package me.rafaskb.hasher;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.security.DigestException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashSet;
import java.util.Set;

public class Main {

    public static void main(String[] args) {
        try {
            new Main().crack();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
    }

    private void crack() throws NoSuchAlgorithmException {
        String charsTextField = "1234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM";
        String hashAlgorithm = "MD5"; // MD5 or SHA1
        String hashString = "5d41402abc4b2a76b9719d911017c592"; // hello

        // remove duplicates from chars
        String chars = null;
        {
            String tmp = charsTextField;
            Set<Character> characters = new HashSet<Character>();
            StringBuilder s = new StringBuilder();
            for(int i = 0; i < tmp.length(); ++i) {
                char c = tmp.charAt(i);
                if(characters.add(c)) {
                    s.append(c);
                }
            }
            chars = s.toString();
        }

        CharBuffer charBuffer = CharBuffer.allocate(hashString.length());
        ByteBuffer byteBuffer = ByteBuffer.allocate(hashString.length());
        StringBuilder sb = new StringBuilder();

        CharSequence hash;

        charBuffer.append(chars.charAt(0));

        MessageDigest messageDigest = MessageDigest.getInstance(hashAlgorithm);

        while(true) {
            // check string
            byteBuffer.clear();
            byteBuffer.put(toBytes(charBuffer.array(), byteBuffer.array()));
            hash = hashString(messageDigest, byteBuffer.array(), 0, byteBuffer.limit(), sb);

            if(hashString.equals(hash)) {
                final String solution = new String(byteBuffer.array(), Charset.forName("UTF-8"));
                System.out.println("Success!");
                System.out.println("The answer is \"" + solution + "\"!");
                break;
            }

            // inc string
            for(int i = 0; i < charBuffer.limit(); i++) {
                if(charBuffer.get(charBuffer.limit() - 1 - i) != chars.charAt(charBuffer.limit() - 1)) {
                    charBuffer.put(charBuffer.limit() - 1 - i,
                        chars.charAt(chars.indexOf(charBuffer.get(charBuffer.limit() - 1 - i)) + 1));

                    for(int j = charBuffer.limit() - i; j < charBuffer.limit(); j++) {
                        charBuffer.put(j, chars.charAt(0));
                    }
                    break;
                }

                if(i == charBuffer.limit() - 1) {
                    for(int j = 0; j < charBuffer.limit(); j++) {
                        charBuffer.put(j, chars.charAt(0));
                    }
                    charBuffer.append(chars.charAt(0));
                    break;
                }
            }
        }
    }

    public CharSequence hashString(MessageDigest m, byte[] buf, int offset, int len, StringBuilder sb) {
        try {
            sb.delete(0, sb.length());
            sb.setLength(0);
            m.reset();

            m.digest(buf, offset, len);

            for(int i = 0; i < buf.length; ++i)
                sb.append(Integer.toHexString((buf[i] & 0xFF) | 0x100).substring(1, 3));

            return sb;
        } catch (DigestException e) {
            e.printStackTrace();
        }
        return null;
    }

    private byte[] toBytes(char[] data, byte[] result) {
        for(int i = 0; i < result.length; i++) {
            result[i] = i < data.length ? (byte) data[i] : 0;
        }
        return result;
    }

}