/**
 * Copyright (c) CI Wise Inc.  All rights reserved.  http://www.ciwise.com
 * The software in this package is published under the terms of the Apache
 * version 2.0 license, a copy of which has been included with this distribution 
 * in the LICENSE.txt file.
 * 
 */ 

package com.ciwise.accounting.util;

import java.nio.charset.Charset;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;

import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;

/**
 *  @author <a href="mailto:david@ciwise.com">David L. Whitehurst</a>
 *
 */
public class CryptoUtil
{
    /**
     *
     */
    private static String	digits = "0123456789abcdef";

    /**
     *  constant UTF-8 set of characters
     */
    private static final Charset UTF8_CHARSET = Charset.forName("UTF-8");

    /**
     * This method returns a string from expected UTF-8 bytes
     * @param bytes
     * @return
     */
    public static String decodeUTF8(byte[] bytes) {
        return new String(bytes, UTF8_CHARSET);
    }

    /**
     * This method returns a byte-array
     * @param string
     * @return
     */
    public static byte[] encodeUTF8(String string) {
        return string.getBytes(UTF8_CHARSET);
    }

    /**
     * Return length many bytes of the passed in byte array as a hex string.
     *
     * @param data the bytes to be converted.
     * @param length the number of bytes in the data block to be converted.
     * @return a hex representation of length bytes of data.
     */
    public static String toHex(byte[] data, int length)
    {
        StringBuffer	buf = new StringBuffer();

        for (int i = 0; i != length; i++)
        {
            int	v = data[i] & 0xff;

            buf.append(digits.charAt(v >> 4));
            buf.append(digits.charAt(v & 0xf));
        }

        return buf.toString();
    }

    /**
     * Return the passed in byte array as a hex string.
     *
     * @param data the bytes to be converted.
     * @return a hex representation of data.
     */
    public static String toHex(byte[] data)
    {
        return toHex(data, data.length);
    }
    
    public static byte[] hexStringToByteArray(String s) {
        int len = s.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                                 + Character.digit(s.charAt(i+1), 16));
        }
        return data;
    }
    
    /**
     * Create a key for use with AES.
     * 
     * @param bitLength
     * @param random
     * @return an AES key.
     * @throws java.security.NoSuchAlgorithmException
     * @throws java.security.NoSuchProviderException
     */
    public static SecretKey createKeyForAES(
        int          bitLength,
        SecureRandom random)
        throws NoSuchAlgorithmException, NoSuchProviderException
    {
        KeyGenerator generator = KeyGenerator.getInstance("AES"); //, "BC");
        
        generator.init(256, random);
        
        return generator.generateKey();
    }
    
    /**
     * Create an IV suitable for using with AES in CTR mode.
     * <p>
     * The IV will be composed of 4 bytes of message number,
     * 4 bytes of random data, and a counter of 8 bytes.
     * 
     * @param messageNumber the number of the message.
     * @param random a source of randomness
     * @return an initialised IvParameterSpec
     */
    public static IvParameterSpec createCtrIvForAES(
        int             messageNumber,
        SecureRandom    random)
    {
        byte[]          ivBytes = new byte[16];
        
        // initially randomize
        
        random.nextBytes(ivBytes);
        
        // set the message number bytes
        
        ivBytes[0] = (byte)(messageNumber >> 24);
        ivBytes[1] = (byte)(messageNumber >> 16);
        ivBytes[2] = (byte)(messageNumber >> 8);
        ivBytes[3] = (byte)(messageNumber >> 0);
        
        // set the counter bytes to 1
        
        for (int i = 0; i != 7; i++)
        {
            ivBytes[8 + i] = 0;
        }
        
        ivBytes[15] = 1;
        
        return new IvParameterSpec(ivBytes);
    }
    
    /**
     * Convert a byte array of 8 bit characters into a String.
     * 
     * @param bytes the array containing the characters
     * @param length the number of bytes to process
     * @return a String representation of bytes
     */
    public static String toString(
        byte[] bytes,
        int    length)
    {
        char[]	chars = new char[length];
        
        for (int i = 0; i != chars.length; i++)
        {
            chars[i] = (char)(bytes[i] & 0xff);
        }
        
        return new String(chars);
    }
    
    /**
     * Convert a byte array of 8 bit characters into a String.
     * 
     * @param bytes the array containing the characters
     * @return a String representation of bytes
     */
    public static String toString(
        byte[]	bytes)
    {
        return toString(bytes, bytes.length);
    }
    
    /**
     * Convert the passed in String to a byte array by
     * taking the bottom 8 bits of each character it contains.
     * 
     * @param string the string to be converted
     * @return a byte array representation
     */
    public static byte[] toByteArray(
        String string)
    {
        byte[]	bytes = new byte[string.length()];
        char[]  chars = string.toCharArray();
        
        for (int i = 0; i != chars.length; i++)
        {
            bytes[i] = (byte)chars[i];
        }
        
        return bytes;
    }
}