package com.caimei.utils;

import java.security.MessageDigest;

public class HashUtil {

    private static final java.security.SecureRandom random = new java.security.SecureRandom();
    private static final char[] HEX_DIGITS = "0123456789abcdef".toCharArray();
    private static final char[] CHAR_ARRAY = "_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();

    public static String md5(String srcStr) {
        return hash("MD5", srcStr);
    }

    public static String sha1(String srcStr) {
        return hash("SHA-1", srcStr);
    }

    public static String sha256(String srcStr) {
        return hash("SHA-256", srcStr);
    }

    public static String sha384(String srcStr) {
        return hash("SHA-384", srcStr);
    }

    public static String sha512(String srcStr) {
        return hash("SHA-512", srcStr);
    }

    public static String hash(String algorithm, String srcStr) {
        try {
            MessageDigest md = MessageDigest.getInstance(algorithm);
            byte[] bytes = md.digest(srcStr.getBytes("utf-8"));
            return toHex(bytes);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static String toHex(byte[] bytes) {
        StringBuilder ret = new StringBuilder(bytes.length * 2);
        for (int i = 0; i < bytes.length; i++) {
            ret.append(HEX_DIGITS[(bytes[i] >> 4) & 0x0f]);
            ret.append(HEX_DIGITS[bytes[i] & 0x0f]);
        }
        return ret.toString();
    }

    /**
     * md5 128bit 16bytes
     * sha1 160bit 20bytes
     * sha256 256bit 32bytes
     * sha384 384bit 48bytes
     * sha512 512bit 64bytes
     */
    public static String generateSalt(int saltLength) {
        StringBuilder salt = new StringBuilder(saltLength);
        for (int i = 0; i < saltLength; i++) {
            salt.append(CHAR_ARRAY[random.nextInt(CHAR_ARRAY.length)]);
        }
        return salt.toString();
    }

    public static String generateSaltForSha256() {
        return generateSalt(32);
    }

    public static String generateSaltForSha512() {
        return generateSalt(64);
    }

    public static boolean slowEquals(byte[] a, byte[] b) {
        if (a == null || b == null) {
            return false;
        }

        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;
    }
}