id
    */
   public synchronized String generateId() {
      StringBuilder sb = new StringBuilder(length);
      sb.append(seed);
      sb.append(sequence.getAndIncrement());
      return sb.toString();
   }

   public static String sanitizeHostName(String hostName) {
      boolean changed = false;

      StringBuilder sb = new StringBuilder();
      for (char ch : hostName.toCharArray()) {
         // only include ASCII chars
         if (ch < 127) {
            sb.append(ch);
         } else {
            changed = true;
         }
      }

      if (changed) {
         String newHost = sb.toString();
         LOG.info("Sanitized hostname from: {} to: {}", hostName, newHost);
         return newHost;
      } else {
         return hostName;
      }
   }

   /**
    * Generate a unique ID - that is friendly for a URL or file system
    *
    * @return a unique id
    */
   public String generateSanitizedId() {
      String result = generateId();
      result = result.replace(':', '-');
      result = result.replace('_', '-');
      result = result.replace('.', '-');
      return result;
   }

   /**
    * From a generated id - return the seed (i.e. minus the count)
    *
    * @param id the generated identifier
    * @return the seed
    */
   public static String getSeedFromId(String id) {
      String result = id;
      if (id != null) {
         int index = id.lastIndexOf(':');
         if (index > 0 && (index + 1) < id.length()) {
            result = id.substring(0, index);
         }
      }
      return result;
   }

   /**
    * From a generated id - return the generator count
    *
    * @param id The ID that will be parsed for a sequence number.
    * @return the sequence value parsed from the given ID.
    */
   public static long getSequenceFromId(String id) {
      long result = -1;
      if (id != null) {
         int index = id.lastIndexOf(':');

         if (index > 0 && (index + 1) < id.length()) {
            String numStr = id.substring(index + 1, id.length());
            result = Long.parseLong(numStr);
         }
      }
      return result;
   }

   /**
    * Does a proper compare on the Id's
    *
    * @param id1 the lhs of the comparison.
    * @param id2 the rhs of the comparison.
    * @return 0 if equal else a positive if {@literal id1 > id2} ...
    */
   public static int compare(String id1, String id2) {
      int result = -1;
      String seed1 = IdGenerator.getSeedFromId(id1);
      String seed2 = IdGenerator.getSeedFromId(id2);
      if (seed1 != null && seed2 != null) {
         result = seed1.compareTo(seed2);
         if (result == 0) {
            long count1 = IdGenerator.getSequenceFromId(id1);
            long count2 = IdGenerator.getSequenceFromId(id2);
            result = (int) (count1 - count2);
         }
      }
      return result;
   }

   /**
    * When using the {@link java.net.InetAddress#getHostName()} method in an
    * environment where neither a proper DNS lookup nor an <code>/etc/hosts</code>
    * entry exists for a given host, the following exception will be thrown:
    * <code>
    * java.net.UnknownHostException: &lt;hostname&gt;: &lt;hostname&gt;
    * at java.net.InetAddress.getLocalHost(InetAddress.java:1425)
    * ...
    * </code>
    * Instead of just throwing an UnknownHostException and giving up, this
    * method grabs a suitable hostname from the exception and prevents the
    * exception from being thrown. If a suitable hostname cannot be acquired
    * from the exception, only then is the <code>UnknownHostException</code> thrown.
    *
    * @return The hostname
    * @throws UnknownHostException if the given host cannot be looked up.
    * @see java.net.InetAddress#getLocalHost()
    * @see java.net.InetAddress#getHostName()
    */
   protected static String getLocalHostName() throws UnknownHostException {
      try {
         return InetAddress.getLocalHost().getHostName();
      } catch (UnknownHostException uhe) {
         String host = uhe.getMessage(); // host = "hostname: hostname"
         if (host != null) {
            int colon = host.indexOf(':');
            if (colon > 0) {
               return host.substring(0, colon);
            }
         }
         throw uhe;
      }
   }
}
