package org.djutils.serialization;
   
   import java.io.UnsupportedEncodingException;
   import java.nio.ByteOrder;
   
   /**
    * Method to help with Little Endian / Big Endian conversions for the Sim0MQ messages. All Sim0MQ messages are encoded Big
    * Endian over the wire.
    * <p>
   * Copyright (c) 2016-2025 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://sim0mq.org/docs/current/license.html">Sim0MQ License</a>.
   * </p>
   * @author <a href="https://www.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   */
  public final class Endianness
  {
      /** Does this EndianUtil encode and decode messages in bigEndian? */
      private final boolean bigEndian;
  
      /** Is this platform bigEndian? */
      private static final boolean PLATFORM_BIG_ENDIAN = ByteOrder.nativeOrder().equals(ByteOrder.BIG_ENDIAN);
  
      /**
       * Report whether this platform is bigEndian, or littleEndian.
       * @return true if this platform is bigEndian; false if this platform is littleEndian
       */
      public static boolean isPlatformBigEndian()
      {
          return PLATFORM_BIG_ENDIAN;
      }
  
      /** Directly usable bigEndian EndianUtil. */
      public static final Endianness BIG_ENDIAN = new Endianness(true);
  
      /** Directly usable littleEndian EndianUtil. */
      public static final Endianness LITTLE_ENDIAN = new Endianness(false);
  
      /**
       * Construct an EndianUtil object with user specified endianness.
       * @param bigEndian if true encoding and decoding use big endian style; if false; encoding and decoding use little
       *            endian style
       */
      private Endianness(final boolean bigEndian)
      {
          this.bigEndian = bigEndian;
      }
  
      /**
       * Construct an EndianUtil object that uses bigEndian encoding.
       * @return EndianUtil that uses bigEndian encoding
       */
      public static Endianness bigEndian()
      {
          return BIG_ENDIAN;
      }
  
      /**
       * Construct an EndianUtil object that uses littleEndian encoding.
       * @return EndianUtil that uses littleEndian encoding
       */
      public static Endianness littleEndian()
      {
          return LITTLE_ENDIAN;
      }
  
      /**
       * Report if this EndianUtil is bigEndian.
       * @return true if this EndianUtil is bigEndian; false if this EndianUtil is littleEndian
       */
      public boolean isBigEndian()
      {
          return this.bigEndian;
      }
  
      /**
       * Decode a short.
       * @param message the ZeroMQ byte array to decode
       * @param pointer the first byte to consider
       * @return the short value
       */
      public short decodeShort(final byte[] message, final int pointer)
      {
          if (this.bigEndian)
          {
              return (short) (((message[pointer] & 0xff) << 8) | ((message[pointer + 1] & 0xff)));
          }
          else
          {
              return (short) (((message[pointer + 1] & 0xff) << 8) | ((message[pointer] & 0xff)));
          }
      }
  
      /**
       * Decode a int.
       * @param message the ZeroMQ byte array to decode
       * @param pointer the first byte to consider
       * @return the integer value
       */
      public int decodeInt(final byte[] message, final int pointer)
     {
         if (this.bigEndian)
         {
             return (((message[pointer] & 0xff) << 24) | ((message[pointer + 1] & 0xff) << 16)
                     | ((message[pointer + 2] & 0xff) << 8) | ((message[pointer + 3] & 0xff)));
         }
         else
         {
             return (((message[pointer + 3] & 0xff) << 24) | ((message[pointer + 2] & 0xff) << 16)
                     | ((message[pointer + 1] & 0xff) << 8) | ((message[pointer] & 0xff)));
         }
     }
 
     /**
      * Decode a long.
      * @param message the ZeroMQ byte array to decode
      * @param pointer the first byte to consider
      * @return the long value
      */
     public long decodeLong(final byte[] message, final int pointer)
     {
         if (this.bigEndian)
         {
             return ((((long) message[pointer]) << 56) | (((long) message[pointer + 1] & 0xff) << 48)
                     | (((long) message[pointer + 2] & 0xff) << 40) | (((long) message[pointer + 3] & 0xff) << 32)
                     | (((long) message[pointer + 4] & 0xff) << 24) | (((long) message[pointer + 5] & 0xff) << 16)
                     | (((long) message[pointer + 6] & 0xff) << 8) | (((long) message[pointer + 7] & 0xff)));
         }
         else
         {
             return ((((long) message[pointer + 7]) << 56) | (((long) message[pointer + 6] & 0xff) << 48)
                     | (((long) message[pointer + 5] & 0xff) << 40) | (((long) message[pointer + 4] & 0xff) << 32)
                     | (((long) message[pointer + 3] & 0xff) << 24) | (((long) message[pointer + 2] & 0xff) << 16)
                     | (((long) message[pointer + 1] & 0xff) << 8) | (((long) message[pointer] & 0xff)));
         }
     }
 
     /**
      * Decode a float.
      * @param message the ZeroMQ byte array to decode
      * @param pointer the first byte to consider
      * @return the float value
      */
     public float decodeFloat(final byte[] message, final int pointer)
     {
         int bits = decodeInt(message, pointer);
         return Float.intBitsToFloat(bits);
     }
 
     /**
      * Decode a double.
      * @param message the ZeroMQ byte array to decode
      * @param pointer the first byte to consider
      * @return the double value
      */
     public double decodeDouble(final byte[] message, final int pointer)
     {
         long bits = decodeLong(message, pointer);
         return Double.longBitsToDouble(bits);
     }
 
