ha-bridge/src/main/java/com/bwssystems/HABridge/util/HexLibrary.java

package com.bwssystems.HABridge.util;

import java.math.BigInteger;

public class HexLibrary {

    public static String byteToHex(byte num) {
        char[] hexDigits = new char[2];
        hexDigits[0] = Character.forDigit((num >> 4) & 0xF, 16);
        hexDigits[1] = Character.forDigit((num & 0xF), 16);
        return new String(hexDigits);
    }

    public static byte hexToByte(String hexString) {
        int firstDigit = toDigit(hexString.charAt(0));
        int secondDigit = toDigit(hexString.charAt(1));
        return (byte) ((firstDigit << 4) + secondDigit);
    }

    private static int toDigit(char hexChar) {
        int digit = Character.digit(hexChar, 16);
        if (digit == -1) {
            throw new IllegalArgumentException("Invalid Hexadecimal Character: " + hexChar);
        }
        return digit;
    }

    public static String encodeHexString(byte[] byteArray) {
        StringBuffer hexStringBuffer = new StringBuffer();
        for (int i = 0; i < byteArray.length; i++) {
            hexStringBuffer.append(byteToHex(byteArray[i]));
        }
        return hexStringBuffer.toString();
    }

    public static byte[] decodeHexString(String hexString) {
        if (hexString.length() % 2 == 1) {
            throw new IllegalArgumentException("Invalid hexadecimal String supplied.");
        }

        byte[] bytes = new byte[hexString.length() / 2];
        for (int i = 0; i < hexString.length(); i += 2) {
            bytes[i / 2] = hexToByte(hexString.substring(i, i + 2));
        }
        return bytes;
    }

    public static String encodeUsingBigIntegerStringFormat(byte[] bytes) {
        BigInteger bigInteger = new BigInteger(1, bytes);
        return String.format("%0" + (bytes.length << 1) + "x", bigInteger);
    }

    public static String encodeUsingBigIntegerToString(String intValue) {
        BigInteger bigInteger = BigInteger.valueOf(Integer.decode(intValue));
        return bigInteger.toString(16);
    }

    public static String encodeUsingBigIntegerToString(byte[] bytes) {
        BigInteger bigInteger = new BigInteger(1, bytes);
        return bigInteger.toString(16);
    }

    public static byte[] decodeUsingBigInteger(String hexString) {
        byte[] byteArray = new BigInteger(hexString, 16).toByteArray();
        if (byteArray[0] == 0) {
            byte[] output = new byte[byteArray.length - 1];
            System.arraycopy(byteArray, 1, output, 0, output.length);
            return output;
        }
        return byteArray;
    }
}