/*
 * j8583 A Java implementation of the ISO8583 protocol
 * Copyright (C) 2007 Enrique Zamudio Lopez
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 */
package com.solab.iso8583.util;

/** Utility class to perform HEX encoding/decoding of values.
 * @author Enrique Zamudio
 */
public final class HexCodec {

	static final char[] HEX = "0123456789ABCDEF".toCharArray();

    private HexCodec(){}

	public static String hexEncode(byte[] buffer, int start, int length) {
		if (buffer.length == 0) {
			return "";
		}
		int holder = 0;
		char[] chars = new char[length * 2];
        int pos = -1;
		for (int i = start; i < start+length; i++) {
			holder = (buffer[i] & 0xf0) >> 4;
			chars[++pos * 2] = HEX[holder];
			holder = buffer[i] & 0x0f;
			chars[(pos * 2) + 1] = HEX[holder];
		}
		return new String(chars);
	}

	public static byte[] hexDecode(String hex) {
		//A null string returns an empty array
		if (hex == null || hex.length() == 0) {
			return new byte[0];
		} else if (hex.length() < 3) {
			return new byte[]{ (byte)(Integer.parseInt(hex, 16) & 0xff) };
		}
		//Adjust accordingly for odd-length strings
		int count = hex.length();
		int nibble = 0;
		if (count % 2 != 0) {
			count++;
			nibble = 1;
		}
		byte[] buf = new byte[count / 2];
		char c = 0;
		int holder = 0;
		int pos = 0;
		for (int i = 0; i < buf.length; i++) {
		    for (int z = 0; z < 2 && pos<hex.length(); z++) {
		        c = hex.charAt(pos++);
		        if (c >= 'A' && c <= 'F') {
		            c -= 55;
		        } else if (c >= '0' && c <= '9') {
		            c -= 48;
		        } else if (c >= 'a' && c <= 'f') {
		            c -= 87;
		        }
		        if (nibble == 0) {
		            holder = c << 4;
		        } else {
		            holder |= c;
		            buf[i] = (byte)holder;
		        }
		        nibble = 1 - nibble;
		    }
		}
		return buf;
	}

}