package com.alterdekim.javabot.util;

import lombok.extern.slf4j.Slf4j;

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;

@Slf4j
public class HashUtils {
    public static String md5(String s) {
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            byte[] theMD5digest = md.digest(s.getBytes(StandardCharsets.UTF_8));
            return bytesToHex(theMD5digest);
        } catch ( Exception e ) {
            log.error(e.getMessage());
        }
        return null;
    }

    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;
    }

    private 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;
    }

    private static final byte[] HEX_ARRAY = "0123456789ABCDEF".getBytes(StandardCharsets.US_ASCII);
    public static String bytesToHex(byte[] bytes) {
        byte[] hexChars = new byte[bytes.length * 2];
        for (int j = 0; j < bytes.length; j++) {
            int v = bytes[j] & 0xFF;
            hexChars[j * 2] = HEX_ARRAY[v >>> 4];
            hexChars[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
        }
        return new String(hexChars, StandardCharsets.UTF_8);
    }
}