/**
 * 
 */
package hashing;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.math.BigInteger;
import java.nio.charset.StandardCharsets;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;

import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;

/**
 * @author pratikdas
 *
 */
public class HashCreator {

	public String createMD5Hash(final String input) throws NoSuchAlgorithmException{
        String hashtext = null;
		MessageDigest md = MessageDigest.getInstance("MD5");
        // Compute message digest of the input
        byte[] messageDigest = md.digest(input.getBytes());

        hashtext = convertToHex(messageDigest);
		
 		return hashtext;
	}
	
    public String createSHAHash(final String input) throws NoSuchAlgorithmException { 
       String hashtext = null;
       MessageDigest md = MessageDigest.getInstance("SHA-256");
	   byte[] messageDigest =  md.digest(input.getBytes(StandardCharsets.UTF_8)); 
	   System.out.println(messageDigest.length);
	   
	   hashtext = convertToHex(messageDigest);
       return hashtext;
    }

	private String convertToHex(final byte[] messageDigest) {
		BigInteger bigint = new BigInteger(1, messageDigest);
        String hexText = bigint.toString(16);
        while (hexText.length() < 32) {
        	hexText = "0".concat(hexText);
        }
		return hexText;
	}
	
	public String createPasswordHashWithSalt(final String textToHash) {
		try {
			byte[] salt = createSalt();
			return createSaltedHash(textToHash, salt);
		}catch(Exception e) {
			e.printStackTrace();
		}
		return null;
	}
	
    private String createSaltedHash(final String textToHash, final byte[] salt) throws NoSuchAlgorithmException{
            String saltedHash = null;
            // Create MessageDigest instance for MD5
            MessageDigest md = MessageDigest.getInstance("MD5");
            //Add salted bytes to digest
            md.update(salt);
            //Get the hash's bytes 
            byte[] bytes = md.digest(textToHash.getBytes());
            //Convert it to hexadecimal format to
            //get complete salted hash in hex format
            saltedHash = convertToHex(bytes);
            return saltedHash;
    }
    
    
    public String generateStrongPasswordHash(final String password) 
    	    throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchProviderException
    	{
    	    int iterations = 1000;
    	    byte[] salt = createSalt();

    	    byte[] hash = createPBEHash(password,iterations, salt, 64); // skf.generateSecret(spec).getEncoded();
    	    
    	    return iterations + ":" + convertToHex(salt) + ":" + convertToHex(hash);
    }
    //Create salt
    private byte[] createSalt() throws NoSuchAlgorithmException, NoSuchProviderException{
        //Always use a SecureRandom generator for random salt
        SecureRandom sr = SecureRandom.getInstance("SHA1PRNG", "SUN");
        //Create array for salt
        byte[] salt = new byte[16];
        //Get a random salt
        sr.nextBytes(salt);
        //return salt
        return salt;
    }
 
    private boolean validatePassword(final String originalPassword, final String storedPasswordHash) 
    	    throws NoSuchAlgorithmException, InvalidKeySpecException
    	{
    	    // Split the string by :
    	    String[] parts = storedPasswordHash.split(":");

    	    // Extract iterations, salt, and hash 
    	    // from the stored password hash
    	    int iterations = Integer.valueOf(parts[0]); 
    	    byte[] salt = convertToBytes(parts[1]);
    	    byte[] hash = convertToBytes(parts[2]);

    	    byte[] originalPasswordHash = createPBEHash(originalPassword, iterations, salt, hash.length);

    	    int diff = hash.length ^ originalPasswordHash.length;
    	    for(int i = 0; i < hash.length && i < originalPasswordHash.length; i++){
    	        diff |= hash[i] ^ originalPasswordHash[i];
    	    }
    	    return diff == 0;
    }

	private byte[] createPBEHash(final String password, final int iterations, final byte[] salt, final int keyLength)
			throws NoSuchAlgorithmException, InvalidKeySpecException {
		PBEKeySpec spec = new PBEKeySpec(password.toCharArray(), 
		    salt, iterations, keyLength * 8);
		SecretKeyFactory skf = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
		return skf.generateSecret(spec).getEncoded();
	}
    
    private byte[] convertToBytes(final String hex) throws NoSuchAlgorithmException
    {
        byte[] bytes = new byte[hex.length() / 2];
        
        for(int i = 0; i < bytes.length ;i++){
            bytes[i] = Integer.valueOf(hex.substring(2 * i, 2 * i + 2), 16).byteValue();
        }
        return bytes;
    }
    
    public String createChecksum(final String filePath) throws FileNotFoundException, IOException, NoSuchAlgorithmException {
    	MessageDigest md = MessageDigest.getInstance("SHA-256");
        try (
        		
        	DigestInputStream dis = new DigestInputStream(
        			new FileInputStream(filePath), md)) {
            while (dis.read() != -1) ; 
            md = dis.getMessageDigest();
        }
        
        String checksum = convertToHex(md.digest());
        return checksum;
    }
	
	public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchProviderException, FileNotFoundException, IOException {
		    HashCreator hashCreator = new HashCreator();
		
		    String hash = hashCreator.createMD5Hash("password123");
			System.out.println(hash + " "+hash.length());
			
			hash = hashCreator.createSHAHash("password123");
			System.out.println(hash+ " "+hash.length());
					
			String saltedHash = hashCreator.createPasswordHashWithSalt("password123");
			System.out.println(saltedHash);
			
			String strongPwdHash = hashCreator.generateStrongPasswordHash("password123");
			System.out.println(strongPwdHash);
			
			boolean matchResult = hashCreator.validatePassword("password123", strongPwdHash);
			System.out.println("matchResult "+matchResult);
			
			String checksum = hashCreator.createChecksum("/Users/pratikdas/Downloads/heart.csv");
			System.out.println("checksum "+checksum);
	}

}