/*
    * Copyright 2019 The Netty Project
    *
    * The Netty Project 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 io.netty.handler.codec.dns;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.handler.codec.CorruptedFrameException;
  
  import java.net.SocketAddress;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  abstract class DnsResponseDecoder<A extends SocketAddress> {
  
      private final DnsRecordDecoder recordDecoder;
  
      /**
       * Creates a new decoder with the specified {@code recordDecoder}.
       */
      DnsResponseDecoder(DnsRecordDecoder recordDecoder) {
          this.recordDecoder = checkNotNull(recordDecoder, "recordDecoder");
      }
  
      final DnsResponse decode(A sender, A recipient, ByteBuf buffer) throws Exception {
          final int id = buffer.readUnsignedShort();
  
          final int flags = buffer.readUnsignedShort();
          if (flags >> 15 == 0) {
              throw new CorruptedFrameException("not a response");
          }
  
          final DnsResponse response = newResponse(
                  sender,
                  recipient,
                  id,
                  DnsOpCode.valueOf((byte) (flags >> 11 & 0xf)), DnsResponseCode.valueOf((byte) (flags & 0xf)));
  
          response.setRecursionDesired((flags >> 8 & 1) == 1);
          response.setAuthoritativeAnswer((flags >> 10 & 1) == 1);
          response.setTruncated((flags >> 9 & 1) == 1);
          response.setRecursionAvailable((flags >> 7 & 1) == 1);
          response.setZ(flags >> 4 & 0x7);
  
          boolean success = false;
          try {
              final int questionCount = buffer.readUnsignedShort();
              final int answerCount = buffer.readUnsignedShort();
              final int authorityRecordCount = buffer.readUnsignedShort();
              final int additionalRecordCount = buffer.readUnsignedShort();
  
              decodeQuestions(response, buffer, questionCount);
              if (!decodeRecords(response, DnsSection.ANSWER, buffer, answerCount)) {
                  success = true;
                  return response;
              }
              if (!decodeRecords(response, DnsSection.AUTHORITY, buffer, authorityRecordCount)) {
                  success = true;
                  return response;
              }
  
              decodeRecords(response, DnsSection.ADDITIONAL, buffer, additionalRecordCount);
              success = true;
              return response;
          } finally {
              if (!success) {
                  response.release();
              }
          }
      }
  
      protected abstract DnsResponse newResponse(A sender, A recipient, int id,
                                                 DnsOpCode opCode, DnsResponseCode responseCode) throws Exception;
  
      private void decodeQuestions(DnsResponse response, ByteBuf buf, int questionCount) throws Exception {
          for (int i = questionCount; i > 0; i --) {
              response.addRecord(DnsSection.QUESTION, recordDecoder.decodeQuestion(buf));
          }
      }
  
      private boolean decodeRecords(
              DnsResponse response, DnsSection section, ByteBuf buf, int count) throws Exception {
          for (int i = count; i > 0; i --) {
              final DnsRecord r = recordDecoder.decodeRecord(buf);
              if (r == null) {
                  // Truncated response
                  return false;
              }
 
             response.addRecord(section, r);
         }
         return true;
     }
 }