package top.keepempty;

import org.junit.Test;


/**
 * Example local unit test, which will execute on the development machine (host).
 *
 * @see <a href="http://d.android.com/tools/testing">Testing documentation</a>
 */
public class ExampleUnitTest {
    @Test
    public  void  addition_isCorrect() {
        System.out.println(decodeHexString("A"));
        System.out.println(decToHex(13));
    }

    public static String decToHex(int dec
    ){
        String hex = Integer.toHexString(dec);
        if (hex.length() == 1) {
            hex = '0' + hex;
        }
        return hex.toLowerCase();
    }


    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 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;
    }

}