package com.wind.encrypt;

import com.wind.common.StringUtil;

import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;

/**
 * @Title: CryptoUtil
 * @Package com.wind.encrypt
 * @Description: PBKDF2
 * @author wind
 * @date 2018/10/11 10:12
 * @version V1.0
 */
public class CryptoUtil {

    public static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1";

    /**
     * The following constants may be changed without breaking existing hashes.
     */
    public static final int SALT_BYTE_SIZE = 24;
    public static final int HASH_BYTE_SIZE = 24;
    public static final int PBKDF2_ITERATIONS = 1000;

    public static final int ITERATION_INDEX = 0;
    public static final int SALT_INDEX = 1;
    public static final int PBKDF2_INDEX = 2;

    public static final int PWD_SALT_LEN = 2;

    /**
     * Returns a salted PBKDF2 hash of the password.
     *
     * @param password
     *            the password to hash
     * @return a salted PBKDF2 hash of the password 数组第一个元素是密码,第二个元素是hash次数和随机盐
     */
    public static String[] createHash(String password) throws NoSuchAlgorithmException, InvalidKeySpecException {
        if (!StringUtil.isNotBlank(password)) {
            return new String[PWD_SALT_LEN];
        }
        return createHash(password.toCharArray());
    }

    /**
     * Returns a salted PBKDF2 hash of the password.
     *
     * @param password
     *            the password to hash
     * @return a salted PBKDF2 hash of the password 数组第一个元素是密码,第二个元素是hash次数和随机盐
     */
    private static String[] createHash(char[] password) throws NoSuchAlgorithmException, InvalidKeySpecException {
        // Generate a random salt
        SecureRandom random = new SecureRandom();
        byte[] salt = new byte[SALT_BYTE_SIZE];
        random.nextBytes(salt);

        // Hash the password
        byte[] hash = pbkdf2(password, salt, PBKDF2_ITERATIONS, HASH_BYTE_SIZE);
        // format iterations:salt:hash
        return new String[] { toHex(hash), PBKDF2_ITERATIONS + ":" + toHex(salt)};
    }

    /**
     * Validates a password using a hash.
     *
     * @param password
     *            the password to check
     * @param salt
     *            the hash of the valid password
     * @return true if the password is correct, false if not
     */
    public static boolean validatePassword(String password, String hashPwd, String salt)
            throws NoSuchAlgorithmException, InvalidKeySpecException {
        if (!StringUtil.isNotBlank(password) || !StringUtil.isNotBlank(hashPwd)
                || !StringUtil.isNotBlank(salt)) {
            return false;
        }
        return validatePassword(password.toCharArray(), hashPwd, salt);
    }

    /**
     * Validates a password using a hash.
     *
     * @param password
     *            the password to check
     * @param salt
     *            the hash of the valid password
     * @return true if the password is correct, false if not
     */
    private static boolean validatePassword(char[] password, String hashPwd, String salt)
            throws NoSuchAlgorithmException, InvalidKeySpecException {
        // Decode the hash into its parameters
        String[] params = salt.split(":");
        if (params.length != PWD_SALT_LEN) {
            return false;
        }
        int iterations = Integer.parseInt(params[ITERATION_INDEX]);
        byte[] saltByte = fromHex(params[SALT_INDEX]);
        // fromHex(params[PBKDF2_INDEX]);
        byte[] hash = fromHex(hashPwd);
        // Compute the hash of the provided password, using the same salt,
        // iteration count, and hash length
        byte[] testHash = pbkdf2(password, saltByte, iterations, hash.length);
        // Compare the hashes in constant time. The password is correct if
        // both hashes match.
        return slowEquals(hash, testHash);
    }

    /**
     * Validates a password using a hash.
     *
     * @param password
     *            the password to check
     * @param salt
     *            the hash of the valid password
     * @return true if the password is correct, false if not
     */
    private static boolean validatePassword(char[] password, String salt)
            throws NoSuchAlgorithmException, InvalidKeySpecException {
        // Decode the hash into its parameters
        String[] params = salt.split(":");
        int iterations = Integer.parseInt(params[ITERATION_INDEX]);
        byte[] saltByte = fromHex(params[SALT_INDEX]);
        byte[] hash = fromHex(params[PBKDF2_INDEX]);
        // Compute the hash of the provided password, using the same salt,
        // iteration count, and hash length
        byte[] testHash = pbkdf2(password, saltByte, iterations, hash.length);
        // Compare the hashes in constant time. The password is correct if
        // both hashes match.
        return slowEquals(hash, testHash);
    }

    /**
     * Compares two byte arrays in length-constant time. This comparison method
     * is used so that password hashes cannot be extracted from an on-line
     * system using a timing attack and then attacked off-line.
     *
     * @param a
     *            the first byte array
     * @param b
     *            the second byte array
     * @return true if both byte arrays are the same, false if not
     */
    private static boolean slowEquals(byte[] a, byte[] b) {
        int diff = a.length ^ b.length;
        for (int i = 0; i < a.length && i < b.length; i++) {
            diff |= a[i] ^ b[i];
        }
        return diff == 0;
    }

    /**
     * Computes the PBKDF2 hash of a password.
     *
     * @param password
     *            the password to hash.
     * @param salt
     *            the salt
     * @param iterations
     *            the iteration count (slowness factor)
     * @param bytes
     *            the length of the hash to compute in bytes
     * @return the PBDKF2 hash of the password
     */
    private static byte[] pbkdf2(char[] password, byte[] salt, int iterations, int bytes)
            throws NoSuchAlgorithmException, InvalidKeySpecException {
        PBEKeySpec spec = new PBEKeySpec(password, salt, iterations, bytes * 8);
        SecretKeyFactory skf = SecretKeyFactory.getInstance(PBKDF2_ALGORITHM);
        return skf.generateSecret(spec).getEncoded();
    }

    /**
     * Converts a string of hexadecimal characters into a byte array.
     *
     * @param hex
     *            the hex string
     * @return the hex string decoded into a byte array
     */
    private static byte[] fromHex(String hex) {
        byte[] binary = new byte[hex.length() / 2];
        for (int i = 0; i < binary.length; i++) {
            binary[i] = (byte) Integer.parseInt(hex.substring(2 * i, 2 * i + 2), 16);
        }
        return binary;
    }

    /**
     * Converts a byte array into a hexadecimal string.
     *
     * @param array
     *            the byte array to convert
     * @return a length*2 character string encoding the byte array
     */
    private static String toHex(byte[] array) {
        BigInteger bi = new BigInteger(1, array);
        String hex = bi.toString(16);
        int paddingLength = (array.length * 2) - hex.length();
        if (paddingLength > 0) {
            return String.format("%0" + paddingLength + "d", 0) + hex;
        } else {
            return hex;
        }
    }
}
