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package com.sap.it.commons.tools;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class DigestTools {
    private DigestTools() {

    }

    public static final String MD5 = "md5";

    static MessageDigest getDigest(String digest) {
        try {
            return MessageDigest.getInstance(digest);
        } catch (NoSuchAlgorithmException e) {
            throw new IllegalArgumentException("Digest " + digest + " not found", e);
        }
    }

    private static final char[] HEX_DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

    static char[] encodeHexAsChars(byte[] data) {
        int length = data.length;
        char[] res = new char[length * 2];
        int j = 0;

        for (int i = 0; i < length; ++i) {
            res[j++] = HEX_DIGITS[(0xF0 & data[i]) >>> 4];
            res[j++] = HEX_DIGITS[(0x0F & data[i])];
        }
        return res;
    }

    static String encodeHexString(byte[] data) {
        return String.valueOf(encodeHexAsChars(data));
    }

    public static String compute(String algorithm, String data) {
        MessageDigest dig = getDigest(algorithm);
        int length = data.length();
        for (int i = 0; i < length; ++i) {
            char c = data.charAt(i);
            dig.update((byte) (c >> 8));
            dig.update((byte) (c));
        }
        return encodeHexString(dig.digest());
    }

    public static String computeMD5(String data) {
        return compute(MD5, data);
    }

}