     /**
      * Decode a char (16 bits).
      * @param message the ZeroMQ byte array to decode
      * @param pointer the first byte to consider
      * @return the short value
      */
     public char decodeChar(final byte[] message, final int pointer)
     {
         return (char) decodeShort(message, pointer);
     }
 
     /**
      * Decode a String including the length int from the message byte array.
      * @param message the message byte array
      * @param pointer the start position in the array
      * @return the Java String at position pointer
      * @throws SerializationException when the bytes cannot be parsed as UTF8
      */
     public String decodeUTF8String(final byte[] message, final int pointer) throws SerializationException
     {
         int len = decodeInt(message, pointer);
         byte[] c = new byte[len];
         for (int i = 0; i < len; i++)
         {
             c[i] = message[pointer + i + 4];
         }
         try
         {
             return new String(c, "UTF-8");
         }
         catch (UnsupportedEncodingException e)
         {
             throw new SerializationException(e);
         }
     }
 
     /**
      * Decode a String including the length int from the message byte array.
      * @param message the message byte array
      * @param pointer the start position in the array
      * @return the Java String at position pointer
      */
     public String decodeUTF16String(final byte[] message, final int pointer)
     {
         int len = decodeInt(message, pointer);
         char[] c = new char[len];
         for (int i = 0; i < len; i++)
         {
             c[i] = decodeChar(message, pointer + 2 * i + 4);
         }
         return String.copyValueOf(c);
     }
 
     /**
      * Encode a short into a message buffer.
      * @param v the variable to encode
      * @param message the message buffer to encode the variable into
      * @param pointer the pointer to start writing
      * @return the new pointer after writing
      */
     public int encodeShort(final short v, final byte[] message, final int pointer)
     {
         int p = pointer;
         if (this.bigEndian)
         {
             message[p++] = (byte) (v >> 8);
             message[p++] = (byte) (v);
         }
         else
         {
             message[p++] = (byte) (v);
             message[p++] = (byte) (v >> 8);
         }
         return p;
     }
 
     /**
      * Encode a char (16 bits) into a message buffer.
      * @param v the variable to encode
      * @param message the message buffer to encode the variable into
      * @param pointer the pointer to start writing
      * @return the new pointer after writing
      */
     public int encodeChar(final char v, final byte[] message, final int pointer)
     {
         return encodeShort((short) v, message, pointer);
     }
 
     /**
      * Encode a int into a message buffer.
      * @param v the variable to encode
      * @param message the message buffer to encode the variable into
      * @param pointer the pointer to start writing
      */
     public void encodeInt(final int v, final byte[] message, final int pointer)
     {
         int p = pointer;
         if (this.bigEndian)
         {
             message[p++] = (byte) ((v >> 24) & 0xFF);
             message[p++] = (byte) ((v >> 16) & 0xFF);
             message[p++] = (byte) ((v >> 8) & 0xFF);
             message[p++] = (byte) (v & 0xFF);
         }
         else
         {
             message[p++] = (byte) (v & 0xFF);
             message[p++] = (byte) ((v >> 8) & 0xFF);
             message[p++] = (byte) ((v >> 16) & 0xFF);
             message[p++] = (byte) ((v >> 24) & 0xFF);
         }
     }
 
     /**
      * Encode a long into a message buffer.
      * @param v the variable to encode
      * @param message the message buffer to encode the variable into
      * @param pointer the pointer to start writing
      * @return the new pointer after writing
      */
     public int encodeLong(final long v, final byte[] message, final int pointer)
     {
         int p = pointer;
         if (this.bigEndian)
         {
             message[p++] = (byte) ((v >> 56) & 0xFF);
             message[p++] = (byte) ((v >> 48) & 0xFF);
             message[p++] = (byte) ((v >> 40) & 0xFF);
             message[p++] = (byte) ((v >> 32) & 0xFF);
             message[p++] = (byte) ((v >> 24) & 0xFF);
             message[p++] = (byte) ((v >> 16) & 0xFF);
             message[p++] = (byte) ((v >> 8) & 0xFF);
             message[p++] = (byte) (v & 0xFF);
         }
         else
         {
             message[p++] = (byte) (v & 0xFF);
             message[p++] = (byte) ((v >> 8) & 0xFF);
             message[p++] = (byte) ((v >> 16) & 0xFF);
             message[p++] = (byte) ((v >> 24) & 0xFF);
             message[p++] = (byte) ((v >> 32) & 0xFF);
             message[p++] = (byte) ((v >> 40) & 0xFF);
             message[p++] = (byte) ((v >> 48) & 0xFF);
             message[p++] = (byte) ((v >> 56) & 0xFF);
         }
         return p;
     }
 
     /**
      * Encode a float into a message buffer.
      * @param v the variable to encode
      * @param message the message buffer to encode the variable into
      * @param pointer the pointer to start writing
      */
     public void encodeFloat(final float v, final byte[] message, final int pointer)
     {
         int vint = Float.floatToIntBits(v);
         encodeInt(vint, message, pointer);
     }
 
     /**
      * Encode a double into a message buffer.
      * @param v the variable to encode
      * @param message the message buffer to encode the variable into
      * @param pointer the pointer to start writing
      * @return the new pointer after writing
      */
     public int encodeDouble(final double v, final byte[] message, final int pointer)
     {
         long vlong = Double.doubleToLongBits(v);
         return encodeLong(vlong, message, pointer);
     }
 
     @Override
     public String toString()
     {
         return "EndianUtil [bigEndian=" + this.bigEndian + "]";
     }
 
 }