/*
    * Copyright 2012 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:
    *
    *   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 io.netty.handler.codec.socks;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.util.CharsetUtil;
  import io.netty.util.internal.StringUtil;
  
  final class SocksCommonUtils {
      public static final SocksRequest UNKNOWN_SOCKS_REQUEST = new UnknownSocksRequest();
      public static final SocksResponse UNKNOWN_SOCKS_RESPONSE = new UnknownSocksResponse();
  
      private static final int SECOND_ADDRESS_OCTET_SHIFT = 16;
      private static final int FIRST_ADDRESS_OCTET_SHIFT = 24;
      private static final int THIRD_ADDRESS_OCTET_SHIFT = 8;
      private static final int XOR_DEFAULT_VALUE = 0xff;
  
      /**
       * A constructor to stop this class being constructed.
       */
      private SocksCommonUtils() {
          // NOOP
      }
  
      public static String intToIp(int i) {
          return String.valueOf(i >> FIRST_ADDRESS_OCTET_SHIFT & XOR_DEFAULT_VALUE) + '.' +
                 (i >> SECOND_ADDRESS_OCTET_SHIFT & XOR_DEFAULT_VALUE) + '.' +
                 (i >> THIRD_ADDRESS_OCTET_SHIFT & XOR_DEFAULT_VALUE) + '.' +
                 (i & XOR_DEFAULT_VALUE);
      }
  
      private static final char[] ipv6conseqZeroFiller = {':', ':'};
      private static final char ipv6hextetSeparator = ':';
  
      /**
       * Convert numeric IPv6 to compressed format, where
       * the longest sequence of 0's (with 2 or more 0's) is replaced with "::"
       */
      public static String ipv6toCompressedForm(byte[] src) {
          assert src.length == 16;
          //Find the longest sequence of 0's
          //start of compressed region (hextet index)
          int cmprHextet = -1;
          //length of compressed region
          int cmprSize = 0;
          for (int hextet = 0; hextet < 8;) {
              int curByte = hextet * 2;
              int size = 0;
              while (curByte < src.length && src[curByte] == 0
                      && src[curByte + 1] == 0) {
                  curByte += 2;
                  size++;
              }
              if (size > cmprSize) {
                  cmprHextet = hextet;
                  cmprSize = size;
              }
              hextet = curByte / 2 + 1;
          }
          if (cmprHextet == -1 || cmprSize < 2) {
              //No compression can be applied
              return ipv6toStr(src);
          }
          StringBuilder sb = new StringBuilder(39);
          ipv6toStr(sb, src, 0, cmprHextet);
          sb.append(ipv6conseqZeroFiller);
          ipv6toStr(sb, src, cmprHextet + cmprSize, 8);
          return sb.toString();
      }
  
      /**
       * Converts numeric IPv6 to standard (non-compressed) format.
       */
      public static String ipv6toStr(byte[] src) {
          assert src.length == 16;
          StringBuilder sb = new StringBuilder(39);
          ipv6toStr(sb, src, 0, 8);
          return sb.toString();
      }
  
      private static void ipv6toStr(StringBuilder sb, byte[] src, int fromHextet, int toHextet) {
          int i;
          toHextet --;
          for (i = fromHextet; i < toHextet; i++) {
              appendHextet(sb, src, i);
              sb.append(ipv6hextetSeparator);
         }
 
         appendHextet(sb, src, i);
     }
 
     private static void appendHextet(StringBuilder sb, byte[] src, int i) {
         StringUtil.toHexString(sb, src, i << 1, 2);
     }
 
     static String readUsAscii(ByteBuf buffer, int length) {
         String s = buffer.toString(buffer.readerIndex(), length, CharsetUtil.US_ASCII);
         buffer.skipBytes(length);
         return s;
     }
 }