/*
 * (c) Copyright 2009 Talis Information Ltd.
 * All rights reserved.
 * [See end of file]
 */

package migrate.lib;

import java.nio.ByteBuffer ;
import java.util.Arrays ;

import org.openjena.atlas.lib.NotImplemented ;

/** ZigZag integers: map signed numbers onto unsigned numbers
 *  that can then be @plainlink{VarInteger} encoded.
 */
public final class ZigZagInteger
{
	/*
	  http://code.google.com/apis/protocolbuffers/docs/encoding.html
	  0 => 0
	  -1 => 1
	  1 => 2
	  etc
	  which is (32 bit)
	  (n << 1) ^ (n >> 31)
	  The >> is arthimetic shift
	  n>>32 is zero for n >= 0
	  n>>32 is all ones for n < 0
	*/

	public static byte[] encode(long value)
	{
		// TODO
	    //return null ;
	    throw new NotImplemented("ZigZagInteger.encode") ;
	}

	public static int encode(ByteBuffer bytes, long value)
	{ return -1 ; }

	public static int encode(ByteBuffer bytes, int startIdx, long value)
	{ return -1 ; }

	public static long decode(byte[] bytes, int idx)
    { return decode(ByteBuffer.wrap(bytes), idx) ; }
    
    public static long decode(ByteBuffer bytes)
    { return decode(bytes, 0) ; }
    
    public static long decode(ByteBuffer bytes, int idx)
    { return -1 ; }
	
/** Make a VarInteger from the bytes found start from idx */ 
    public static ZigZagInteger make(byte[] bytes)
    {
        return new ZigZagInteger(bytes) ;
    }
    
    private static String toString(byte[] bytes) { return toString(bytes, 0) ; }
    private static String toString(byte[] bytes, int idx)
    { return null ; }

	public static boolean equals(long value, byte[] bytes) { return equals(value, ByteBuffer.wrap(bytes)) ; }
    
    public static boolean equals(long value, ByteBuffer bytes) { return equals(value, bytes, 0) ; }
    
    public static boolean equals(long value, ByteBuffer bytes, int idx)
    {
        long x = decode(bytes, idx) ;
        return x == value ;
    }
    // ---- Factory
    
    // -- Some constants
    public static ZigZagInteger zigzag_0 = new ZigZagInteger(0) ;
    public static ZigZagInteger zigzag_1 = new ZigZagInteger(1) ;
    public static ZigZagInteger zigzag_2 = new ZigZagInteger(2) ;
    public static ZigZagInteger zigzag_minus_1 = new ZigZagInteger(-1) ;

    /** Return a ZigZagInteger that encodes the value */
    public static ZigZagInteger valueOf(long value)
    { 
        if ( value == 0 ) return zigzag_0 ;
        if ( value == 1 ) return zigzag_1 ;
        if ( value == -1 ) return zigzag_minus_1 ;
        if ( value == 2 ) return zigzag_2 ;
        return new ZigZagInteger(value) ;
    }
    
    public static int lengthOf(long value)
    {
        return calcLengthTable(value) ;
    }
    
    // ---- The object

    byte[] bytes ;
    long value = -1 ;
    
    private ZigZagInteger(long value)
    {
        if ( value < 0 )
            throw new IllegalArgumentException("Positive integers only") ;
        bytes = encode(value) ;
    }
    
    private ZigZagInteger(byte[] bytes)
    {
        if ( bytes.length == 0 )
            throw new IllegalArgumentException("Zero length byte[]") ;
        this.bytes = bytes ;
    }
    
    public int length()     { return bytes.length ; }
    public byte[] bytes()   { return bytes ; }
    
    public long value()
    { 
        if ( value == -1 )
            value = decode(bytes, 0) ;
        return value ;
    }
    
    @Override
    public int hashCode()
    { return Arrays.hashCode(bytes) ; }
    
    @Override
    public boolean equals(Object other)
    {
        if ( ! ( other instanceof ZigZagInteger ) ) return false ;
        ZigZagInteger vint = (ZigZagInteger)other ;
        return Arrays.equals(bytes, vint.bytes) ;
    }
    
    @Override
    public String toString() { return toString(bytes) ; }
    
     // Next is the impossible (it's the sign bit) 1L<<63
     static final long VarIntLengths[] = { 1L<<7 , 1L<<14 , 1L<<21 , 1L<<28 , 1L<<35, 1L<<42, 1L<<49, 1L<<56 } ;
 
     // By semi-lookup.
     private static int calcLengthTable(long value)
     {
         // Convert to VarInteger 
         value = (value << 1) ^ (value >> 63) ;
         return VarInteger.calcLengthTable(value) ;
     }
     
//     // By calculation.
//     private static int calcLength(long value)
//     {
//         int len = 1 ;   // The byte with high bit zero.
//         long N = value ;
//         byte b = 0 ;
//         while (true)
//         {
//             N >>>= 7 ;
//             if ( N == 0 )
//                 break ;
//             len ++ ;
//         }
//         return len ;
//     }
}



/*
 * (c) Copyright 2009 Talis Information Ltd.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */