/*
    *  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.directory.server.dns.service;
  
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Set;
  
  import org.apache.directory.server.dns.DnsException;
  import org.apache.directory.server.dns.messages.DnsMessage;
  import org.apache.directory.server.dns.messages.DnsMessageModifier;
  import org.apache.directory.server.dns.messages.MessageType;
  import org.apache.directory.server.dns.messages.OpCode;
  import org.apache.directory.server.dns.messages.QuestionRecord;
  import org.apache.directory.server.dns.messages.ResourceRecord;
  import org.apache.directory.server.dns.messages.ResponseCode;
  import org.apache.directory.server.dns.store.RecordStore;
  import org.apache.directory.server.i18n.I18n;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * Domain Name Service (DNS) Protocol (RFC 1034, 1035)
   * 
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  public final class DomainNameService
  {
      /** the log for this class */
      private static final Logger LOG = LoggerFactory.getLogger( DomainNameService.class );
  
  
      private DomainNameService()
      {
      }
  
  
      /**
       * Creates a new instance of DomainNameService.
       */
      public static void execute( DnsContext dnsContext, DnsMessage request ) throws Exception
      {
          if ( LOG.isDebugEnabled() )
          {
              monitorRequest( request );
          }
  
          getResourceRecords( dnsContext, request );
  
          if ( LOG.isDebugEnabled() )
          {
              monitorContext( dnsContext );
          }
  
          buildReply( dnsContext, request );
  
          if ( LOG.isDebugEnabled() )
          {
              monitorReply( dnsContext );
          }
      }
  
  
      private static void monitorRequest( DnsMessage request )
      {
          try
          {
              if ( LOG.isDebugEnabled() )
              {
                  LOG.debug( monitorMessage( request, "request" ) );
              }
          }
          catch ( Exception e )
          {
              // This is a monitor.  No exceptions should bubble up.
              LOG.error( I18n.err( I18n.ERR_153 ), e );
          }
      }
  
 
     private static void getResourceRecords( DnsContext dnsContext, DnsMessage request ) throws DnsException
     {
         RecordStore store = dnsContext.getStore();
 
         List<QuestionRecord> questions = request.getQuestionRecords();
 
         Iterator<QuestionRecord> it = questions.iterator();
 
         while ( it.hasNext() )
         {
             dnsContext.addResourceRecords( getEntry( store, it.next() ) );
         }
     }
 
 
     /**
      * Returns a set of {@link ResourceRecord}s from a {@link RecordStore}, given a DNS {@link QuestionRecord}.
      *
      * @param store
      * @param question
      * @return The set of {@link ResourceRecord}s.
      * @throws DNSException
      */
     private static Set<ResourceRecord> getEntry( RecordStore store, QuestionRecord question ) throws DnsException
     {
         Set<ResourceRecord> records = null;
 
         records = store.getRecords( question );
 
         if ( records == null || records.isEmpty() )
         {
             LOG.debug( "The domain name referenced in the query does not exist." );
 
             throw new DnsException( ResponseCode.NAME_ERROR );
         }
 
         return records;
     }
 
 
     private static void monitorContext( DnsContext dnsContext )
     {
         try
         {
             RecordStore store = dnsContext.getStore();
             List<ResourceRecord> records = dnsContext.getResourceRecords();
 
             StringBuilder sb = new StringBuilder();
             sb.append( "Monitoring context:" );
             sb.append( "\n\t" + "store:                     " + store );
             sb.append( "\n\t" + "records:                   " + records );
 
             LOG.debug( sb.toString() );
         }
         catch ( Exception e )
         {
             // This is a monitor.  No exceptions should bubble up.
             LOG.error( I18n.err( I18n.ERR_154 ), e );
         }
     }
 
 
     private static void buildReply( DnsContext dnsContext, DnsMessage request ) 
     {
         List<ResourceRecord> records = dnsContext.getResourceRecords();
 
         DnsMessageModifierages/DnsMessageModifier.html#DnsMessageModifier">DnsMessageModifier modifier = new DnsMessageModifier();
 
         modifier.setTransactionId( request.getTransactionId() );
         modifier.setMessageType( MessageType.RESPONSE );
         modifier.setOpCode( OpCode.QUERY );
         modifier.setAuthoritativeAnswer( false );
         modifier.setTruncated( false );
         modifier.setRecursionDesired( request.isRecursionDesired() );
         modifier.setRecursionAvailable( false );
         modifier.setReserved( false );
         modifier.setAcceptNonAuthenticatedData( false );
         modifier.setResponseCode( ResponseCode.NO_ERROR );
         modifier.setQuestionRecords( request.getQuestionRecords() );
 
         modifier.setAnswerRecords( records );
         modifier.setAuthorityRecords( new ArrayList<ResourceRecord>() );
         modifier.setAdditionalRecords( new ArrayList<ResourceRecord>() );
 
         dnsContext.setReply( modifier.getDnsMessage() );
     }
 
 
     private static void monitorReply( DnsContext dnsContext )
     {
         try
         {
             DnsMessage reply = dnsContext.getReply();
 
             if ( LOG.isDebugEnabled() )
             {
                 LOG.debug( monitorMessage( reply, "reply" ) );
             }
         }
         catch ( Exception e )
         {
             // This is a monitor.  No exceptions should bubble up.
             LOG.error( I18n.err( I18n.ERR_155 ), e );
         }
     }
 
 
     private static String monitorMessage( DnsMessage message, String direction )
     {
         MessageType messageType = message.getMessageType();
         OpCode opCode = message.getOpCode();
         ResponseCode responseCode = message.getResponseCode();
         int transactionId = message.getTransactionId();
 
         StringBuilder sb = new StringBuilder();
         sb.append( "Monitoring " + direction + ":" );
         sb.append( "\n\t" + "messageType                " + messageType );
         sb.append( "\n\t" + "opCode                     " + opCode );
         sb.append( "\n\t" + "responseCode               " + responseCode );
         sb.append( "\n\t" + "transactionId              " + transactionId );
 
         sb.append( "\n\t" + "authoritativeAnswer        " + message.isAuthoritativeAnswer() );
         sb.append( "\n\t" + "truncated                  " + message.isTruncated() );
         sb.append( "\n\t" + "recursionDesired           " + message.isRecursionDesired() );
         sb.append( "\n\t" + "recursionAvailable         " + message.isRecursionAvailable() );
         sb.append( "\n\t" + "reserved                   " + message.isReserved() );
         sb.append( "\n\t" + "acceptNonAuthenticatedData " + message.isAcceptNonAuthenticatedData() );
 
         List<QuestionRecord> questions = message.getQuestionRecords();
 
         sb.append( "\n\t" + "questions:                 " + questions );
 
         return sb.toString();
     }
 }