package com.nanjing.water.common.util;


import org.springframework.util.Base64Utils;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.util.Random;

public class SM4Util {
    /**
     * 算法名字
     */
    private static final String NAME = "SM4";
    /**
     * 加密模式以及短快填充方式
     */
    private static final String ALGORITHM = "SM4/CBC/PKCS5Padding";
    /**
     * 加密使用的初始向量
     */
    private static final String IV = "0000000000000000";
    /**
     * 密钥长度(128-32位16进制；256-64位16进制)
     */
    private static final int KEY_SIZE = 16;

    private static final String ALL_STR = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

    public static String generateKey() {
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < KEY_SIZE; i++) {
            int number = random.nextInt(ALL_STR.length());
            sb.append(ALL_STR.charAt(number));
        }
        return sb.toString();
    }

    /**
     * 使用指定的加密算法和密钥对给定的字节数组进行加密
     *
     * @param content 待加密的原始字符串
     * @param key     密钥(注意必须是128bits，即16个字节)
     * @return 加密后的字符串
     * @throws Exception 如果加密时发生错误，则抛出异常
     */
    public static String encode(String content, String key) throws Exception {
        try {
            byte[] inputByte = content.getBytes(StandardCharsets.UTF_8);
            byte[] keyBuffer = key.getBytes(StandardCharsets.UTF_8);

            // 获取加密实例
            Cipher c = Cipher.getInstance(ALGORITHM);
            // 根据密钥的字节数组创建 SecretKeySpec
            SecretKeySpec secretKeySpec = new SecretKeySpec(keyBuffer, NAME);
            // 创建 IvParameterSpec 对象，使用默认向量和字符集
            IvParameterSpec ivParameterSpec = new IvParameterSpec(IV.getBytes(StandardCharsets.UTF_8));
            // 初始化加密实例
            c.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivParameterSpec);
            // 返回加密后的字节数组
            byte[] buffer = c.doFinal(inputByte);
            return Base64Utils.encodeToString(buffer);
        } catch (Exception e) {
            throw new Exception("加密失败: " + e, e);
        }
    }

    /**
     * 解密
     *
     * @param content 待解密字符串
     * @param key     密钥(注意必须是128bits，即16个字节)
     * @return 解密后的原始字符串
     * @throws Exception 如果解密时发生错误，则抛出异常
     */
    public static String decode(String content, String key) throws Exception {
        try {
            byte[] inputBytes = Base64Utils.decode(content.getBytes(StandardCharsets.UTF_8));
            byte[] keyBuffer = key.getBytes(StandardCharsets.UTF_8);
            Cipher cipher = Cipher.getInstance(ALGORITHM);
            SecretKeySpec secretKeySpec = new SecretKeySpec(keyBuffer, NAME);
            IvParameterSpec ivParameterSpec = new IvParameterSpec(IV.getBytes(StandardCharsets.UTF_8));
            cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);
            byte[] buffer = cipher.doFinal(inputBytes);
            return new String(buffer, StandardCharsets.UTF_8);
        } catch (Exception e) {
            throw new Exception("解密失败: " + e, e);
        }
    }
}